The helicity density matrix elements, rho(0,0), of rho(770)+/- and omega(782) mesons produced in Z0 decays have been measured using the OPAL detector at LEP. Over the measured meson energy range, the values are compatible with 1/3, corresponding to a statistical mix of helicity -1, 0 and +1 states. For the highest accessible scaled energy range 0.3 < x_E < 0.6, the measured rho(0,0) values are 0.373+/-0.052 and 0.142+/-0.114 for the rho and omega mesons respectively. These results are compared to measurements of other vector mesons.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP/99-082, submitted to Eur. Phys. J. C = http://opal.web.cern.ch/Opal/pubs/paper/html/pr280.html
Notes:Also Parallel session 3, Jets, Plenary Session 11, Jets.
Bose-Einstein correlations in pairs of charged kaons produced in a sample of 3.9 million hadronic Z0 decays have been measured with the OPAL experiment at LEP. Charged kaons were identified in the central tracking detector using their specific energy loss in the drift chamber gas. The correlation function was studied in two-jet events using a double ratio, formed by the number of like-sign pairs normalised by a reference sample in the data, divided by the same ratio in a Monte Carlo simulation. The enhancement at small values of the four-momentum difference of the pair was parametrised using a Gaussian function. Corrections for final-state interactions are discussed.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP/99-163, submitted to Eur. Phys. J. C = http://opal.web.cern.ch/Opal/pubs/paper/html/pr295.html
Notes:
Bose-Einstein correlations in pairs of identical charged pions, produced in a sample of 4.3 million Z0 hadronic decays, are studied as a function of the three components of the momentum difference transverse and longitudinal to the thrust direction of the event. A significant difference between the transverse and longitudinal dimensions is observed, indicating that the emitting source, as observed in the Longitudinally CoMoving System, has an elongated shape. Measurements of the effective transverse and longitudinal sizes of the source are presented and discussed in the context of a recent model of Bose-Einstein correlations based on string fragmentation.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP-2000-0004, submitted to Eur. Phys. J. C = http://opal.web.cern.ch/Opal/pubs/paper/html/pr302.html
Notes:
The inclusive production of charged D* mesons in photon-photon collisions has been measured using the OPAL detector at LEP at e+e- centre-of-mass energies of 183 and 189 GeV. Direct and single-resolved events are studied separately. Differential cross-sections as functions of the D* transverse momentum and pseudorapidity are presented in the kinematic region 2 GeV < pt_D* < 12 GeV and |eta_D*| < 1.5. They are compared to next-to-leading order (NLO) perturbative QCD calculations. The total cross-section for the process e+e- --> e+e- c cbar where the charm quarks are produced in the collision of two quasi-real photons is measured to be 842 +- 97(stat) +- 75(syst) +- 196 (extrapol.) pb
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP/99-157, Submitted to Eur. Phys. J. C =http://opal.web.cern.ch/Opal/pubs/paper/html/pr294.html
Notes:Also Parallel session 3, Jets; Plenary session 11, Jets.
The inclusive production of charged D* mesons in deep inelastic electron-photon scattering has been used to extract the charm structure function of the photon in the kinematic range 0.0014 < x < 0.87 and 5 GeV^2 <Q^2 < 100 GeV^2. The data were taken with the OPAL detector at LEP at e+e- centre-of-mass energies of 183 and 189 GeV. The result is compared to an NLO perturbative QCD calculation.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP/99-157, Submitted to Eur. Phys. J. C =http://opal.web.cern.ch/Opal/pubs/paper/html/pr294.html
Notes:Also Parallel session 3, Jets; Plenary session 11, Jets.
The total hadronic cross-section for the interaction of real photons, is measured for Photon-Photon centre-of-mass energies of 10 < W < 110 GeV. The Photon-Photon cross-section is extracted from a measurement of the process e+e- --> e+e- Gamma^* Gamma^* --> e+e- + Hadrons using a luminosity function for the photon flux and form factors for extrapolating to real photons (Q^2=0). The data were taken with the OPAL detector at LEP at e+e- centre-of-mass energies of 161 to 183 GeV. The cross-section is compared with Regge factorisation and with the energy dependence observed in Photon-Proton and Proton-Proton interactions. The data are also compared to models which predict a faster rise of the total hadronic cross-section due to additional hard Photon-Photon interactions not present in hadronic collisions.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP/99-076, Submitted to Eur. Phys. J. C =http://opal.web.cern.ch/Opal/pubs/paper/html/pr278.html
Notes:
The structure of both quasi-real and highly virtual photons is investigated using the reaction e+e- --> e+e- mu+mu-, proceeding via the exchange of two photons. The results are based on the complete OPAL dataset taken at e+e- centre-of-mass energies close to the mass of the Z boson. The QED structure function and the differential cross-section for quasi-real photons are obtained as functions of the fractional momentum x from the muon momentum which is carried by the struck muon in the quasi-real photon for values of Q^2 ranging from 1.5 to 400 GeV^2. The differential cross-section for highly virtual photons is measured for 1.5 < Q^2 < 30 GeV^2 and 1.5 < P^2 < 20 GeV^2, where Q^2 and P^2 are the negative values of the four-momentum squared of the two photons such that Q^2 > P^2. Based on azimuthal correlations the QED structure functions for quasi-real photons are determined for an average Q^2 of 5.4 GeV^2.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP/99-010, Eur. Phys. J. C11 (1999) 409-425 =http://opal.web.cern.ch/Opal/pubs/paper/html/pr271.html
Notes:
A multidimensional study of local multiplicity fluctuations and multiparticle correlations of hadrons produced in Z0 decays is performed. The fluctuations and correlations are analysed using normalized scaled factorial moments and cumulants up to fifth order. The moments have intermittent-like behaviour, which is found to be more pronounced with increasing dimension. The analysis of the cumulants shows the existence of genuine multiparticle correlations. The decomposition of the factorial moments shows that the dynamical fluctuations have important contributions from genuine many-particle correlations. The results are consistent with QCD jet formation dynamics, although additional contributions from other mechanisms cannot be excluded.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: CERN-EP/99-009, Eur. Phys. J. C11 (1999) 239-250 =http://opal.web.cern.ch/Opal/pubs/paper/html/pr270.html
Notes:
Gluon distribution for a large nuclues can be computed from first principle using classical chromodynamics. We incorporate confinement into this idea of McLerran and Venugopalan, and allow the longitudinal structure of the nucleus also to be resolved. The former eliminates infrared divergences in the original model, and allows computation into regions of relatively small transverse momenta. The latter makes it possible for distributions at larger longitudinal momentum fractions to be computed. Both model-independent features and results from specific nucleon models will be presented.
