Inclusive-jet and dijet differential cross sections have been measured in neutral current deep inelastic ep scattering for exchanged boson virtualities Q2 > 125 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1. Jets were identified in the Breit frame using the kt cluster algorithm. Jet cross sections are presented as functions of several kinematic and jet variables. The results are also presented in different regions of Q2. Next-to-leading-order QCD calculations describe the measurements well. Regions of phase space where the theoretical uncertainties are small have been identified. Measurements in these regions have the potential to constrain the gluon density in the proton when used as inputs to global fits of the proton parton distribution functions.
Dijet cross section as a function of Q**2 in the Breit frame.
Dijet cross section as a function of Bjorken X in the Breit frame.
Dijet cross section as a function of the mean ET of the jets in the Breit frame.
Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 < Q^2 < 100 GeV^2, inelasticity 0.05 < y < 0.7, D meson transverse momenta p_t(D) > 2.5 GeV and pseudorapidity |eta(D)| < 1.5. The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons containing the light quarks u, d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process.
Inclusive D+- electroproduction cross section.
Inclusive D0 electroproduction cross section.
Inclusive D/S+- electroproduction cross section.
Results are presented on the photoproduction of isolated prompt photons, inclusively and associated with jets, in the gamma p center of mass energy range 142 < W < 266 GeV. The cross sections are measured for the transverse momentum range of the photons 5 < E_T^gamma < 10 GeV and for associated jets with E_T^jet > 4.5 GeV. They are measured differentially as a function of E_T^gamma, E_T^jet, the pseudorapidities eta^gamma and eta^jet and estimators of the momentum fractions x_gamma and x_p of the incident photon and proton carried by the constituents participating in the hard process. In order to further investigate the underlying dynamics, the angular correlation between the prompt photon and the jet in the transverse plane is studied. Predictions by perturbative QCD calculations in next to leading order are about 30% below the inclusive prompt photon data after corrections for hadronisation and multiple interactions, but are in reasonable agreement with the results for prompt photons associated with jets. Comparisons with the predictions of the event generators PYTHIA and HERWIG are also presented.
Inclusive prompt photon differential cross section as a function of ET.
Inclusive prompt photon differential cross section as a function of the pseudorapidity.
Prompt photon cross section as a function of the photon ET with an additional jet requirement.
New data are presented on charged particle pseudorapidity distributions for inelastic events produced at c.m. energies\(\sqrt s \)=200 and 900 GeV. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode. The rise of the central density ρ(0) at energies up to\(\sqrt s \)=900 GeV has been studied. A new form of central region scaling is found involving the densityρn(0) for charged multiplicityn, namely that the scaled central densityρn(0)/ρ(0) expressed as a function ofz=n/〈n〉 is independent ofs. Scaling in the fragmentation region holds to 10–20%, and the small amount of scalebreaking observed here could be accommodated within the framework suggested by Wdowcyk and Wolfendale to account for both accelerator and cosmic ray data.
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