Inclusive photoproduction of $\dspm$ in ep collisions at HERA has been measured with the ZEUS detector for photon-proton centre of mass energies in the range \linebreak \wrang and photon virtuality Q~2 < 4 \g2. The cross section $\sigma_{ep \to \ds X} $ integrated over the kinematic region \ptrangand \etarang is {\xsecs}. Differential cross sections as functions of $p_{\perp}~{\ds}$, $\eta~{\ds}$ and W are given. The data are compared with two next-to-leading order perturbative QCD predictions. For a calculation using a massive charm scheme the predicted cross sections are smaller than the measured ones. A recent calculation using a massless charm scheme is in agreement with the data.
Data from the (Kpi)pi channel.
Data from the (Kpipipi)pi channel.
Data from the (Kpi)pi channel.
Photoproduction events which have two or more jets have been studied in the $W_{\gamma p}$ range 135GeV $< W_{\gamma p} <$ 280GeV with the ZEUS detector at HERA. A class of events is observed with little hadronic activity between the jets. The jets are separated by pseudorapidity intervals ($\Delta\eta$) of up to four units and have transverse energies greater than 6GeV. A gap is defined as the absence between the jets of particles with transverse energy greater than 300MeV. The fraction of events containing a gap is measured as a function of \deta. It decreases exponentially as expected for processes in which colour is exchanged between the jets, up to a value of $\Delta\eta \sim 3$, then reaches a constant value of about 0.1. The excess above the exponential fall-off can be interpreted as evidence for hard diffractive scattering via a strongly interacting colour singlet object.
No description provided.
No description provided.
Inclusive jet cross sections for events with a large rapidity gap with respect to the proton direction from the reaction $ep \rightarrow jet \; + \; X$ with quasi-real photons have been measured with the ZEUS detector. The cross sections refer to jets with transverse energies $E_T~{jet}>8$GeV. The data show the characteristics of a diffractive process mediated by pomeron exchange. Assuming that the events are due to the exchange of a pomeron with partonic structure, the quark and gluon content of the pomeron is probed at a scale $\sim (E_T~{jet})~2$. A comparison of the measurements with model predictions based on QCD plus Regge phenomenology requires a contribution of partons with a hard momentum density in the pomeron. A combined analysis of the jet cross sections and recent ZEUS measurements of the diffractive structure function in deep inelastic scattering gives the first experimental evidence for the gluon content of the pomeron in diffractive hard scattering processes. The data indicate that between 30\% and 80\% of the momentum of the pomeron carried by partons is due to hard gluons.
No description provided.
No description provided.
Dijet production by almost real photons has been studied at HERA with the ZEUS detector. Jets have been identified using the cone algorithm. A cut on xg, the fraction of the photon energy participating in the production of the two jets of highest transverse energy, is used to define cross sections sensitive to the parton distributions in the proton and in the photon. The dependence of the dijet cross sections on pseudorapidity has been measured for xg $\ge 0.75$ and xg $< 0.75$. The former is sensitive to the gluon momentum density in the proton. The latter is sensitive to the gluon in the photon. The cross sections are corrected for detector acceptance and compared to leading order QCD calculations.
Direct photon di-jet cross section.. Data are for two (or more) jets.. Second systematic error is due to energy scale uncertainty.
Resolved photon di-jet cross section.. Data are for two (or more) jets.. Second systematic error is due to energy scale uncertainty.
Inclusive jet differential cross sections for the reaction ep → jet + X at Q 2 below 4 GeV 2 have been measured with the ZEUS detector at HERA using an integrated luminosity of 0.55 pb −1 . These cross sections are given in the kinematic region 0.2 < y < 0.85, for jet pseudorapidities in the ep -laboratory range −1 < η jet < 2 and refer to jets at the hadron level with a cone radius of one unit in the η - θ plane. These results correspond to quasi-real photoproduction at centre-of-mass energies in the range 130–270 GeV and, approximately, for jet pseudorapidities in the interval −3 < η jet ( λp CMS) < 0. These measurements cover a new kinematic regime of the partonic structure of the photon, at typical scales up to ∼300 GeV 2 and photon fractional momenta down to x γ ∼ 10 −2 . Leading logarithm parton shower Monte Carlo calculations, which include both resolved and direct processes and use the predictions of currently available parametrisations of the photon parton distributions, describe in general the shape and magnitude of the measured η jet and E t jet distributions.
Second systematic error is uncertainty in the ET scale.
Second systematic error is uncertainty in the ET scale.
Second systematic error is uncertainty in the ET scale.
We present cross section measurements for inclusive jet production in almost-real photon-photon interactions at TRISTAN using the AMY detector. The results are compared with leading-order QCD calculations for different parameterizations of the parton density in the photon.
No description provided.
No description provided.
No description provided.
Forum