P. Kooijman

Leading proton production in deep inelastic scattering at HERA

The semi-inclusive reaction e+ p ->e+ X p was studied with the ZEUS detector at HERA using an integrated luminosity of 12.8 pb-1. The final-state proton, which was detected with the ZEUS leading proton spectrometer, carried a large fraction of the incoming proton energy, xL>0.32, and its transverse momentum squared satisfied pT^2<0.5 GeV^2; the exchanged photon virtuality, Q^2, was greater than 3 GeV^2 and the range of the masses of the photon-proton system was 45<W<225 GeV. The leading proton production cross section and rates are presented as a function of xL, pT^2, Q^2 and the Bjorken scaling variable, x.The semi-inclusive reaction e(+)p -> e(+) Xp was studied with the ZEUS detector at HERA with an integrated luminosity of 12.8 pb(-1). The final-state proton, which was detected with the ZEUS leading proton spectrometer, carried a large fraction of the incoming proton energy, x(L) > 0.32, and its transverse momentum squared satisfied p(T)(2) <0.5GeV(2); the exchanged photon virtuality, Q(2), was greater than 3 GeV2 and the range of the masses of the photon-proton system was 45 <W <225GeV. The leading proton production cross section and rates are presented as a function of x(L), p(T)(2), Q(2) and the Bjorken scaling variable, x.

Scaled momentum distributions of charged particles in dijet photoproduction at HERA

The scaled momentum distributions of charged particles in jets have been measured for dijet photoproduction with the ZEUS detector at HERA using an integrated luminosity of 359 pl(-1). The distributions are compared to predictions based on pertubative QCD carried out in the framework of the modified leading-logarithmic approximation (MLLA) and assuming local parton-hadron duality (LPHD). The universal MLLA scale, Lambda(eff), and the LPHD parameter, K-ch, are extracted.The scaled momentum distributions of charged particles in jets have been measured for dijet photoproduction with the ZEUS detector at HERA using an integrated luminosity of 359 pb. The distributions are compared to predictions based on perturbative QCD carried out in the framework of the modified leading-logarithmic approximation (MLLA) and assuming local parton-hadron duality (LPHD). The universal MLLA scale, Λeff , and the LPHD parameter, κ , are extracted. The ZEUS Collaboration S. Chekanov, M. Derrick, S. Magill, B. Musgrave, D. Nicholass, J. Repond, R. Yoshida Argonne National Laboratory, Argonne, Illinois 60439-4815, USA n M.C.K. Mattingly Andrews University, Berrien Springs, Michigan 49104-0380, USA P. Antonioli, G. Bari, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, F. Cindolo, M. Corradi, G. Iacobucci, A. Margotti, R. Nania, A. Polini INFN Bologna, Bologna, Italy e S. Antonelli, M. Basile, M. Bindi, L. Cifarelli, A. Contin, S. De Pasquale, G. Sartorelli, A. Zichichi University and INFN Bologna, Bologna, Italy e D. Bartsch, I. Brock, H. Hartmann, E. Hilger, H.-P. Jakob, M. Jüngst, A.E. Nuncio-Quiroz, E. Paul, U. Samson, V. Schönberg, R. Shehzadi, M. Wlasenko Physikalisches Institut der Universität Bonn, Bonn, Germany b N.H. Brook, G.P. Heath, J.D. Morris H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom m M. Kaur, P. Kaur, I. Singh Panjab University, Department of Physics, Chandigarh, India M. Capua, S. Fazio, A. Mastroberardino, M. Schioppa, G. Susinno, E. Tassi Calabria University, Physics Department and INFN, Cosenza, Italy e J.Y. Kim Chonnam National University, Kwangju, South Korea Z.A. Ibrahim, F. Mohamad Idris, B. Kamaluddin, W.A.T. Wan Abdullah Jabatan Fizik, Universiti Malaya, 50603 Kuala Lumpur, Malaysia r Y. Ning, Z. Ren, F. Sciulli Nevis Laboratories, Columbia University, Irvington on Hudson, New York 10027, USA o J. Chwastowski, A. Eskreys, J. Figiel, A. Galas, K. Olkiewicz, B. Pawlik, P. Stopa, L. Zawiejski The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland i L. Adamczyk, T. Bo ld, I. Grabowska-Bo ld, D. Kisielewska, J. Lukasik, M. Przybycień, L. Suszycki Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Cracow, Poland p

