7 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
Dissociation of virtual photons in events with a leading proton at HERA
The ZEUS detector has been used to study dissociation of virtual photons in
events with a leading proton, gamma^* p -> X p, in e^+p collisions at HERA. The
data cover photon virtualities in two ranges, 0.03<Q^2<0.60 GeV^2 and 2<Q^2<100
GeV^2, with M_X>1.5 GeV, where M_X is the mass of the hadronic final state, X.
Events were required to have a leading proton, detected in the ZEUS leading
proton spectrometer, carrying at least 90% of the incoming proton energy. The
cross section is presented as a function of t, the squared four-momentum
transfer at the proton vertex, Phi, the azimuthal angle between the positron
scattering plane and the proton scattering plane, and Q^2. The data are
presented in terms of the diffractive structure function, F_2^D(3). A
next-to-leading-order QCD fit to the higher-Q^2 data set and to previously
published diffractive charm production data is presented
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
Measurement of D mesons production in deep inelastic scattering at HERA
Forward jet cross sections have been measured in neutral current deep inelastic scattering at low Bjorken-x with the ZEUS detector at HERA using an integrated luminosity of 81.8 pb-1. Measurements are presented for inclusive forward jets as well as for forward jets accompanied by a dijet system. The explored phase space, with jet pseudorapidity up to 4.3 is expected to be particularly sensitive to the dynamics of QCD parton evolution at low x. The measurements are compared to fixed-order QCD calculations and to leading-order parton-shower Monte Carlo models. © 2007 Springer-Verlag / Società Italiana di Fisica