Authors:H.C.S. Lam and Gregory Mahlon
Proposed speaker: Harry C.S. Lam
Contact person:Harry C.S. Lam
(McGill University),
Lam@physics.mcgill.ca
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-15 High Energy Heavy Ion Collisions
Supporting papers: 1. C.S. Lam and Gregory Mahlon, Color neutrality and the gluon distribution in a very large nucleus, Phys. Rev. D61, 014005 (2000) 2. C.S. Lam and Gregory Mahlon, in preparation
Notes:
We extend our previous treatment of $\gamma^{*}$p cross section based on Gribov's hypothesis to the case of photon-photon scattering. With the aid of two parameters, determined from experimental data, we separate the interactions into two categories corresponding to short ("soft") and long ("hard") distance processes. The photon-photon cross section, thus, receives contributions from three sectors, soft-soft, hard-hard and hard-soft. The additive quark model is used to describe the soft-soft sector, pQCD the hard-hard sector, while the hard-soft sector is determined by relating it to the $\gamma^{*}$p system. We calculate and display the behaviour of the total photon-photon cross section and it's various components and polarizations for different values of energy and virtuality of the two photons, and discuss the significance of our results.
Authors: E. Gotsman, E. Levin, U. Maor and E. Naftali. (Tel-Aviv U.)
Proposed speaker: Uri Maor
Contact person:Uri Maor
(Tel Aviv University),
maor@post.tau.ac.il
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: hep-ph/0001080 (Accepted to Eur. Phys. J C)
Notes:
The soft pion at high energy in the lepton-hadron reactions is studied by using the sum rules for the sea quarks. It is shown that it plays an important role in high energy reactions such as the charge asymmetry in the central region, Gottfried sum defect and the contribution to the strange sea quark distribution in the small x region. These facts suggest us that,in many high energy reactions, the quantity related to the remnant of the spontaneous chiral symmetry breakings remains, which without this is difficult to undestand.
Authors:Susumu Koretune
Proposed speaker: Susumu Koretune
Contact person:Susumu Koretune
(Shimane Medical Univ.),
koretune@shimane-med.ac.jp
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: hep-ph/9912507(Prog.Theor.Phys.V.103,127(2000)) hep-ph/0004149
Notes:
The cross section for the process e+e- --> e+e- Gamma^* Gamma^* --> e+e- X, where X denotes the hadronic final state, has been measured using the OPAL detector. Both scattered electrons have been tagged in the silicon-tungsten luminometers. The results are compared to Monte Carlo models and BFKL calculations.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: To be submitted to the conference and listed on http://opal.web.cern.ch/Opal/pubs/publications.html
Notes:
Deep inelastic electron-photon scattering has been studied using data taken by the OPAL detector at centre-of-mass energies of 91 to 189 GeV, exploring the photon structure function in Q^2 ranges of 1.5 to 30 GeV^2 (LEP1), and 6 to 30 GeV^2 (LEP2), probing the lowest x attainable. The latest Monte Carlos and new methods, such as multi-variable unfolding, have been explored to reduce model dependent systematic errors on the structure function.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: To be submitted to the conference and listed on http://opal.web.cern.ch/Opal/pubs/publications.html
Notes:
We study di-jet production in untagged two photon events using LEP 2 data collected at [root s] = 183 GeV. The jets are reconstructed with a clustering algorithm, KTCLUS. The inclusive di-jet cross section is measured as a function of Pt and |pseudorapidity_jet| and compared to NLO perterbative QCD calculations.
Authors:ALEPH collaboration
Proposed speaker:
Contact person:Fabrizio Palla
(CERN),
Fabrizio.Palla@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:5/18/00 TY-Palla notified us that the sessoins should be PA-02/PL-12 instead of PA-03/PL-11.
We study jet production in tagged two photon events using LEP 2 data collected at a center of mass energy of 183 GeV. The jets are reconstructed with a cone based algorithm. The results are compared to NLO order QCD calculations from the JetViP program.
Authors:ALEPH collaboration
Proposed speaker:
Contact person:Fabrizio Palla
(CERN),
Fabrizio.Palla@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:5/18/00 TY-Palla notified us that the sessoins should be PA-02/PL-12 instead of PA-03/PL-11.
The inclusive production of D*+ mesons has been measured using the ALEPH detector at LEP II for center-of-mass energies in the range 183-189 GeV. The D*+ meson is reconstructed in the decay D*+ -> D0 pi+. The D0 in turn is identified in the decay modes K- pi+, K- pi+ pi0, K- pi+ pi- pi+. The relative contributions of the dominant direct and single resolved processes have been determined. Differential cross sections in the transverse momentum and in the pseudorapidity of the D*+ are provided as well as the total cross section. The results are compared to theoretical predictions.
Authors:ALEPH collaboration
Proposed speaker:
Contact person:Fabrizio Palla
(CERN),
Fabrizio.Palla@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:5/18/00 TY-Palla notified us that the sessoins should be PA-02/PL-12 instead of PA-03/PL-11.
The cross section for inclusive charm production in two-photon-interactions is measured at a centre-of-mass energy of 183 GeV. The data are taken with the ALEPH - experiment at LEP. Charmed hadrons are identified by muons from semi-leptonic decays. The measured cross section is found to be consistent with results from other experiments and theoretical predictions.
Authors:ALEPH collaboration
Proposed speaker:
Contact person:Fabrizio Palla
(CERN),
Fabrizio.Palla@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:5/18/00 TY-Palla notified us that the sessoins should be PA-02/PL-12 instead of PA-03/PL-11.
Using the DZero detector, we study events produced in proton- antiproton collisions that contain large forward regions with very little energy deposition (`rapidity gaps') and concurrent jet production, at center-of-mass energies 630 and 1800 GeV. In addition, we measure properties for similar topologies, but with W or Z bosons produced instead of accompanying jets. The fractions of hard scattering events that have rapidity gaps are compared with predictions from Monte Carlo models. The DZero calorimeter is also used to extract the fractional momentum loss of the scattered protons for hard-diffractive candidate events.
Authors:The DZero Collaboration
Proposed speaker:
Contact person:Bernard G. Pope
(Michigan State University),
pope@pa.msu.edu
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) /
Supporting papers:
Notes:Speaker to be decided by the DZero Collaboration
The hadronic tensor $W_{\mu\nu}$ of deep inelastic scattering is formulated in the path-integral formalism. It is shown that there are two sources for the sea -- one in the connected insertion and the other in the disconnected insertion. We explore the phenomenological consequences of this classification in terms of the small x behavior, Gottfried sum rule violation, and the flavor dependence. In particular, we point out that in the nucleon $\bar{u}$ and $\bar{d}$ partons have both the connected and disconnected sea contributions; whereas, $\bar{s}$ parton has only the disconnected sea contribution. This difference between $\bar{u} + \bar{d}$ and $\bar{s}$ in their small x behaviors has not been taken into account in the fitting of parton distribution functions to experiments.