A measurement of the Q(2), W and t dependences of deeply virtual Compton scattering at HERA

Deeply virtual Compton scattering, gamma*p -> gamma p, has been measured in e(+)p collisions at HERA with the ZEUS detector using an integrated luminosity of 61.1 pb(-1). Cross sections are presented as a function of the photon virtuality, Q(2), and photon-proton centre-of-mass energy, W, for a wide region of the phase space, Q(2) > 1.5GeV(2) and 40 < W < 170GeV. A subsample of events in which the scattered proton is measured in the leading proton spectrometer, corresponding to an integrated luminosity of 31.3 pb(-1), is used for the first direct measurement of the differential cross section as a function of t, where t is the square of the four-momentum transfer at the proton vertex.Deeply virtual Compton scattering, γp → γp, has been measured in ep collisions at HERA with the ZEUS detector using an integrated luminosity of 61.1 pb. Cross sections are presented as a function of the photon virtuality, Q, and photon-proton centre-of-mass energy, W , for a wide region of the phase space, Q > 1.5 GeV and 40 < W < 170 GeV. A subsample of events in which the scattered proton is measured in the leading proton spectrometer, corresponding to an integrated luminosity of 31.3 pb, is used for the first direct measurement of the differential cross section as a function of t, where t is the square of the four-momentum transfer at the proton vertex. The ZEUS Collaboration S. Chekanov, M. Derrick, S. Magill, B. Musgrave, D. Nicholass, J. Repond, R. Yoshida Argonne National Laboratory, Argonne, Illinois 60439-4815, USA n M.C.K. Mattingly Andrews University, Berrien Springs, Michigan 49104-0380, USA P. Antonioli, G. Bari, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo F. Cindolo, M. Corradi, G. Iacobucci, A. Margotti, T. Massam, R. Nania, A. Polini INFN Bologna, Bologna, Italy e S. Antonelli, M. Basile, M. Bindi, L. Cifarelli, A. Contin, F. Palmonari, S. De Pasquale, G. Sartorelli, A. Zichichi University and INFN Bologna, Bologna, Italy e D. Bartsch, I. Brock, H. Hartmann, E. Hilger, H.-P. Jakob, M. Jüngst, A.E. Nuncio-Quiroz, E. Paul, U. Samson, V. Schönberg, R. Shehzadi, M. Wlasenko Physikalisches Institut der Universität Bonn, Bonn, Germany b N.H. Brook, G.P. Heath, J.D. Morris H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom m M. Kaur, P. Kaur, I. Singh Panjab University, Department of Physics, Chandigarh, India M. Capua, S. Fazio, A. Mastroberardino, M. Schioppa, G. Susinno, E. Tassi Calabria University, Physics Department and INFN, Cosenza, Italy e J.Y. Kim Chonnam National University, Kwangju, South Korea Z.A. Ibrahim, F. Mohamad Idris, B. Kamaluddin, W.A.T. Wan Abdullah Jabatan Fizik, Universiti Malaya, 50603 Kuala Lumpur, Malaysia r Y. Ning, Z. Ren, F. Sciulli Nevis Laboratories, Columbia University, Irvington on Hudson, New York 10027 o J. Chwastowski, A. Eskreys, J. Figiel, A. Galas, K. Olkiewicz, B. Pawlik, P. Stopa, L. Zawiejski The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland i L. Adamczyk, T. Bo ld, I. Grabowska-Bo ld, D. Kisielewska, J. Lukasik, M. Przybycień, L. Suszycki Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Cracow, Poland p

Measurement of D mesons production in deep inelastic scattering at HERA

Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^{-1}. Charm has been tagged by reconstructing D^{*+}, D^0, D^{+} and D_s^+ (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range p_T(D^{*+},D^0,D^{+}) > 3 GeV, p_T(D_s^+)>2 GeV and |eta(D)| < 1.6 for 1.5 < Q^2 < 1000 GeV^2 and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in p_T(D) and eta(D) in order to determine the open-charm contribution, F_2^{cbar{c}}(x,Q^2), to the proton structure function F_2.Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82pb(-1). Charm has been tagged by reconstructing D*(+), D-0, D+ and D-s(+) (+c.c.) charm mesons. The charm hadrons were measured in the kinematic range p(T)(D*(+), D-0, D+) > 3GeV, p(T)(D-s(+)) > 2GeV and vertical bar eta(D)vertical bar < 1.6 for 1.5 < Q(2) < 1000GeV(2) and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising in to a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in p(T)(D) and eta(D) in order to determine the open-charm contribution, F-2(c (c) over bar) ( x,Q(2)), to the proton structure function F-2.

