165 research outputs found

    Scaling violations and determination of alpha(s) from jet production in gamma p interactions at HERA

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    Differential cross sections for jet photoproduction in the reaction ep → e jet X have been measured with the ZEUS detector at HERA using 82.2 pb(-1) of integrated luminosity. Inclusive jet cross sections are presented as a function of the jet transverse energy, E-T(jet), for jets with E-T(jet) gt 17 GeV and pseudorapidity -1 lt eta(jet) lt 2.5, in the gammap centre-of-mass-energy range 142 lt Wgammap lt 293 GeV. Scaled jet invariant cross sections are presented as a function of the dimensionless variable x(T) equivalent to 2E(T)(jet)/W-gammap for (W-gammap) = 180 and 255 GeV: Next-to-leading-order QCD calculations give a good description of the measured differential cross sections in both magnitude and shape. The ratio of scaled jet invariant cross sections at the two (Wgammap) values shows clear non-scaling behaviour. A value for the strong coupling constant of alpha(s) (M-Z) = 0.1224 +/- 0.0001(stat.)(-0.0019)(+0.0022)(exp.)(-0.0042)(+0.0054)(th.) has been extracted from a QCD analysis of the measured dsigma/dE(T)(jet). The variation of sigma(s) with E-T(jet) is in good agreement with the running of sigma(s) as predicted by QCD

    Substructure dependence of jet cross sections at HERA and determination of alpha(S)

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    Jet substructure and differential cross sections for jets produced in the photoproduction and deep inelastic ep scattering regimes have been measured with the ZEUS detector at HERA using an integrated luminosity of 82.2 pb(-1). The substructure of jets has been studied in terms of the jet shape and subjet multiplicity for jets with transverse energies E (jet)/(T) gt 17 GeV. The data are well described by the QCD calculations. The jet shape and subjet multiplicity are used to tag gluon- and quarkjet initiated jets. Jet cross sections as functions of E (jet)/(T) , jet pseudorapidity, the jet-jet scattering angle, dijet invariant mass and the fraction of the photon energy carried by the dijet system are presented for gluon- and quark-tagged jets. The data exhibit the behaviour expected from the underlying parton dynamics. A value of alpha(s) (M-Z) of alpha(s) (M-Z) = 0.1176 +/- 0.0009(stat.) (+0.0009)/(-0.0026) (exp.) (+0.0091)/(-0.0072)(th.) was extracted from the measurements of jet shapes in deep inelastic scattering

    Measurement of subjet multiplicities in neutral current deep inelastic scattering at HERA and determination of alpha(s)

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    The subjet multiplicity has been measured in neutral current e(+) p interactions at Q(2) gt 125 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb(-1). Jets were identified in the laboratory frame using the longitudinally invariant k(T) cluster algorithm. The number of jet-like substructures within jets, known as the subjet multiplicity, is defined as the number of clusters resolved in a jet by reapplying the jet algorithm at a smaller resolution scale y(cut). Measurements of the mean subjet multiplicity, [n(sbj)], for jets with transverse energies E-T,E-jet gt 15 GeV are presented. Next-to-leading-order perturbative QCD calculations describe the measurements well. The value of alpha(s) (M-Z), determined from [n(sbj)] at y(cut) = 10(-2) for jets with 25 lt E-T,E-jet lt 71 GeV, is alpha(s) (M-Z) = 0.1187 +/- 0.0017(stat.)(-0.0009)(+0.0024)(syst.)(- 0.0076)(+0.0093)(th.)

    Observation of K0(s) K0(s) resonances in deep inelastic scattering at HERA

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    Inclusive (KSKS0)-K-0 production in deep inelastic ep scattering at HERA has been studied with the ZEUS detector using an integrated luminosity of 120 pb(-1). Two states are observed at masses of 1537(-8)(+9) MeV and 1726 +/- 7 MeV, as well as an enhancement around 1300 MeV. The state at 1537 MeV is consistent with the well established f'(2)(1525). The state at 1726 MeV may be the glueball candidate f(0)(1710). However, it's width of 38(-14)(+20) MeV is narrower than 125 +/- 10 MeV observed by previous experiments for the f(0)(1710)

    Measurement of high-Q (2) charged current deep inelastic scattering cross sections with a longitudinally polarised positron beam at HERA

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    Measurements of the cross sections for charged current deep inelastic scattering in e+p collisions with a longitudinally polarised positron beam are presented. The measurements are based on a data sample with an integrated luminosity of 132 pb-1 collected with the ZEUS detector at HERA at a centre-of-mass energy of 318 GeV. The total cross section is presented at positive and negative values of the longitudinal polarisation of the positron beams. The single-differential cross-sections dσ/dQ2, dσ/dx and dσ/dy are presented for Q2>200 GeV2. The reduced cross-section σ̃ is presented in the kinematic range 200<Q2<60000 GeV2 and 0.006<x<0.562. The measurements agree well with the predictions of the Standard Model. The results are used to determine a lower limit on the mass of a hypothetical right-handed W boson. © 2010 The Author(s)

