arXiv subjects

The ZEUS Collaboration

Publications and source records attributed to The ZEUS Collaboration.

10 recordsLinked to original sources

arXiv2010

Measurement of D^{+} and Lambda_{c}^{+} production in deep inelastic scattering at HERA

Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 120 pb^{-1}. The hadronic decay channels D^{+} -> K^{0}_{S} pi^{+}, Lambda_{c}^{+} -> p K^{0}_{S} and Lambda_{c}^{+} -> Lambda pi^{+}, and their charge conjugates, were reconstructed. The presence of a neutral strange hadron in the final state reduces the combinatorial background and extends the measured sensitivity into the low transverse momentum region. The kinematic range is 0 < p_{T}(D^{+}, Lambda_{c}^{+}) < 10 GeV, |eta(D^{+}, Lambda_{c}^{+})| < 1.6, 1.5 < Q^{2} < 1000 GeV^{2} and 0.02 < y < 0.7. Inclusive and differential cross sections for the production of D^{+} mesons are compared to next-to-leading-order QCD predictions. The fraction of c quarks hadronising into Lambda_{c}^{+} baryons is extracted.

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arXiv2010

Inclusive-jet cross sections in NC DIS at HERA and a comparison of the kT, anti-kT and SIScone jet algorithms

For the first time, differential inclusive-jet cross sections have been measured in neutral current deep inelastic ep scattering using the anti-kT and SIScone algorithms. The measurements were made for boson virtualities Q^2 > 125 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 82 pb^-1 and the jets were identified in the Breit frame. The performance and suitability of the jet algorithms for their use in hadron-like reactions were investigated by comparing the measurements to those performed with the kT algorithm. Next-to-leading-order QCD calculations give a good description of the measurements. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O(alphas^3) terms. Values of alphas(Mz) were extracted from the data; the results are compatible with and have similar precision to the value extracted from the kT analysis.

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arXiv2009

Measurement of charm and beauty production in deep inelastic ep scattering from decays into muons at HERA

The production of charm and beauty quarks in ep interactions has been measured with the ZEUS detector at HERA for squared four-momentum exchange Q^2>20 GeV^2, using an integrated luminosity of 126 pb^{-1}. Charm and beauty quarks were identified through their decays into muons. Differential cross sections were measured for muon transverse momenta p_T^μ>1.5 GeV and pseudorapidities -1.6<η^μ<2.3, as a function of p_T^μ, η^μ, Q^2 and Bjorken x. The charm and beauty contributions to the proton structure function F_2 were also extracted. The results agree with previous measurements based on independent techniques and are well described by QCD predictions.

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arXiv2002

Exclusive photoproduction of J/psi mesons at HERA

The exclusive photoproduction of J/psi mesons, gamma p->J/psi p, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20<W<290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the muon and the electron decay channels using integrated luminosities of 38 pb^-1 and 55 pb^-1, respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied at the two standard-deviation level. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for |t|<1.8 GeV^2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b=4.15 \pm 0.05 (stat.)^{+0.30}_{-0.18} (syst.) GeV^-2 at W=90 GeV. The effective parameters of the Pomeron trajectory are alphapom(0) = 1.200 \pm 0.009(stat.)^{+0.004}_{-0.010}(syst.) and alphappom= 0.115 \pm 0.018(stat.)^{+0.008}_{-0.015}(syst.) GeV^-2.

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arXiv2001

Properties of hadronic final states in diffractive deep inelastic ep scattering at HERA

Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep -> eXp, were studied in the kinematic range 4 < M_X < 35 GeV, 4 < Q^2 < 150 GeV^2, 70 < W < 250 GeV and 0.0003 < x_pom < 0.03 with the ZEUS detector at HERA using an integrated luminosity of 13.8 pb^{-1}. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state, X, were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow and ``seagull'' distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qqg states at the parton level.

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arXiv1995

Inclusive Charged Particle Distributions in Deep Inelastic Scattering Events at HERA

A measurement of inclusive charged particle distributions in deep inelastic $ep$ scattering for $γ^* p$ centre-of-mass energies $75< W < 175$~GeV and momentum transfer squared $10< Q^2 < 160$~GeV$^2$ from the ZEUS detector at HERA is presented. The differential charged particle rates in the $γ^* p$ centre-of-mass system as a function of the scaled longitudinal momentum, $x_F$, and of the transverse momentum, $p_t^*$ and $<\!\!p_t^{*\,2}\!\!>\,\,$ , as a function of $x_F$, $W$ and $Q^2$ are given. Separate distributions are shown for events with (LRG) and without (NRG) a rapidity gap with respect to the proton direction. The data are compared with results from experiments at lower beam energies, with the naive quark parton model and with parton models including perturbative QCD corrections. The comparison shows the importance of the higher order QCD processes. Significant differences of the inclusive charged particle rates between NRG and LRG events at the same $W$ are observed. The value of $<\!\!p_t^{*\,2}\!\!>\,\,$ for LRG events with a hadronic mass $M_X$, which excludes the forward produced baryonic system, is similar to the $<\!\!p_t^{*\,2}\!\!>\,\,$ value observed in fixed target experiments at $W \approx M_X$.

