23 research outputs found
An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment
The ZEUS inclusive differential cross-section data from HERA, for charged and
neutral current processes taken with e+ and e- beams, together with
differential cross-section data on inclusive jet production in e+ p scattering
and dijet production in \gamma p scattering, have been used in a new NLO QCD
analysis to extract the parton distribution functions of the proton. The input
of jet data constrains the gluon and allows an accurate extraction of
\alpha_s(M_Z) at NLO;
\alpha_s(M_Z) = 0.1183 \pm 0.0028(exp.) \pm 0.0008(model)
An additional uncertainty from the choice of scales is estimated as \pm
0.005. This is the first extraction of \alpha_s(M_Z) from HERA data alone.Comment: 37 pages, 14 figures, to be submitted to EPJC. PDFs available at
http://durpdg.dur.ac.uk/hepdata in LHAPDFv
Inclusive jet cross sections and dijet correlations in photoproduction at HERA
Inclusive jet cross sections in photoproduction for events containing a
meson have been measured with the ZEUS detector at HERA using an integrated
luminosity of . The events were required to have a
virtuality of the incoming photon, , of less than 1 GeV, and a
photon-proton centre-of-mass energy in the range . The measurements are compared with next-to-leading-order (NLO) QCD
calculations. Good agreement is found with the NLO calculations over most of
the measured kinematic region. Requiring a second jet in the event allowed a
more detailed comparison with QCD calculations. The measured dijet cross
sections are also compared to Monte Carlo (MC) models which incorporate
leading-order matrix elements followed by parton showers and hadronisation. The
NLO QCD predictions are in general agreement with the data although differences
have been isolated to regions where contributions from higher orders are
expected to be significant. The MC models give a better description than the
NLO predictions of the shape of the measured cross sections.Comment: 43 pages, 12 figures, charm jets ZEU
Study of deep inelastic inclusive and diffractive scattering with the ZEUS forward plug calorimeter
Deep inelastic scattering and its diffractive component, ep -> e'gamma*p
->e'XN, have been studied at HERA with the ZEUS detector using an integrated
luminosity of 4.2 pb-1. The measurement covers a wide range in the gamma*p c.m.
energy W (37 - 245 GeV), photon virtuality Q2 (2.2 - 80 GeV2) and mass Mx. The
diffractive cross section for Mx > 2 GeV rises strongly with W; the rise is
steeper with increasing Q2. The latter observation excludes the description of
diffractive deep inelastic scattering in terms of the exchange of a single
Pomeron. The ratio of diffractive to total cross section is constant as a
function of W, in contradiction to the expectation of Regge phenomenology
combined with a naive extension of the optical theorem to gamma*p scattering.
Above Mx of 8 GeV, the ratio is flat with Q2, indicating a leading-twist
behaviour of the diffractive cross section. The data are also presented in
terms of the diffractive structure function, F2D(3)(beta,xpom,Q2), of the
proton. For fixed beta, the Q2 dependence of xpom F2D(3) changes with xpom in
violation of Regge factorisation. For fixed xpom, xpom F2D(3) rises as beta ->
0, the rise accelerating with increasing Q2. These positive scaling violations
suggest substantial contributions of perturbative effects in the diffractive
DIS cross section.Comment: 87 pages, 25 figure