Leading neutron energy and pT distributions in deep inelastic scattering and photoproduction at HERA

The production of energetic neutrons in ep collisions has been studied with the ZEUS detector at HERA. The neutron energy and p(T)(2) distributions were measured with a forward neutron calorimeter and tracker in a 40 pb(-1) sample of inclusive deep inelastic scattering (DIS) data and a 6 pb(-1) sample of photoproduction data. The neutron yield in photoproduction is suppressed relative to DIS for the lower neutron energies and the neutrons have a steeper p(T)(2)distribution, consistent with the expectation from absorption models. The distributions are compared to HERA measurements of leading protons. The neutron energy and transversemomentum distributions in DIS are compared to Monte Carlo simulations and to the predictions of particle exchange models. Models of pion exchange incorporating absorption and additional secondary meson exchanges give a good description of the data. (c) 2007 Elsevier B.V. All rights reserved.

Exclusive photoproduction of gamma mesons at HERA

The exclusive photoproduction reaction γ p → Υ p has been studied with the ZEUS experiment in ep collisions at HERA using an integrated luminosity of 468 pb. The measurement covers the kinematic range 60 < W < 220 GeV and Q < 1 GeV, where W is the photon-proton centre-of-mass energy and Q is the photon virtuality. These results, which represent the analysis of the full ZEUS data sample for this channel, are compared to predictions based on perturbative QCD. The ZEUS Collaboration S. Chekanov, M. Derrick, S. Magill, B. Musgrave, D. Nicholass, J. Repond, R. Yoshida Argonne National Laboratory, Argonne, Illinois 60439-4815, USA n M.C.K. Mattingly Andrews University, Berrien Springs, Michigan 49104-0380, USA P. Antonioli, G. Bari, L. Bellagamba, D. Boscherini, G. Bruni, F. Cindolo, M. Corradi, G. Iacobucci, A. Margotti, R. Nania, A. Polini INFN Bologna, Bologna, Italy e S. Antonelli, M. Basile, M. Bindi, L. Cifarelli, A. Contin, S. De Pasquale, G. Sartorelli, A. Zichichi University and INFN Bologna, Bologna, Italy e D. Bartsch, I. Brock, H. Hartmann, E. Hilger, H.-P. Jakob, M. Jüngst, A.E. Nuncio-Quiroz, E. Paul, U. Samson, V. Schönberg, R. Shehzadi, M. Wlasenko Physikalisches Institut der Universität Bonn, Bonn, Germany b N.H. Brook, G.P. Heath, J.D. Morris H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom m M. Kaur, P. Kaur, I. Singh Panjab University, Department of Physics, Chandigarh, India M. Capua, S. Fazio, A. Mastroberardino, M. Schioppa, G. Susinno, E. Tassi Calabria University, Physics Department and INFN, Cosenza, Italy e J.Y. Kim Chonnam National University, Kwangju, South Korea Z.A. Ibrahim, F. Mohamad Idris, B. Kamaluddin, W.A.T. Wan Abdullah Jabatan Fizik, Universiti Malaya, 50603 Kuala Lumpur, Malaysia r Y. Ning, Z. Ren, F. Sciulli Nevis Laboratories, Columbia University, Irvington on Hudson, New York 10027, USA o J. Chwastowski, A. Eskreys, J. Figiel, A. Galas, K. Olkiewicz, B. Pawlik, P. Stopa, L. Zawiejski The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland i L. Adamczyk, T. Bo ld, I. Grabowska-Bo ld, D. Kisielewska, J. Lukasik, M. Przybycień, L. Suszycki Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Cracow, Poland p