Authors:Keh-Fei Liu
Proposed speaker: Keh-Fei Liu
Contact person:Keh-Fei Liu
(University of Kentucky),
liu@pa.uky.edu
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: hep-ph/9910306
Notes:
The next-to leading order (NLO) results obtained in the BFKL approach are reviewed, problems encountered in the NLO and proposed solutions of them are discussed. The main assumption of the approach is exhibited. The last results obtained for the generalized non-forward BFKL equation with colour octet state in the t-channel and negative signature permit to check that this assumption is consitent with the s-channel unitarity.
Authors:V.S. Fadin
Proposed speaker: V.S. Fadin
Contact person:Victor Sergeevich Fadin
(Institute for Nuclear Physics),
fadin@inp.nsk.su
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) /
Supporting papers:
Notes:
We investigate the energy dependence and differential cross sections of vector meson photoproduction. Our starting point, which is based on previous studies, is that $\rho$ and $\omega$ photoproduction is predominantly soft and well described by a Regge parameterization, while $J/\Psi$ photoproduction is predominantly hard and well reproduced by a pQCD calculation in the LLA with screening corrections (SC). Photoproduction of $\phi$ mesons corresponds to hardness scales for which we anticipate that both the soft and hard components contribute significantly. Indeed, we show that the energy dependence in $\phi$ photoproduction is steeper than the energy dependence anticipated for a soft process. Our phenomenological study suggests that the transition from the soft to the hard kinematical domain is smooth and gradual, similar to the transition observed in DIS studies of $F_2$ in the small x limit. This conclusion is further supported by a calculation in which we show that a coherent sum of a hard pQCD component and a conventional soft Pomeron provides an excellent reproduction of the experimental data. The pQCD analysis depends on extrapolation of $xG(x,Q^2)$ to small $Q^2$ values. We discuss this procedure in some detail, and also present predictions for higher HERA energies. Our model is conceptually different from the two-Pomeron model of Donnachie and Landshoff (DL), which assumes that both soft and hard contributions are described by fixed J poles modulated by $Q^2$ form factors. In our approach, the hard contribution is calculated by pQCD. It depends on the gluon distribution function $xG(x,Q^2)$ which is not factorized and is considerably softer than in the fixed DL pole case. Consequences of our approach for $J/\Psi$ photoproduction and $\partial F_2/\partial lnQ^2$ are presented and discussed.
Authors:E. Ferreira, E. Gotsman, E. Levin, U. Maor, E. Naftali
Proposed speaker: E. Ferreira
Contact person:Erasmo Ferreira
(Universidade Federal do rio de Janeiro),
erasmo@if.ufrj.br
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The extra singularity at t=0, which is characteristic of the long range force, is searched in the region of the small momentum transfer of the hadron-hadron amplitudes. In terms of the partial wave amplitude, such an extra singularity appears at nu=0. Results of the searches for the S-wave amplitude of p-p and the P-wave amplitude of pi-pi, which are done by removing the near-by known singularities, are presented. Possible appearance of the characteristic destructive interference pattern in the angular distribution of the p-p scattering, which arises from the repulsive Coulomb force and the strong Van der Waals force, is pointed out.
Authors:Tetsuo Sawada
Proposed speaker: Tetsuo Sawada
Contact person:Shin Ishida
(Nihon University),
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) /
Supporting papers:
Notes:
The TOTEM experiment is designed to provide a precise measurement of the total proton-proton cross section at the LHC. A luminosity independent method, that requires the simultaneous measurements of elastic scattering at low momentum transfer and of the total inelastic rate, will be used. The aim is an absolute error of about 1mb. The integration of TOTEM with the machine layout is reviewed and the dedicated LHC beam conditions are discussed. The experiment does not need intense beams nor high luminosity. It is therefore suited for running at the beginning of LHC operation, within a limited amount of machine time.
Authors:TOTEM Collaboration
Proposed speaker: Sylvain WEISZ
Contact person:Sylvain M.J. WEISZ
(CERN),
Sylvain.Weisz@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
We present the parton density dynamics in the asymptotic regime for the distinct formalisms for high density QCD. We show the property of partial saturation of the AGL equation, which is not modified by the running coupling constant. In this regime, we show that the McL-V formalism gives the AGL solution. The F2 structure function is calculed considering unitarity corrections and we get a result equivalent as Korchegov approach. We conclude that F2 unitarizes, respecting Froissart boundary, and that partial saturation of the gluon distribution are general results established from three distinct formalisms for high dense systems.
Authors:M. B. Gay Ducati and V. P. Gonçalves
Proposed speaker: M. B. Gay Ducati
Contact person:Stanley J. Brodsky
(SLAC Stanford University),
sjbth@SLAC.Stanford.EDU
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-11 Hard Interaction Processes ( High Q2 : DIS, Jets )
Supporting papers: A.L. Ayala, M.B. Gay Ducati and E.M. Levin, Nucl. Phys. B493(97); Nucl. Phys. B511(98)355 M.B. Gay Ducati, V.P. Gonçalves, Nucl. Phys. B557(99)296 M.B. Gay Ducati, V.P. Gonçalves, hep-ph/0003098 A.L. Ayala, M.B. Gay Ducati and E.M. Levin, Phys. Lett. B388(96)188 A.L. Ayala, M.B. Gay Ducati and V.P. Gonçalves, Phys. Rev. D59(99)054010 A.L. Ayala, M.B. Gay Ducati and E.M. Levin, Eur. Phys. J. C8(1999)115 M.B. Gay Ducati, V.P. Gonçalves, Phys. Rev. C60(99)058201 M.B. Gay Ducati, V.P. Gonçalves, Phys. Lett. B466(99)375
Notes:
Using the CLEO detector at CESR we have analyzed 13 fb^-1 of data to find approximately 300 events from the process gamma,gamma => eta_c => K0s,K,pi. From this we measured the eta_c mass, full decay width and two-photon partial width.
Authors:CLEO
Proposed speaker: CLEO
Contact person:David E Jaffe
(Cornell University),
cleoac@mail.lns.cornell.edu
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The production of b quarks in gamma-gamma collisions has been studied with the L3 detector at LEP. The data sample used corresponds to a total integrated luminosity of 410 pb-1 collected at the centre-of-mass energies from 189 GeV to 202 GeV. Hadronic final states containing beauty particles are identified by detecting electrons or muons from their semi-leptonic decays. The cross sections (e+e- --> e+e- b bar(b) X) are compared to perturbative next-to-leading order QCD calculations. The cross section of beauty production has been measured in gamma-gamma collisions for the first time.
