29 research outputs found
Measurement of (anti)deuteron and (anti)proton production in DIS at HERA
The first observation of (anti)deuterons in deep inelastic scattering at HERA
has been made with the ZEUS detector at a centre-of-mass energy of 300--318 GeV
using an integrated luminosity of 120 pb-1. The measurement was performed in
the central rapidity region for transverse momentum per unit of mass in the
range 0.3<p_T/M<0.7. The particle rates have been extracted and interpreted in
terms of the coalescence model. The (anti)deuteron production yield is smaller
than the (anti)proton yield by approximately three orders of magnitude,
consistent with the world measurements.Comment: 26 pages, 9 figures, 5 tables, submitted to Nucl. Phys.
Measurement of dijet photoproduction for events with a leading neutron at HERA
Differential cross sections for dijet photoproduction and this process in
association with a leading neutron, e+ + p -> e+ + jet + jet + X (+ n), have
been measured with the ZEUS detector at HERA using an integrated luminosity of
40 pb-1. The fraction of dijet events with a leading neutron was studied as a
function of different jet and event variables. Single- and double-differential
cross sections are presented as a function of the longitudinal fraction of the
proton momentum carried by the leading neutron, xL, and of its transverse
momentum squared, pT^2. The dijet data are compared to inclusive DIS and
photoproduction results; they are all consistent with a simple pion-exchange
model. The neutron yield as a function of xL was found to depend only on the
fraction of the proton beam energy going into the forward region, independent
of the hard process. No firm conclusion can be drawn on the presence of
rescattering effects.Comment: 40 pages, 18 figure
Deep inelastic inclusive and diffractive scattering at values from 25 to 320 GeV with the ZEUS forward plug calorimeter
Deep inelastic scattering and its diffractive component, , have been studied at HERA with the ZEUS
detector using an integrated luminosity of 52.4 pb. The method has
been used to extract the diffractive contribution. A wide range in the
centre-of-mass energy (37 -- 245 GeV), photon virtuality (20 -- 450
GeV) and mass (0.28 -- 35 GeV) is covered. The diffractive cross
section for GeV rises strongly with , the rise becoming
steeper as increases. The data are also presented in terms of the
diffractive structure function, , of the proton. For fixed
and fixed , \xpom F^{\rm D(3)}_2 shows a strong rise as \xpom \to
0, where \xpom is the fraction of the proton momentum carried by the
Pomeron. For Bjorken-, \xpom F^{\rm D(3)}_2 shows
positive scaling violations, while for
negative scaling violations are observed. The diffractive structure function is
compatible with being leading twist. The data show that Regge factorisation is
broken.Comment: 89 pages, 27 figure
Crystallographic and Structural Analysis of Iron Heterometallic Compounds Part IV: Heteropentameric Compounds
Scaled momentum spectra in deep inelastic scattering at HERA
Charged particle production has been studied in neutral current deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 0.44 fb(-1). Distributions of scaled momenta in the Breit frame are presented for particles in the current fragmentation region. The evolution of these spectra with the photon virtuality, Q(2), is described in the kinematic region 10 < Q(2) < 41000 Ge V-2. Next-to-leading-order and modified leading-log-approximation QCD calculations as well as predictions from Monte Carlo models are compared to the data. The results are also compared to e(+)e(-) annihilation data. The dependences of the pseudorapidity distribution of the particles on Q(2) and on the energy in the gamma p system, W, are presented and interpreted in the context of the hypothesis of limiting fragmentation
Inclusive dijet cross sections in neutral current deep inelastic scattering at HERA
Single- and double-differential inclusive dijet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 374 pb(-1). The measurement was performed at large values of the photon virtuality, Q (2), between 125 and 20 000 GeV2. The jets were reconstructed with the k (T) cluster algorithm in the Breit reference frame and selected by requiring their transverse energies in the Breit frame, E-jet (T,B), to be larger than 8 GeV. In addition, the invariant mass of the dijet system, M-jj,M- was required to be greater than 20 GeV. The cross sections are described by the predictions of next-to-leading-order QCD
A QCD analysis of ZEUS diffractive data
ZEUS inclusive diffractive-cross-section measurements have been used in a DGLAP next-to-leading-order QCD analysis to extract the diffractive parton distribution functions. Data on diffractive dijet production in deep inelastic scattering have also been included to constrain the gluon density. Predictions based on the extracted parton densities are compared to diffractive charm and dijet photoproduction data. (C) 2010 Elsevier B.V. All rights reserved
Production of Z<sup>0</sup> bosons in elastic and quasi-elastic <i>ep</i> collisions at HERA
The production of Z<sup>0</sup> bosons in the reaction ep→eZ<sup>0</sup>p<sup>(⁎)</sup>, where p<sup>(⁎)</sup> stands for a proton or a low-mass nucleon resonance, has been studied in <i>ep</i> collisions at HERA using the ZEUS detector. The analysis is based on a data sample collected between 1996 and 2007, amounting to 496 pb<sup>−1</sup> of integrated luminosity. The Z<sup>0</sup> was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on ηmax<3.0, where η<sub>max</sub> is the maximum pseudorapidity of energy deposits in the calorimeter defined with respect to the proton beam direction. A signal was observed at the Z<sup>0</sup> mass. The cross section of the reaction ep→ eZ<sup>0</sup>p<sup>(⁎)</sup> was measured to be σ(ep→ eZ<sup>0</sup>p<sup>(⁎)</sup>)=0.13±0.06(stat.)±0.01(syst.) pb, in agreement with the Standard Model prediction of 0.16 pb. This is the first measurement of Z<sup>0</sup> production in <i>ep</i> collisions
Multi-lepton production at high transverse momentum at HERA
A search for events containing two or more high-transverse-momentum isolated
leptons has been performed in ep collisions with the ZEUS detector at HERA
using the full collected data sample, corresponding to an integrated luminosity
of 480 pb^{-1}. The number of observed events has been compared with the
prediction from the Standard Model, searching for possible deviations,
especially for multi-lepton events with invariant mass larger than 100 GeV.
Good agreement with the Standard Model has been observed. Total and
differential cross sections for di-lepton production have been measured in a
restricted phase space dominated by photon-photon collisions.Comment: 18 pages, 5 figures. v2: revised version for journal publicatio
Measurement of the t dependence in exclusive photoproduction of (1S) mesons at HERA
The exclusive photoproduction reaction gamma p -> Upsilon(1S) p has been
studied with the ZEUS detector in ep collisions at HERA using an integrated
luminosity of 468 pb^-1. The measurement covers the kinematic range 60<W<220
GeV and Q^2<1 GeV^2, where W is the photon-proton centre-of-mass energy and Q^2
is the photon virtuality. The exponential slope, b, of the t dependence of the
cross section, where t is the squared four-momentum transfer at the proton
vertex, has been measured, yielding b = 4.3 +2.0 -1.3 (stat.) +0.5 -0.6 (syst.)
GeV^-2. This constitutes the first measurement of the t dependence of the gamma
p -> Upsilon(1S) p cross section.Comment: 15 pages, 4 figures; http://dx.doi.org/10.1016/j.physletb.2012.01.00