53 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)

    High-Q2 neutral current cross sections in e+ p deep inelastic scattering at √s = 318 GeV

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    Cross sections for e(+)p neutral current deep inelastic scattering have been measured at a center-of-mass energy of roots=318 GeV with the ZEUS detector at HERA using an integrated luminosity of 63.2 pb(-1). The double-differential cross section, d(2)sigma/dxdQ(2), is presented for 200 GeV2 lt Q(2) lt 30 000 GeV2 and for 0.005 lt x lt 0.65. The single- differential cross sections dsigma/dQ(2), dsigma/dx and dsigma/dy are presented for Q(2) gt 200 GeV2. The effect of Z- boson-exchange is seen in dsigma/dx measured for Q(2) gt 10 000 GeV2. The data presented here were combined with ZEUS e(+)p neutral current data taken at roots=300 GeV and the structure function F-2(em) was extracted. All results agree well with the predictions of the Standard Model

    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)

    Bottom photoproduction measured using decays into muons in dijet events in ep collisions at root s=318 GeV

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    The photoproduction of bottom 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(-1). 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 bottom production as a function of the transverse momentum and pseudorapidity of the muon, of the associated jet and of x(gamma)(jets), 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

    Erratum: Bottom photoproduction measured using decays into muons in dijet events in ep collisions at s=318GeV (Physical Review D - Particles, Fields, Gravitation and Cosmology (2004) 70, (012008))

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    Multijet production in neutral current deep inelastic scattering at HERA and determination of alpha(s)

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    Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson virtualities 10 5 GeV and -1 < ηLABjet < 2.5. Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant αs(MZ), determined from the ratio of the trijet to dijet cross sections, is αs(MZ) = 0.1179 ± 0.0013 (stat.)-0.0046-0.0028 (exp.) -0.0046+0.0064 (th.). © Springer-Verlag / Società Italiana di Fisica 2005
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