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:in preparation
Di-jet production is studied in collisions of quasi-real and virtual photons at e+e- centre-of-mass energies from 198 to 200 GeV. The jets are reconstructed using a cluster jet finding algorithm. The inclusive two-jet cross-section is measured as a function of the transverse energy and the pseudorapidity of the jets and compared to NLO perturbative QCD calculations and to the prediction of Monte Carlo generators using different LO parametrisations of the parton distributions of the photon.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: To be submitted to the conference and listed on http://opal.web.cern.ch/Opal/pubs/publications.html
Notes:
Inclusive charm production in gamma-gamma collisions has been studied with the L3 detector at the LEP collider. Hadronic final states containing charm particles were identified by detecting electrons or muons from their semi-leptonic decays. Charm particles in the final state were also identified by the reconstruction of charged D* meson decays. The total cross section for the process e+ e- ---> e+ e- c bar(c) X has been measured at several centre-of-mass energies between 189 GeV and 202 GeV. Even including real and virtual gluon emission (NLO QCD) the direct process gamma-gamma --> c bar (c) is insufficient to describe charm production in gamma-gamma collisions. The cross section values and event distributions require resolved processes, sensitive to the gluon density function of the photon. Including this contribution good agreement is found with NLO QCD predictions. The total cross sections ( e+ e-) --> e+ e- c bar(c) X ) and (gamma-gamma ---> c bar(c) X) are also measured as function of the two-photon centre-of-mass energy in the interval W(gamma-gamma) between 5 GeV and 70 GeV. We observe a steeper rise with energy as compared to hadron-hadron cross sections and to (gamma-gamma --> hadrons).
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:in preparation
Inclusive production of D*+- mesons in two-photon collisions was measured by the L3 experiment at LEP. The data were collected at a centre-of-mass energy sqrt(s) = 189 GeV with an integrated luminosity of 176.4 pb-1. Differential cross sections of the process e+e- ---> D*+- X are determined as functions of the transverse momentum and pseudorapidity of the D*+- mesons in the kinematic region of Pt of D* between 1 GeV and 5 GeV and eta of D* smaller than 1.4. The cross section integrated over this phase space domain is measured to be 132+- 22(stat.)+- 26(syst.) pb. The differential cross sections are compared with next-to-leading order perturbative QCD calculations.
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: L3 Collaboration, M. Acciarri et al., Phys. Lett. B 467/1-2 (11 November, 1999) 137-146. CERN-EP/99-106, 27 July 1999. L3 preprint 180. Measurement of Inclusive D*+- Production in Two-Photon Collisions at LEP.
Notes:
A study of double tag events using the L3 detector at LEP has been performed. Data were collected at centre-of-mass energies from 189 GeV to 202 GeV for a total integrated luminosity of 410 pb-1. The cross-section of gamma*-gamma* collisions is measured at average momentum transfer squared < Q2 > = 15 GeV2. The results are in agreement with predictions based on perturbative QCD (PHOJET Monte Carlo model), while the Quark Parton Model alone is insufficient to describe the data. The measurements lie well below the LO BFKL prediction, but agree with the improved NLO BFKL calculations.
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:in preparation
The structure functions of real and virtual photons are derived from cross section measurements of the reaction e+e- ---> e+e- + (hadrons) at LEP. The reaction is studied at sqrt(s) approximatly equal 91 GeV with the L3 detector. One of the final state electrons is detected at a large angle relative to the beam direction, leading to Q2 values between 40 GeV2 and 500 GeV2. The other final state electron is either undetected or it is detected at a four-momentum transfer squared P2 between 1 GeV2 and 8 GeV2. These measurements are compared with predictions of the Quark Parton Model and other QCD based models.
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: L3 Collab., M. Acciarri et al., Physics letters B Submitted CERN-EP-2000-044; 09 February 2000. L3 preprint 204. Measurement of the Photon Structure Function at High Q2 at LEP.
Notes:
The inclusive production of K0_s mesons in the reaction e+e- ----> e+e- hadrons is studied with the L3 detector at LEP. Data were collected at centre-of-mass energies from 189 GeV to 202 GeV for a total integrated luminosity of 410 pb-1. The differential cross sections as a function of the transverse momentum and of the pseudorapidity of the K0_s are measured. The results are compared to the predictions of PHOJET and PYTHIA Monte Carlo models and to perturbative next-to-leading order QCD calculations.
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:in preparation
The virtual photon structure function is extracted from a measurement of the cross section for the process e+e- -> e+e- gamma*gamma* -> e+e-X, where X denotes the hadronic final state, using the OPAL detector based on data from the 1998 LEP run. The scattered electrons have been tagged in the OPAL luminometers. The upgrade of four calorimeter modules in the very forward region at OPAL (z=7.8m) allows to study the virtual structure of the photon for 0.1 < P^2 < 1.0 GeV^2. The results are compared to Monte Carlo models using different descriptions of the P^2 suppression of the photon.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: To be submitted to the conference and listed on http://opal.web.cern.ch/Opal/pubs/publications.html
Notes:Also submitted to PA-03 and PL-11, Hard processes; abstract 256
The reaction e+e- --> e+e- pi0 X is analysed using data collected with the L3 detector at LEP, at centre-of-mass energies from 189 GeV to 202 GeV for a total integrated luminosity of 410 pb-1. The differential cross-section as a function of the transverse momentum Pt is measured in the diffractive, low Pt region and in the perturbative QCD region, with Pt between 2 GeV and 7 GeV. The differential cross-section is also studied as a function of the pseudorapidity eta for several Pt intervals. The results are well represented by an exponential fit at low Pt. At high Pt the cross-sections are compared to perturbative next-to-leading order QCD calculations
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:in preparation
The reaction e+e- --->e+e- gamma*gamma* --> e+e- hadrons is analysed for quasi-real photons using data collected by the L3 detector during the LEP high energy runs at center-of-mass energies from 189 GeV to 202 GeV . Results on the total cross sections e+e- -->e+e- hadrons and gamma-gamma --> hadrons are given in the interval with W(gamma-gamma) between 5 GeV and 165 GeV. The centre-of-mass energy dependence of the two-photon cross section is described using the universal Regge parametrisation. We observe a steeper rise with W(gamma-gamma) as compared to hadron-hadron cross sections. The data are also compared to the expectations of different theoretical models.
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:in preparation
The H_q moments derived from the charged-particle multiplicity distribution are known to exhibit quasi-oscillations when plotted versus the order of the moment. This behaviour is predicted by the NNLLA of perturbative QCD for the parton level and, under the assumption of LPHD, also for the hadron level. Using the jet multiplicity distributions, obtained from the Cambridge jet algorithm, in order to vary the dependence on the LPHD hypothesis, we find that at our energy the oscillations only appear for non-perturbative scales. Since the weak b-decay is known to distort the multiplicity distribution and NNLLA is based on massless quarks, the analysis is repeated for both tagged light-quark and b-quark samples. In addition, the mean and other low-order moments of the multiplicity distribution have been measured.
Authors:L3 Collaboration
Proposed speaker: L3 speaker
Contact person:Simonetta Gentile
(CERN),
Simonetta.Gentile@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:in preparation
The muon pair production in the process e+e- ---> e+e-m+mu- is studied, using the data taken at LEP with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb-1. The QED predictions have been tested on the whole Q2 range accessible at LEP1 (from several units to several hundred GeV**2/c**4) by comparing experimental distributions of observables to those resulting from a Monte Carlo simulation using various generators. Selected events are used to extract the leptonic photon structure function F_2. Azimuthal correlations are studied to measure additional structure functions F_A and F_B, which originate from interference terms of the scattering amplitudes. They are found to be significantly different from zero and consistent with QED predictions.
