23 research outputs found
Angular and Current-Target Correlations in Deep Inelastic Scattering at HERA
Correlations between charged particles in deep inelastic ep scattering have
been studied in the Breit frame with the ZEUS detector at HERA using an
integrated luminosity of 6.4 pb-1. Short-range correlations are analysed in
terms of the angular separation between current-region particles within a cone
centred around the virtual photon axis. Long-range correlations between the
current and target regions have also been measured. The data support
predictions for the scaling behaviour of the angular correlations at high Q2
and for anti-correlations between the current and target regions over a large
range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations
and Monte Carlo models correctly describe the trends of the data at high Q2,
but show quantitative discrepancies. The data show differences between the
correlations in deep inelastic scattering and e+e- annihilation.Comment: 26 pages including 10 figures (submitted to Eur. J. Phys. C
Can large scintillators be used for solar-axion searches to test the cosmological axion-photon oscillation proposal?
Solar-axion interaction rates in NaI, CsI and Xe scintillators via the
axio-electric effect were calculated. A table is presented with photoelectric
and axioelectric cross sections, solar-axion fluxes, and the interaction rates
from 2.0 to 10.0 keV. The results imply that annual-modulation data of large
NaI and CsI arrays, and large Xe scintillation chambers, might be made
sensitive enough to probe coupling to photons at levels required to explain
axion-photon oscillation phenomena proposed to explain the survival of
high-energy photons traveling cosmological distances. The DAMAA/LIBRA data are
used to demonstrate the power of the model-independent annual modulation due to
the seasonal variation in the earth sun distance.Comment: 7 pages and no figure
Measurement of inelastic J/psi production in deep inelastic scattering at HERA
The inelastic production of J/psi mesons in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of 109 pb(-1). The J/psi mesons were identified using the decay channel J/psi -> mu(+)mu(-). The measurements were performed in the kinematic range 2 < Q(2) < 80 GeV(2), 50 < W < 250 GeV, 0.2 < z < 0.9 and -1.6 < Y(lab) < 1.3, where Q(2) is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the J/psi meson in the proton rest frame and Ylab is the rapidity of the J/psi in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the k(T)-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement
Bottom photoproduction measured using decays into muons in dijet events in ep collisions at root s=318 GeV
The photoproduction of bottom quarks in events with two jets and a muon has been measured with the ZEUS detector at HERA using an integrated luminosity of 110 pb(-1). The fraction of jets containing b quarks was extracted from the transverse momentum distribution of the muon relative to the closest jet. Differential cross sections for bottom production as a function of the transverse momentum and pseudorapidity of the muon, of the associated jet and of x(gamma)(jets), the fraction of the photon's momentum participating in the hard process, are compared with MC models and QCD predictions made at next-to-leading order. The latter give a good description of the data
Measurement of diffractive photoproduction of vector mesons at large momentum transfer at HERA
Elastic and proton-dissociative photoproduction of , and
vector mesons (, , respectively) have
been measured in e^+p interactions at HERA up to -t=3 GeV, where t is the
four-momentum transfer squared at the photon-vector meson vertex. The analysis
is based on a data sample in which photoproduction reactions were tagged by
detection of the scattered positron in a special-purpose calorimeter. This
limits the photon virtuality, Q^2, to values less than 0.01 GeV, and
selects a average center-of-mass energy of = 94 GeV. Results for
the differential cross sections, d/d, for , and
mesons are presented and compared to the results of recent QCD
calculations. Results are also presented for the t-dependence of the pion-pair
invariant-mass distribution in the mass region and of the spin-density
matrix elements determined from the decay-angle distributions. The Pomeron
trajectory has been derived from measurements of the W dependence of the
elastic differential cross sections d/d for both and
mesons.Comment: 52 pages, including 24 figures and 18 table
Measurement of the spin density matrix elements in exclusive electroproduction of rho0 mesons at HERA
Exclusive electroproduction of rho^0 mesons has been measured using the ZEUS
detector at HERA in two Q^2 ranges, 0.25<Q^2<0.85 GeV^2 and 3<Q^2<30 GeV^2. The
low-Q^2 data span the range 20<W<90 GeV; the high-Q^2 data cover the 40<W<120
GeV interval. Both samples extend up to four-momentum transfers of |t|=0.6
GeV^2. The distribution in the azimuthal angle between the positron scattering
plane and the rho^0 production plane shows a small but significant violation of
s-channel helicity conservation, corresponding to the production of
longitudinally polarised (i.e. helicity zero) rho^0 mesons from transverse
photons. Measurements of the 15 combinations of spin-density matrix elements
which completely define the angular distributions are presented and discussed.Comment: 32 pages, 8 figures. This version has been accepted by The European
Physics Journal C and incorporates the referee's comment
Search for resonances decaying to e+ jet in e+ p interactions at HERA
The e^+ jet invariant mass spectrum produced in the reaction e^+ p -> e^+ X
has been studied at a center-of-mass energy of 300 GeV. The data were collected
using the ZEUS detector operating at the HERA collider, and correspond to an
integrated luminosity of 47.7 pb^{-1}. The observed mass spectrum is in good
agreement with Standard Model expectations up to an e^+ jet mass of 210 GeV.
Above this mass, some excess is seen. The angular distribution of these events
is typical of high-Q^2 neutral current events and does not give convincing
evidence for the presence of a narrow scalar or vector state. Limits are
presented on the product of cross section and branching ratio for such a state
and are interpreted as limits on leptoquark or R-parity-violating squark
production. Specific leptoquark types are ruled out at 95% confidence level for
coupling strength lambda=0.3 for masses between 150 and 280 GeV
Recent photoproduction results from ZEUS
Recent results for inclusive jet cross sections, dijet cross sections and dijet angular distributions are compared with NLO perturbative QCD calculations. The observation of isolated high PT photons (prompt photons) is also reported
F-2(D(3)) measurements at ZEUS
Results on the diffractive structure function F-2(D(3)) in deep inelastic neutral current positron-proton scattering (DIS) have been obtained by the ZEUS collaboration using two different methods. Diffractive interactions are selected by either requiring a small, not exponentially suppressed invariant hadronic mass M-X in the main detector or by detecting a fast proton in the ZEUS leading proton spectrometer (LPS). The results of the two methods are compared
Leading baryons at low x(L) in DIS and photoproduction at ZEUS
Results obtained by the ZEUS collaboration on leading baryon production in the proton fragmentation region are presented. The reaction gamma p --> NX, with N a proton or a neutron, is examined both at low and high photon virtuality