    Inclusive jet cross-sections in the Breit frame in neutral current deep inelastic scattering at HERA and determination of alpha(s)

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    Inclusive jet differential cross sections have been measured in neutral current deep inelastic e(+)p scattering for boson virtualities Q(2) gt 125 GeV2. The data were taken using the ZEUS detector at HERA and correspond to an integrated luminosity of 38.6 pb(-1). Jets were identified in the Breit frame using the longitudinally invariant k(T) cluster algorithm. Measurements of differential inclusive jet cross sections a-re presented as functions of jet transverse energy (E-T.jet(B)), jet pseudorapidity and Q(2), for jets with E- T.jet(B) gt 8 GeV. Next-to-leading-order QCD calculations agree well with the measurements both at high Q(2) and high E- T.jet(B). The value of alpha(s) (M-Z), determined from an analysis of dsigma/dQ(2) for Q(2) gt GeV2, is alphas (M-Z) = 0.1212 +/- 0.0017(stat.)(-0.0031)(+0.0023)(syst.)(- 0.0027)(+0.0028)(th.)

    Measurement of the <i>t</i> dependence in exclusive photoproduction of &#978;(1 <i>S</i>) mesons at HERA

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    The exclusive photoproduction reaction γp&#8594;&#978;(1 &lt;i&gt;S&lt;/i&gt;)&lt;i&gt;p&lt;/i&gt; has been studied with the ZEUS detector in &lt;i&gt;ep&lt;/i&gt; collisions at HERA using an integrated luminosity of 468 pb&lt;sup&gt;−1&lt;/sup&gt;. The measurement covers the kinematic range60&#60;W&#60;220 GeV and Q&lt;sup&gt;2&lt;/sup&gt;&#60;1 GeV&lt;sup&gt;2&lt;/sup&gt;, where &lt;i&gt;W&lt;/i&gt; is the photon–proton centre-of-mass energy and Q&lt;sup&gt;2&lt;/sup&gt; is the photon virtuality. The exponential slope, &lt;i&gt;b&lt;/i&gt;, of the &lt;i&gt;t&lt;/i&gt; dependence of the cross section, where &lt;i&gt;t&lt;/i&gt; is the squared four-momentum transfer at the proton vertex, has been measured, yielding b = 4.3{+2.0 =1.3}(stat.){+0.5 -0.6}(syst.) GeV&lt;sup&gt;-2&lt;/sup&gt;. This constitutes the first measurement of the &lt;i&gt;t&lt;/i&gt; dependence of the γp&#8594;&#978;(1 &lt;i&gt;S&lt;/i&gt;)&lt;i&gt;p&lt;/i&gt; cross section

    Inclusive V 0 production cross sections from 920 GeV fixed target proton-nucleus collisions

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    Inclusive differential cross sections dσpA/dxF and dσpA/dp2t for the production of K0S, Λ, and Λ particles are measured at HERA in proton-induced reactions on C, Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to √s = 41.6 GeV in the proton-nucleon system. The ratios of differential cross sections dσpA(K0 S)/dσpA(Λ) and dσpA( ¯ Λ)/dσpA(Λ) are measured to be 6.2 ± 0.5 and 0.66 ± 0.07, respectively, for xF ≈−0.06. No significant dependence upon the target material is observed. Within errors, the slopes of the transverse momentum distributions dσpA/dp2t also show no significant dependence upon the target material. The dependence of the extrapolated total cross sections σpA on the atomic mass A of the target material is discussed, and the deduced cross sections per nucleon σpN are compared with results obtained at other energies

    Evidence for a narrow baryonic state decaying to K0s-p and K0s-pbar in deep inelastic scattering at HERA

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    A resonance search has been made in the K(S)(0)p and K-S(0)(p) over bar invariant-mass spectrum measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb(-1). The search was performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318 GeV for exchanged photon virtuality, Q(2), above 1 GeV2. Recent results from fixed-target experiments give evidence for a narrow baryon resonance decaying to K(+)n and K(S)(0)p, interpreted as a pentaquark. The results presented here support the existence of such state, with a mass of 1521.5 +/- 1.5(stat.)(-1.7)(+2.8)(syst.) MeV and a Gaussian width consistent with the experimental resolution of 2 MeV The signal is visible at high Q(2) and, for Q(2) gt 20 GeV2, contains 221 +/- 48 events. The probability of a similar signal anywhere in the range 1500-1560 MeV arising from fluctuations of the background is below 6 x 10(-5)
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