238 research outputs found
K0-Sigma+ Photoproduction with SAPHIR
Preliminary results of the analysis of the reaction p(gamma,K0)Sigma+ are
presented. We show the first measurement of the differential cross section and
much improved data for the total cross section than previous data. The data are
compared with model predictions from different isobar and quark models that
give a good description of p(gamma,K+)Lambda and p(gamma,K+)Sigma0 data in the
same energy range. Results of ChPT describe the data adequately at threshold
while isobar models that include hadronic form factors reproduce the data at
intermediate energies.Comment: 4 pages, Latex2e, 4 postscript figures. Talk given at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97), Brookhaven National Laboratory, USA, October 13-18, 1997. To be
published in Nucl. Phys. A. Revised version due to changes in experimental
dat
Jet production in charged current deep inelastic e⁺p scatteringat HERA
The production rates and substructure of jets have been studied in charged current deep inelastic e⁺p scattering for Q² > 200 GeV² with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb⁻¹. Inclusive jet cross sections are presented for jets with transverse energies E_{T}^{jet} > 5 GeV. Measurements of the mean subjet multiplicity, 〈n_{sbj}〉, of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of α_{s} (M_{z}), determined from 〈n_{sbj}〉 at y_{cut} = 10⁻² for jets with 25 < E_{T}^{jet} < 119 GeV, is α_{s} (M_{z}) = 0.1202 ± 0.0052 (stat.)_{-0.0019}^{+0.0060} (syst.)_{-0.0053}^{+0.0065} (th.). The mean subjet multiplicity as a function of Q² is found to be consistent with that measured in NC DIS
Multijet production in neutral current deep inelastic scattering at HERA and determination of α_{s}
Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson virtualities 10 5 GeV and –1 < η_{LAB}^{jet} < 2.5. Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant α_{s} (M_{z}), determined from the ratio of the trijet to dijet cross sections, is α_{s} (M_{z}) = 0.1179 ± 0.0013 (stat.)_{-0.0046}^{+0.0028}(exp.)_{-0.0046}^{+0.0028}(th.)
High-E_T dijet photoproduction at HERA
The cross section for high-E_T dijet production in photoproduction has been
measured with the ZEUS detector at HERA using an integrated luminosity of 81.8
pb-1. The events were required to have a virtuality of the incoming photon,
Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the
range 142 < W < 293 GeV. Events were selected if at least two jets satisfied
the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV
and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of
the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to
the parton distributions in the photon and proton and effects beyond
next-to-leading order in QCD. Hence these data can be used to constrain further
the parton densities in the proton and photon.Comment: 36 pages, 13 figures, 20 tables, including minor revisions from
referees. Accepted by Phys. Rev.
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
Measurement of event shapes in deep inelastic scattering at HERA
Inclusive event-shape variables have been measured in the current region of
the Breit frame for neutral current deep inelastic ep scattering using an
integrated luminosity of 45.0 pb^-1 collected with the ZEUS detector at HERA.
The variables studied included thrust, jet broadening and invariant jet mass.
The kinematic range covered was 10 < Q^2 < 20,480 GeV^2 and 6.10^-4 < x < 0.6,
where Q^2 is the virtuality of the exchanged boson and x is the Bjorken
variable. The Q dependence of the shape variables has been used in conjunction
with NLO perturbative calculations and the Dokshitzer-Webber non-perturbative
corrections (`power corrections') to investigate the validity of this approach.Comment: 7+25 pages, 6 figure
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
Vector meson production and nucleon resonance analysis in a coupled-channel approach for energies m_N < sqrt(s) < 2 GeV II: photon-induced results
We present a nucleon resonance analysis by simultaneously considering all
pion- and photon-induced experimental data on the final states gamma N, pi N, 2
pi N, eta N, K Lambda, K Sigma, and omega N for energies from the nucleon mass
up to sqrt(s) = 2 GeV. In this analysis we find strong evidence for the
resonances P_{31}(1750), P_{13}(1900), P_{33}(1920), and D_{13}(1950). The
omega N production mechanism is dominated by large P_{11}(1710) and
P_{13}(1900) contributions. In this second part we present the results on the
photoproduction reactions and the electromagnetic properties of the resonances.
The inclusion of all important final states up to sqrt(s) = 2 GeV allows for
estimates on the importance of the individual states for the GDH sum rule.Comment: 41 pages, 26 figures, discussion extended, typos corrected,
references updated, to appear in Phys. Rev.
Beauty photoproduction measured using decays into muons in dijet events in ep collisions at =318 GeV
The photoproduction of beauty 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. 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 beauty production as a function of the
transverse momentum and pseudorapidity of the muon, of the associated jet and
of , 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.Comment: 32 pages, 6 tables, 7 figures Table 6 and Figure 7 revised September
200
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.
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