arXiv subjects

ZEUS Collaboration

Publications and source records attributed to ZEUS Collaboration.

222 records · Page 13Linked to original sources

arXiv1995

Measurement of the Cross Section for the Reaction $γp \to \jpsi~p$ with the ZEUS Detector at HERA

This paper reports the cross section measurements for the process ep $\rightarrow$ e~\jpsi~p for $Q^2 < 4$ GeV$^2$ at $\sqrt s = 296$ GeV, based on an integrated luminosity of about 0.5~pb$^{-1}$, using the ZEUS detector. The \jpsi~was detected in its $\rm e^{+}e^{-}$ and $\rm μ^{+}μ^{-}$ decay modes. The photoproduction cross section was measured to be $52^{ \ +7}_{-12}\pm 10$~nb at an average $γ$p centre of mass energy of 67 GeV and $71^{+13}_{-20}\pm 12$~nb at 114 GeV. The significant rise of the cross section compared to lower energy measurements is not in agreement with VDM models, but can be described by QCD inspired models if a rise in the gluon momentum density at low $x$ in the proton is assumed.

hep-ex↗

arXiv1995

Dijet Cross Sections in Photoproduction at HERA

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.

hep-ex↗

arXiv1995

Jet production in high Q^2 deep-inelastic eo scattering at HERA

Two-jet production in deep-inelastic electron-proton scattering has been studied for $160<Q^2<1280$~GeV$^2$, $0.01<x<0.1$ and $0.04<y<0.95$ with the ZEUS detector at HERA. The kinematic properties of the jets and the jet production rates are presented. The partonic scaling variables of the two-jet system and the rate of two-jet production are compared to perturbative next-to-leading order QCD calculations.

hep-ex↗

arXiv1995

Study of D*(2010)+- Production in ep Collisions at HERA

We report the first observation of charmed mesons with the ZEUS detector at HERA using the decay channel ${\rm D}^{*+}\rightarrow (\Do \rightarrow {\rm K}^-π^+)π^+$ (+ c.c.). Clear signals in the mass difference $ΔM$=$M$(D$^*$)--$M$(D$^0)$ as well as in the $M(Kπ)$ distribution at the D$^0$ mass are found. The $ep$ cross section for inclusive \DSpm\ production with $Q^2<4~\GeV^2$ in the $γp$ centre-of-mass energy range $115 < W < 275$ \GeV\ has been determined to be $(32 \pm 7^{+4}_{-7} )$ nb in the kinematic region \mbox{\{$p_T(\DS)\geq $ 1.7 \,\GeV, $|η(\DS)| < 1.5 $\}}. Ex\-tra\-po\-la\-ting outside this region, assuming a mass of the charm quark of 1.5 \GeV, we estimate the $ep$ charm cross section to be $σ(e p \rightarrow c \bar{c}X ) = (0.45 \pm 0.11^{+0.37}_{-0.22}) \, μ{\rm b} $ at \mbox{$\sqrt{s} = 296$}~\GeV\ and $\langle W \rangle = 198$ \GeV. The average $γp$ charm cross section \mbox{$σ(γp \rightarrow c \bar{c}X )$} is found to be \mbox{$(6.3 \pm 2.2^{+6.3}_{-3.0}) \, μ{\rm b} $} at $\langle W \rangle = 163$ \GeV\ and \mbox{$(16.9 \pm 5.2^{+13.9}_{-8.5}) \, μ{\rm b} $} at $\langle W \rangle = 243$ \GeV. The increase of the total charm photoproduction cross section by one order of magnitude with respect to low energy data experiments is well described by QCD NLO calculations using singular gluon distributions in the proton.

hep-ex↗

arXiv1995

Measurement of multiplicity and momentum spectra in the current fragmentation region of the Breit frame at HERA

Charged particle production has been measured in Deep Inelastic Scattering (DIS) events using the ZEUS detector over a large range of $Q^2$ from 10 to $1280 {\rm\ GeV}^2$. The evolution with $Q$ of the charged multiplicity and scaled momentum has been investigated in the current fragmentation region of the Breit frame. The data are used to study QCD \linebreak coherence effects in DIS and are compared with corresponding \ee~data in order to test the universality of quark fragmentation.

hep-ex↗

arXiv1995

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $γp$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.

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