169 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
High Physics at HERA and Searches for New Particles
Preliminary results from H1 and ZEUS on Deep Inelastic Scattering (DIS) at
high momentum transfer squared are presented. Used are all available data accumulated by the H1 and ZEUS experiments between 1994 and 1997,
corresponding to integrated luminosities of and ,
respectively. The anomalies observed at high in the 1994 to 1996 data
still remain, though with less significance. Since this high domain
represents a new frontier in DIS, the same data are used to search for new
particles possessing direct couplings to lepton-quark pairs. Assuming that the
slight excess of events observed in Neutral Current DIS is due to a statistical
fluctuation, preliminary limits on the production of leptoquarks and of squarks
in R-parity violating MSSM are presented.Comment: 14 pages, 12 figures, uses iopart style files, contribution to the
3rd UK Phenomenology Workshop on HERA Physics, Durham, Sep 199
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
A characteristic plot of pomeron-exchanged processes in diffractive DIS
The dependence of the fractal behaviors of the pomeron induced system in deep
inelastic lepton-nucleon scattering upon the diffractive kinematic variables is
found rather robust and not sensitive to the distinct parameterization of the
pomeron flux factor and structure function. A feasible experimental test of the
phenomenological pomeron-exchanged model based on the fractal measurement in
DESY collider HERA is proposed.Comment: 14 pages, 2 Postscript figure
Factorization in hard diffraction
In this talk, I reviewed the role of factorization in diffraction hard
scattering.Comment: Talk presented at the Ringberg Workshop on ``New Trends in HERA
Physics 2001''. 10 pages, 6 postscript figures. Misprints correcte
Color Glass Condensate and BFKL dynamics in deep inelastic scattering at small x
The proton structure function F_2(x,Q^2) for x < 0.01 and 0.045< Q^2 < 45
GeV^2, measured in the deep inelastic scattering at HERA, can be well described
within the framework of the Color Glass Condensate.Comment: 4 pages, 1 figure, incl. IOP style files. Talk given at the 17th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2004), Oakland, CA USA, 11-17 Jan 200
Jets in deep-inelastic scattering at HERA
Jet cross sections in deep-inelastic scattering over a wide region of phase
space have been measured at HERA. These cross section measurements provide a
thorough test of the implementation of Quantum Chromodynamics in
next-to-leading order (NLO) calculations. They also provide the opportunity to
test the consistency of the gluon distribution in the proton as extracted from
(mainly) inclusive DIS measurements. Comparison of the cross sections with NLO
enables accurate extractions of the strong coupling constant, , to be
made, several of which are reported here.Comment: Talk presented at "New Trends in HERA Physics", Ringberg Workshop,
June 2001. 13pages, 12figure
Rapidity gaps at HERA and the Tevatron from soft colour exchanges
Models based on soft colour exchanges to rearrange colour strings in the
final state provide a general framework for both diffractive and
non-diffractive events in ep and hadron-hadron collisions. We study two such
models and find that they can reproduce rapidity gap data from both HERA and
the Tevatron. We also discuss the influence of parton cascades and multiple
interactions on the results.Comment: 4 pages, 4 EPS figures, presented at UK Phenomenology Workshop on
Collider Physics, Durham. Uses iopart.cl
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