Authors:DELPHI Collaboration
Proposed speaker:
Contact person:Clara Matteuzzi
(),
Clara.Matteuzzi@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:Paper will be sent later
The HERMES experiment at the DESY laboratory in Hamburg, Germany, uses a polarised internal gas target in combination with the longitudinally polarised 27.5 GeV positron beam of the HERA accelerator to study the spin structure of the nucleon via deep inelastic lepton-nucleon scattering. Recent inclusive measurements include the spin structure function g1 of the proton and deuteron and the DIS contribution to the generalised GDH integral. Additionally HERMES focuses on semi-inclusive measurements including the flavour separated quark polarisations, the first direct experimental estimation of the polarisation of gluons and the first observation of a spin azimuthal asymmetry in the pion production.
Authors:HERMES-Collaboration
Proposed speaker: A. Gute
Contact person:Klaus Rith
(Universitaet Erlangen),
klaus.rith@physik.uni-erlangen.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) /
Supporting papers:
Notes:5/24/00 TK/TY - Moved from PA-03 to PA-02.
The HERA-B detector is a forward spectrometer with excellent particle identification, covering roughly 90% of the center-of- mass solid angle. Single particle inclusive distributions for Pions, Kaons and Protons are presented as function of XF, Pt and rapidity. The nuclear dependence is studied by comparing data from Carbon, Aluminum, Titanium and Tungsten targets.
Authors:HERA-B Collaboration
Proposed speaker: Ulrich Uwer <uwer@ifh.de>, Speaker's Buero
Contact person:Michael Schmelling
(),
Michael.Schmelling@mpi-hd.mpg.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The cross section of the inclusive production of D*, D+-, D0 mesons in two-photon collisions has been measured by the DELPHI experiment at LEP II energies. The measured cross section values and event distributions are compatible with the QCD calculations with contributions from the resolved processes, which are sensitive to the gluon density in the photon. The total cross section of the charm quark production in two-photon collisions at LEP II energies has been estimated.
Authors:DELPHI Collaboration
Proposed speaker:
Contact person:Clara Matteuzzi
(Universita di Milano),
Clara.Matteuzzi@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:Contributed paper will follow
The eta_c(2980) production in gamma-gamma interactions via its decays into K0_s Kpi and K+K-K+K- has been detected in the data taken with the DELPHI detector at LEP. No direct decay channel eta_c ---> pi+pi-pi+pi- has been observed. The two-photon radiative width of the eta_c charmonium state has been determined providing Gamma_(gamma-gamma)= 16.8+-3.5(stat.)+-2.5(syst.)+-4.5(BR) KeV for eta_c ---> K0_s Kpi decay. A combined value for BR(eta_c ---> (K+K-K+K-)x Gamma_(gamma-gamma) is also determined yielding 0.408+-0.100(stat.)+-0.126(syst.) KeV. Using BR(eta_c ---> K+K-K+K-) taken from PDG the radiation width for K+K-K+K- decay channel is evaluated to be Gamma_(gamma-gamma)=19.4+-4.8(stat.)+-6.0(syst.)+-11.0(BR) KeV.
Authors:DELPHI Collaboration
Proposed speaker:
Contact person:Clara Matteuzzi
(Universita di Milano),
Clara.Matteuzzi@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:Contributed paper will follow
As an example of axial-anomaly-dominated processes of pseudoscalar mesons, the presently experimentally interesting form factor for gamma --> pi^+ pi^0 pi^- is calculated as the quark ``box"-amplitude in: 1.)the simple constituent quark loop model and 2.)the coupled Schwinger-Dyson and Bethe-Salpeter approach which (in the chiral and soft limit) reproduces anomalous amplitudes pi^0 --> 2 gamma and gamma --> pi^+ pi^0 pi^- analytically and exactly, a remarkable feature for a bound-state approach. The form factors for finite transferred momenta obtained in these two approaches are compared with the scarce already available data and with the form factors predicted by the vector meson dominance and chiral perturbation theory.
Authors:Dubravko Klabucar and Bojan Bistrovic
Proposed speaker: Dubravko Klabucar
Contact person:Dubravko Klabucar
(Zagreb University),
klabucar@phy.hr
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: B. Bistrovic and D. Klabucar, Phys. Lett B 478 (2000) 127. (Also available as e-print hep-ph/9912452.) B. Bistrovic and D. Klabucar, Phys. Rev. D 61 (2000) 033006. (Also available as e-print hep-ph/9907515.) D. Kekez, B. Bistrovic and D. Klabucar, Int. J. Mod. Phys. A 14 (1999) 161. (Also available as e-print hep-ph/9809245.)
Notes:
Virtual photon scattering in $e^+e^-$ collisions can result in events with the electron-positron pair at large rapidity separation with hadronic activity in between. The BFKL equation resums large logarithms that dominate the cross section for this process. We report here on a Monte Carlo method for solving the BFKL equation that allows kinematic constraints to be taken into account and show results for $e^+e^-$ collisions.
Authors:Lynne H. Orr and W.J. Stirling
Proposed speaker: Lynne H. Orr
Contact person:Lynne H. Orr
(University of Rochester),
orr@pas.rochester.edu
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Diffractive, exclusive di-jet events produced by 500 GeV/c pions in nuclei were used to measure the A-dependence of production and to make the first direct measurement of the valence-quark momentum distributions in pions. Data on the latter are compared to two limiting predictions for the pion light-cone wave function. The results show that the asymptotic wave function of perturbative QCD describes the data well for Q^2 of 10 (GeV)^2 and above.