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arXiv1995

Measurement of the Proton Structure Function ${F_2}$ at low ${x}$ and low ${Q^2}$ at HERA

We report on a measurement of the proton structure function $F_2$ in the range $3.5\times10^{-5}\leq x \leq 4\times10^{-3}$ and 1.5 ${\rm GeV^2} \leq Q^2 \leq15$ ${\rm GeV^2}$ at the $ep$ collider HERA operating at a centre-of-mass energy of $\sqrt{s} = 300$ ${\rm GeV}$. The rise of $F_2$ with decreasing $x$ observed in the previous HERA measurements persists in this lower $x$ and $Q^2$ range. The $Q^2$ evolution of $F_2$, even at the lowest $Q^2$ and $x$ measured, is consistent with perturbative QCD.

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arXiv1995

Rapidity Gaps between Jets in Photoproduction at HERA

Photoproduction events which have two or more jets have been studied in the $W_{γp}$ range 135~GeV $< W_{γp} <$ 280~GeV 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 ($Δη$) of up to four units and have transverse energies greater than 6~GeV. A gap is defined as the absence between the jets of particles with transverse energy greater than 300~MeV. The fraction of events containing a gap is measured as a function of $Δη$. It decreases exponentially as expected for processes in which colour is exchanged between the jets, up to a value of $Δη\sim 3$, 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.

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arXiv1995

Measurement of $α_S$ from Jet Rates in Deep Inelastic Scattering at HERA

Jet production in deep inelastic scattering for $120<Q^2<3600$~GeV$^2$ has been studied using data from an integrated luminosity of 3.2~pb$^{-1}$ collected with the ZEUS detector at HERA. Jets are identified with the JADE algorithm. A cut on the angular distribution of parton emission in the $γ^*$-parton centre-of-mass system minimises the experimental and theoretical uncertainties in the determination of the jet rates. The jet rates, when compared to ${\cal O}$($α_{s}$^2$) perturbative QCD calculations, allow a precise determination of $α_{s}(Q)$ in three $Q^2$-intervals. The values are consistent with a running of $α_{s}(Q)$, as expected from QCD. Extrapolating to $Q=M_{Z^0}$ yields $α_{s}(M_{Z^0}) = 0.117~\pm~0.005~(stat)~^{+0.004}_{-0.005}~(syst_{exp})~ ~{\pm~0.007}~(syst_{theory})$.

hep-ex↗

arXiv1995

Measurement of Elastic $ρ^0$ Photoproduction at HERA

Elastic $ρ^0$ photoproduction has been measured using the ZEUS detector at HERA. Untagged photoproduction events from $ep$ interactions were used to measure the reaction $γp \rightarrow ρ^0 p$ ($ρ^0 \rightarrow π^+ π^-$) at photon-proton centre-of-mass energies between 60 and 80~GeV and $|t|<0.5$~GeV$^2$, where $t$ is the square of the four-momentum transferred at the proton vertex. The differential cross section $dσ/dM_{ππ}$, where $M_{ππ}$ is the invariant mass of the two pions, and the integrated cross section, $σ_{γp\rightarrow ρ^0 p}$, are presented; the latter was measured to be $14.7\pm 0.4~(\mbox{stat.})~\pm2.4~(\mbox{syst.})~μ\mbox{b}$. The differential cross section $dσ/dt$ has an approximately exponential shape; a fit of the type $A^{\prime}_{t} \exp{(-b^{\prime}_{t}|t| + c^{\prime}_{t} t^2)}$ yields a $t$-slope $b^{\prime}_{t}= 9.9~\pm~1.2~(\mbox{stat.})~\pm 1.4~(\mbox{syst.})~μ\mbox{b}$. The results, when compared to low energy data, show a weak energy dependence of both $σ_{γp\rightarrow ρ^0 p}$ and of the $t$-slope. The $ρ^0$ is produced predominantly with transverse polarisation, demonstrating that $s$-channel helicity conservation holds at these energies.

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