407 research outputs found
Open Charm Production at HERA
Measurements of charmed particle cross sections at HERA in the
photoproduction and deep inelastic regimes are reviewed. The status of the
comparison with perturbative QCD calculations is discussed.Comment: Presented at the Ringberg Workshop on ``New Trends in HERA Physics
2001'' 17-22 June 2001. 12 pages, 11 figure
Production of J/psi Mesons at HERA
Inelastic and diffractive production of J/psi mesons at HERA is reviewed. The
data on inelastic photoproduction are described well within errors by the
Colour Singlet Model in next-to-leading order. A search for colour octet
processes predicted within the NRQCD/factorisation approach is conducted in
many regions of phase space. No unambiguous evidence has been found to date.
Diffractive elastic production of J/psi mesons has been measured in the limit
of photoproduction up to the highest photon proton center of mass energies. The
increase of the cross section is described by pQCD models. At larger Q^2, the W
dependence is found to be similar to that observed in photoproduction. First
analyses of data at high t yield a powerlike dependence on |t|. A LO BFKL
calculation gives a good description of the data.Comment: 14 pages, 12 figures, contribution to Ringberg 200
Lower bounds for open charm and beauty contributions to F_2
On the basis of some peculiar scaling properties of the OPE coefficient
functions, we give the lower bounds for F_2^{c\bar{c}} and F_2^{b\bar{b}}
independently of the properties of the gluon density function. Predictions for
F_2^{b\bar{b}} within reach of HERA are made.Comment: 10 pages, 4 eps figures. Misprints are corrected and comment is
added. To appear in JHE
Structure functions at large x
Structure function data together with other measurements from fixed-target
deep inelastic scattering and hadron-hadron collider experiments which
contribute to our knowledge of the parton density functions are reviewed. The
inclusive cross-section measurements of neutral and charged current
interactions at HERA are presented and their impact on the parton density
functions is discussed. Future prospects for an improved knowledge of the
parton density functions at large x are briefly mentioned.Comment: Invited talk given at the workshop on ``New Trends in HERA Physics
2001'', Ringberg castle, Germany, June 17-22, 200
Heavy Flavour Physics at HERA - a Survey
At the HERA collider at DESY, high energy electron and positron beams
interact with proton beams. A review is presented of the variety of ways in
which these collisions produce final states containing charm and beauty quarks.Comment: 45 pages including 30 figures. Submitted to International Journal of
Modern Physics
Measurement of D^\pm Production in Deep Inelastic ep Scattering with the ZEUS Detector at HERA
Charm production in deep inelastic ep scattering was measured with the ZEUS detector using an integrated luminosity of 354 pb^{-1}. Charm quarks were identified by reconstructing D^{+} mesons in the D^{+} -\u3e K^{-} pi^{+} pi^{+} decay channel. Lifetime information was used to reduce combinatorial background substantially. Differential cross sections were measured in the kinematic region 5 \u3c Q^{2} \u3c 1000 GeV^{2}, 0.02 \u3c y \u3c 0.7, 1.5 \u3c p_{T}(D^{+}) \u3c 15 GeV and |eta(D^{+})| \u3c 1.6, where Q^{2} is the photon virtuality, y is the inelasticity, and p_{T}(D^{+}) and eta(D^{+}) are the transverse momentum and the pseudorapidity of the D^{+} meson, respectively. Next-to-leading-order QCD predictions are compared to the data. The charm contribution, F_{2}^{cc}, to the proton structure-function F_{2} was extracted
Measurement of D^*\pm Production in Deep Inelastic Scattering at HERA
The production of Dâ± mesons in deep inelastic ep scattering has been measured for exchanged photon virtualities 5 \u3c Q2\u3c1000GeV2, using an integrated luminosity of 363 pbâ1 with the ZEUS detector at HERA. Differential cross sectionshave been measured and compared to next-to-leading-order QC D calculations. The cross-sections are used to extract the charm contribution to the protonstructure functions, expressed in terms of the reduced charm cro ss section, ÏcÌcred. Theoretical calculations based on fits to inclusive HERA data are compared to the results
Deep Inelastic Scattering at HERA
Results from the H1 and ZEUS experiments at HERA on deep inelastic scattering
are reviewed. The data lead to a consistent picture of a steep rise in the F_2
structure function and in the gluon density within the proton. Important new
information on the partonic structure of diffraction is emerging from H1 and
ZEUS. The space-like region in which the weak and electromagnetic interactions
become of equal strength is being explored for the first time. A possible
excess of events at high x and Q^2 compared to the expectations of the Standard
Model has been observed in both experiments.Comment: 80 pages, 42 figure
Diffractive charm photoproduction at HERA ep-collider
The cross section of the -meson diffractive photoproduction at the HERA
collider has been calculated in the framework of perturbatively motivated model
for the different kinematic regions. The camparison between the different
Pomeron models has been performed.Comment: 9 pages, 3 figure
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