Authors:Fermilab E791 collaboration
Proposed speaker: Jeff Appel
Contact person:Milind V Purohit
(Univ of S. Carolina),
e791l@scuch8.psc.sc.edu
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Diffractive photoproduction of D*+- mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 38 pb-1. The measurement was performed for photon-proton centre of mass energies in the range 130 < W < 280 GeV and photon virtuality Q^2 < 1 GeV^2. Diffractive ep collisions were identified by a large rapidity gap in the final state. D*+- mesons were reconstructed in the decay channel D*+ -> D0 pi+ with D0 -> K-pi+ (+c.c.). Integrated and differential cross sections have been measured in a restricted kinematic region and compared with theoretical expectations.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
First measurements are reported of three-jet production in diffractive deep inelastic scattering with the ZEUS detector at HERA using an integrated luminosity of about 30pb-1. The data were measured in the kinematic region Q^2 > 5 GeV^2, 200 < W < 250 GeV, M_X > 23GeV and x_pom < 0.025. The diffractive signal is selected by requiring a large rapidity gap in the outgoing proton direction. Jets are reconstructed in the centre-of-mass system of the observed hadronic final state, with the exclusive-k_T jet-algorithm. The three-jet final-state topology is compared to models for diffraction in deep inelastic scattering.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Open charm production in diffractive DIS has been measured with the ZEUS detector at HERA using an integrated luminosity of 44 pb^-1. Diffractive interactions are identified by the presence of a large rapidity gap in the final state. Charm production is identified by the reconstruction of D*+- (2010) mesons in the decay channels D*+ ->(D0 -> K- pi+) pi+_s (+c.c.) and D*+ -> (D0 -> K- pi+ pi+ pi-) pi+_s (+c.c.). The fraction of DIS D*+- events produced diffractively is found to be sizeable. Differential cross sections in several kinematic variables are compared with the predictions of phenomenological models.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The diffractive dissociation of virtual photons with Q^2 < 1 GeV^2, gamma* p --> X p, has been measured in ep interactions with the ZEUS detector at HERA. For a subsample of the data, the scattered proton was measured with the Leading Proton Spectrometer. The diffractive cross section is presented as a function of Q2, W, M_X, beta, and the scattered proton momentum, where W and M_X are the photon-proton centre-of-mass energy and the mass of the diffractively dissociated photon, respectively, and beta is the equivalent of Bjorken x for the e-Pomeron interaction.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Characteristics of the hadronic final-state of diffractive DIS events, ep --> epX, were studied with the ZEUS detector at HERA using an integrated luminosity of 13.8 pb-1. The events were tagged by identifying the diffractively scattered proton using the Leading Proton Spectrometer. The hadronic final-state X was studied using energy flow, transverse energy flow, x_F, ''seagull'' distributions, sphericity, thrust and thrust angle. Comparison with predictions from Monte Carlo generators suggests that the data may be described by a simple model in which the virtual photon fluctuates into q-qbar and q-qbar-g states coupled to the proton via two-gluon exchange.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The cross section in excess of the QED Compton prediction for the reaction ep -> e gamma p has been measured with the ZEUS detector at HERA using an integrated luminosity of 37 pb^-1. Differential cross sections in the kinematic region 6<Q^2<80 GeV^2 and 40<W<120 GeV are presented as a function of Q^2 and W. The measurements are compared to a leading-order perturbative QCD calculation of the Deeply Virtual Compton Scattering process.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Exclusive photoproduction of J/psi mesons, gamma p --> J/psi p, has been measured in ep collisions with the ZEUS detector at HERA using an integrated luminosity of 36 pb-1. The dependence of the cross section on the photon-proton centre of mass energy, W, is presented as well as the W dependence of the J/psi transverse momentum distributions with respect to the photon direction. The Pomeron trajectory is determined.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Exclusive electroproduction of charmonium in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of 37 pb^-1. The charmonium states were identified using the leptonic decay channels. Cross sections have been measured as a function of Q^2 and W. The angular distribution of the decay leptons has been analysed and compared to the expectations based on the s-channel helicity conservation hypothesis.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Exclusive production of rho mesons has been studied in ep collision with the ZEUS detector at HERA using an integrated luminosity of 37pb-1. The cross section for gamma p -> rho p has been measured for centre-of-mass energies 32<W<160 GeV and for photon virtualities 2<Q^2<50GeV^2. The ratio of the production cross sections, R=sigma_L/sigma_T, for longitudinally (sigma_L) and transversely (sigma_T) polarised virtual photons is determined from the angular distribution of the decay products of the rho. The Q^2, W and t dependence of both the total rho production cross section and R are studied.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The DIS diffractive cross section has been studied in the process ep->eXN, where N is either a proton or a low-mass state, with the ZEUS detector at HERA using an integrated luminosity of 4pb-1. The installation of a forward-plug calorimeter (FPC) increased the rapidity coverage in the proton direction by one unit and enlarged substantially the accessible range in M_X, the mass of the dissociated virtual photon. The cross section has been measured for M_X<25GeV, the hadronic centre-of-mass energy, W, in the range 40GeV<W<245GeV and Q^2 in the range 3GeV^2<Q^2<160GeV^2.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The p_T distribution of leading neutrons in DIS has been measured using a position detector in the Forward Neutron Calorimeter of the ZEUS detector at HERA using an integrated luminosity of 21 pb^-1. The differential distribution dN/dp_T^2 has been measured in bins of x_L, where x_L is the fraction of the proton energy carried by the neutron. The distributions are fitted with an exponential, and the slopes are presented as a function of x_L. The results are compared to models of one pion exchange and also to the slopes for leading proton production.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Leading neutrons are studied in e+p collisions at HERA using the ZEUS detector and its Forward Neutron Calorimeter. The neutrons have production angles < 0.8 mrad and energy fraction, Xl, between 0.2 and 1.0 of the proton energy. The data are binned in the photon virtuality, Q^2: Q^2 < 0.02 GeV^2, 0.1 < Q^2 < 0.74 GeV^2, and 4 < Q^2 < 10,000 GeV^2. Production rates are determined in bins of neutron energy, Q2, and Bjorken x. The semi-inclusive structure function F_2^LN(3)(x,Q2,Xl) is obtained. The data can be interpreted using particle-exchange models in which pion exchange is dominant.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Photoproduction of vector mesons, e+ p --> e+ V N, where N is either the proton or a low-mass dissociated state, has been measured in e^+p interactions with the ZEUS detector at HERA using an integrated luminosity of 24.3 pb^-1. The data were taken at a photon-proton centre-of-mass energy W = 100 GeV and extend up to |t|=12 GeV2, where t is the square of the four-momentum transferred to V. The differential cross section, dsigma/dt, and the results of a decay-angle analysis as a function of t for rho, phi and J/psi production are compared to expectations from phenomenological models.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Elastic and proton-dissociative photoproduction of rho^0, phi and J/psi mesons have been measured in e^+p interactions up to -t=3 GeV^2, where t is the four-momentum-transfer squared at the photon--vector meson vertex, in the ZEUS detector at HERA. The average gamma-proton centre-of-mass energy <W> = 94 GeV. The differential cross sections, dsigma/dt, for rho, phi and J/Psi mesons and the spin-density matrix elements for the rho have been measured. The Pomeron trajectory has been derived from the W dependence of the elastic differential cross-section dsigma/dt for both rho and phi mesons.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The exclusive electroproduction of omega mesons, ep --> e omega p, has been studied in the kinematic range 3< Q2 < 20 GeV2, 40<W <120 GeV and |t|<0.6 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 37.7 pb-1. The reaction ep --> e phi p has also been measured. The cross sections, as well as the ratios sigma(ep --> e omega p)/sigma(ep --> e rho p) and sigma(ep --> e omega p)/sigma(ep -->e phi p), are presented as a function of W and Q2.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
Exclusive electroproduction of rho^0 mesons has been measured using the ZEUS detector at HERA in two Q^2 ranges, 0.25<Q^2<0.85 GeV^2 and 3<Q^2<30 GeV^2. The low-Q^2 data span the range 20<W<90 GeV; the high-Q^2 data cover the 40<W<120 GeV interval. Both samples extend up to four-momentum transfers of |t|=0.6 GeV^2. The distribution in the azimuthal angle between the positron scattering plane and the rho^0 production plane shows a small but significant violation of s-channel helicity conservation, corresponding to the production of longitudinally polarised (i.e. helicity zero) rho^0 mesons from transverse photons. Measurements of the 15 combinations of spin-density matrix elements which completely define the angular distributions are presented and discussed.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
A high statistics measurement of the inclusive deep-inelastic positron-proton scattering cross-section is reported for four-momentum transfers squared 1.5 =< Q^2 =< 150 GeV^2 and for Bjorken-x values 3 x 10^-5 =< x =< 0.2. New H1 instrumentation in the backward region leads to substantially improved systematic precision as compared to previous data. The range of inelasticity y is extended towards low y ~= 0.004, into the region covered by fixed target lepton-nucleon scattering experiments, and towards large y up to 0.89 thereby providing a determination of the longitudinal structure function F L(x,Q^2). A QCD analysis of the H1 deep-inelastic scattering cross-section data allows the gluon distribution xg(x,Q^2) to be derived with improved accuracy at low $x$. The strong interaction coupling constant is obtained in Next-to-Leading Order in a joint determination of xg and alpha s(M Z^2) using H1 e-p and fixed target mu-p inclusive deep inelastic scattering cross-section data.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (043)-945
The cross section of radiative neutral current deep inelastic positron-proton scattering, where a photon is emitted in the direction of the incoming positron, is measured in the kinematic range 0.5 < Q^2 < 15 GeV^2 and 10^-5 < x < 10^-3. The data was recorded in 1997 and corresponds to an integrated luminosity of 15 pb^-1. The variation of the incoming positron energy due to initial state radiation is used to access the longitudinal structure function F L(x,Q^2).
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (045)-943
New preliminary results are presented of the deep inelastic scattering cross section in the Q^2 range 1 to 15 GeV^2 for inelasticities y up to 0.9. Using the cross section derivatives d sigma/d log y, improved data are obtained on the longitudinal structure function F L(x,Q^2). The data were taken by the H1 Collaboration at HERA with positrons of 27.6 GeV energy and protons of 920 GeV energy in a special running period with 3.5 pb^-1 luminosity in December 1999.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (047)-947
First results on the proton structure function F 2(x,Q^2) measured with the VLQ (Very Low Q^2) spectrometer of the H1 experiment at HERA are presented. The VLQ spectrometer which detects electrons at very small scattering angles consists of two identical modules each containing a tungsten-scintillator sandwich calorimeter and a silicon strip tracker. Based on data collected in 1999 the proton structure function F 2(x,Q^2) is presented in the kinematic region 0.1<Q^2<0.4 GeV^2 and 10^(-6) < x < 3*10^(-5).
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (049)-949
An analysis is presented of dijets in photoproduction in ep collisions at HERA where a leading neutron is detected with an energy E n > 400 GeV. Cross sections are measured differentially in jet transverse energy, jet pseudorapidity and x gamma and x pi the momentum fractions of the photon and the postulated exchanged pion entering the hard scattering, respectively. Comparisons are made to predictions based on standard photoproduction processes or based on the one-pion-exchange model. To test factorisation and to investigate the correlation between hadron production in the current and target fragmentation regions, the fraction of dijet events with a leading neutron is compared to the inclusive dijet yield.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (058)
An analysis of two and, for the first time at HERA, three jet production in deep inelastic scattering interactions of the type ep -> eXY is presented, where the component X of the hadronic final state is well separated in rapidity from a leading baryon system with mass M Y < 1.6 GeV. A comprehensive set of single and double differential jet cross sections are measured and the nature of the energy flow not attributed to the dijet system are investigated. The results are used to probe the validity of QCD based calculations and of phenomenological models of diffraction.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (059)
Dijet events with a large rapidity gap between the two highest E t jets are studied in photon-proton collisions at HERA using the inclusive KT algorithm. Rapidity gap events are defined as events in which the sum of the transverse energy of all jets between the two highest E t jet axes is less than E t^cut. Dijet cross sections and the fraction of rapidity gap events are measured differentially as a function of E t^cut, of the rapidity separation between the jets and of the fraction of the proton and photon momentum entering the hard scattering. A significant excess of rapidity gap events is observed and compared with predictions of BFKL based calculations.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (061)
An new, high precision inclusive measurement at HERA of the diffractive deep inelastic scattering process ep -> eXY is presented, where Y is a proton or a low mass proton excitation with M Y < 1.6 GeV. The ratio of diffractive to inclusive DIS cross sections is determined. The dependence of the kinematical variables beta and Q^2 is subjected to a DGLAP fit to extract diffractive parton distributions. A number of QCD based models are compared with the data. The energy dependence of the data is interpreted in terms of a measurement of the effective pomeron intercept alpha pomeron (0).
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (062)
Fragmentation measurements are presented for diffractive deep inelastic ep scattering data in the Breit frame of reference. The evolution of the peak and width of the current hemisphere fragmentation functions and of the slope of the transverse momentum spectrum for charged particles is studied as a function of photon virtuality, Q, and is found to agree with results obtained in non-diffractive deep inelastic scattering. The data are interpreted in a picture where the diffractive final state originates from either a q q bar or a q q bar g partonic configuration.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (063)
Photoproduction processes gamma p -> XY, exhibiting a large gap between the hadronic systems X and Y, is studied at an average centre of mass energy <W> = 98 GeV. The differential cross section is measured as a function of the invariant mass M X of the photon dissociation system and compared to the predictions of a triple Regge decomposition which has been used to describe higher energy HERA and low energy fixed target data.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (064)
A first measurement of the cross section of elastic deeply virtual Compton scattering in positron-proton collisions at HERA is presented. The differential cross section is measured as a function of the squared photon virtuality Q^2, of the gamma* - proton centre-of-mass energy W and other kinematic variables. A clear excess above the expected QED Compton cross section in the e p -> e gamma p reaction is observed at small Q^2 < 10 GeV^2 and W < 100 GeV. The results are found to be in agreement with a prediction based on perturbative QCD.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (065)
An analysis is presented on photoproduction off protons of 820 GeV energy where a leading proton is detected with an energy 540 GeV < E' p < 740 GeV. Cross sections are measured differentially as a function of the energy of the scattered proton E' p in different bins of the gamma-p centre-of-mass energy W in the range 91 GeV < W < 231 GeV. No strong dependence on neither E' p nor W is observed. Using data on deep inelastic scattering with a leading proton, the transition from the photoproduction regime to Q^2 > 0 is studied for different values of E' p.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (066)
The inclusive cross-section for the photoproduction of neutral pions has been measured as a function of the transverse momentum, rapidity and Feynman-x of the pions at an average hadronic centre-of-mass energy of 208 GeV. The pion transverse momentum distribution is described by a power law ansatz. The measured spectra are compared to the QCD-based models PYTHIA and PHOJET. Within the PYTHIA model the data do not favour large values for the intrinsic transverse momentum of the partons in the photon.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (067)
The electroproduction of rho mesons is studied in the process e p -> e rho Y, where the proton dissociates into the hadronic system Y. The skewing of the rho resonance mass shape in the pi^+ pi^- mass distribution is measured as a function of Q^2. The differential cross sections are presented as a function of Q^2, of the centre-of-mass energy W and of the four-momentum transfer squared at the proton vertex, t. An increase in the ratio of proton dissociative to elastic cross sections is observed. Violation of S-channel helicity conservation is confirmed in the proton dissociative rho meson electroproduction process.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (068)
Results are given for the inclusive photoproduction of protons and antiprotons, measured with the H1 detector in ep collisions at HERA. Particle identification based on dE/dx information in the central jet chamber is used for the derivation of cross sections. A non-vanishing asymmetry between baryon and antibaryon production is observed in the photon hemisphere.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (069)
The production of protons and anti-protons is studied in deep-inelastic positron-proton scattering data taken with the H1 detector at the ep collider HERA. Cross sections are presented as function of transverse momentum and pseudorapidity in the hadronic centre of mass system for different intervals of Bjorken-x and four momentum transfer squared Q^2. The yields of protons and anti-protons are compared with the predictions of QCD-based models and used to investigate the universality of baryon production.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (072)
Elastic photoproduction of Heavy Vector Mesons (e^+p -> e^+ V p) at HERA is measured using events with muonic and electronic decays. Elastic psi' meson photoproduction is identified via the direct decay into two leptons and the cascade decay in a J/psi meson and two charged pions. The ratio sigma(psi')/sigma(J/psi) is determined as a function of the hadronic center of mass energy W gammap. In addition the momentum transfer dependence of the cross section is extracted.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes: (086)-985
Cross sections for elastic photoproduction of J/psi and Upsilon mesons are presented. For J/psi mesons the dependence on the photon-proton centre-of-mass energy is analysed in an extended range with respect to previous measurements of 26<=Wgammap<=285 GeV. The measured energy dependence is parameterized as sigma gammap propto W gammap^delta with delta=0.83+-0.07. The differential cross section dsigma/dt for J/psi mesons is derived, its dependence on Wgammap and on t is analysed and the effective trajectory (in terms of Regge theory) is determined to be alpha(t)=(1.27+-0.05)+(0.08+-0.17)*t/GeV^2. Models based on perturbative QCD and on pomeron exchange are compared to the data.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:see hep-ex/0003020 (089)-991
The production of hard di-jet events in photoproduction at HERA is dominated by resolved photon processes in which a parton in the photon with momentum fraction x gamma is scattered from a parton in the proton. These processes are sensitive to the quark and gluon content of the photon. The differential di-jet cross-section dsigma/dlog(x gamma) is presented here, measured in tagged photoproduction at HERA using data taken with the H1 detector, corresponding to an integrated luminosity of 7.2 pb^(-1). Using a restricted data sample at high transverse jet energy, E (T,jet)>6 GeV, the effective parton density f gamma,eff(x gamma) = [q(x gamma) + bar(q)(x gamma) +9/4g(x gamma)] in the photon in leading order QCD is measured down to x gamma=0.05 from which the gluon density in the photon is derived.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:see hep-ex/0003011 (103)-1003
High transverse momentum pi0-mesons have been measured with the H1 detector at HERA in deep-inelastic ep scattering events at low Bjorken-x, down to 4?10^-5. The measurement is performed in a region of small angles with respect to the proton remnant and corresponds to central rapidity in the centre of mass system of the virtual photon and proton, a region expected to be particularly sensitive to QCD effects in hadronic final states. Differential cross-sections for inclusive pi0-meson production are presented as a function of Bjorken-x and the four-momentum transfer squared, Q**2, and as a function of transverse momentum and pseudorapidity. A recent numerical BFKL calculation and predictions from QCD models based on DGLAP parton evolution are compared with the data.
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:see hep-ex/9907030 (106)-1008
Deep-inelastic ep scattering data, taken with the H1 detector at HERA, are used to study the event shape variables thrust, jet broadening, jet mass, C parameter and two kinds of differential two-jet rate. The data cover a large range of the four-momentum transfer Q, which is considered to be the relevant energy scale, between 7 GeV and 100 GeV. The Q dependences of the mean values are compared with second order calculations of perturbative QCD applying power law corrections proportional to 1/Q^p to account for hadronization effects. The concept of power corrections is investigated by fitting simultaneously a non-perturbative parameter alpha (p-1) and the strong coupling constant alpha s
Authors:H1 Collaboration
Proposed speaker: An H1 Speaker
Contact person:Peter Schleper
(DESY),
Peter.Schleper@desy.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:see hep-ex/9912052 (108)-1006
The total photon-proton cross section has been measured in the process e^+p -> e^+ + \gamma^* p -> e^+ + X with the ZEUS detector at HERA. Events were accepted with photon virtuality Q^2 < 0.02 GeV^2, with average \gamma^* p centre-of-mass energy W_{\gamma^* p} = 207 GeV. The data were recorded in a dedicated, systematics-controlled run with an integrated luminosity of 50 nb$^{-1}$.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The proton structure function F_2(x,Q^2) has been measured in e^+p scattering in the kinematic range 0.045 GeV^2 < Q^2 < 0.65 GeV^2 and 6*10^-7 < x < 1*10^-3 with the ZEUS detector at HERA. The uncertainties in F_2 are typically less than 4%. The rise of F_2 at low x is slower than observed in HERA data at higher Q^2 and can be described by Regge theory with a constant logarithmic slope. The dependence of F_2 on Q^2 is stronger than at higher Q^2 values, approaching, at the lowest Q^2 values of this measurement, a region where F_2 becomes nearly proportional to Q^2.
Authors:ZEUS Collaboration
Proposed speaker:
Contact person:Stefan Schlenstedt
(DESY),
stefan.schlenstedt@ifh.de
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers:
Notes:
The total cross-section of the process photon-photon-> bbbar has been measured using data taking by the OPAL detector at LEP at centre-of-mass energies between 189 and 202 GeV. The bbbar events are tagged using semi-leptonic decays into muons. The results are compared with NLO calculations.
Authors:The OPAL collaboration
Proposed speaker:
Contact person:David J Miller
(CERN),
dave.miller@cern.ch
Sessions: PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x ) / PL-12 Soft Interaction Processes ( Low Q2 : diffraction, two-photon and spin structure )
Supporting papers: To be submitted to the conference
Notes:
End of abstracts for PA-02 Soft Interaction Processes ( including diffraction, two-photon, small x )