115 research outputs found

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

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    We report the first observation of charmed mesons with the ZEUS detector at HERA using the decay channel D*+ → (D0 → K-π+)π+ (+c.c.). Clear signals in the mass difference ΔM=M(D*)-M(D0) as well as in the M (Kπ) distribution at the D0 mass are found. The ep cross section for inclusive D*± production with Q2 < 4 GeV2 in the γp centre-of-mass energy range 115 < W < 275 GeV has been determined to be (32±7-7+4)nb m the kinematic region {pT(D*) ≥ 1.7 GeV, |η(D*)| < 1-5}. Extrapolating outside this region, assuming a mass of the charm quark of 1.5 GeV, we estimate the ep charm cross section to be σ(ep → cc̄Χ) = (0.45 ± 0.11-0.22+0.37) μb at √s = 296 GeV and 〈W〉 = 198 GeV. The average γp charm cross section σ(γp → cc̄Χ) is found to be (6.3 ± 2.2-3.0+6.3) μb at 〈W〉 = 163 GeV and (16.9 ± 5.2-8.5+13.9) μb at 〈W〉 = 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

    Differential cross-sections of D*+- photoproduction in e p collisions at HERA

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    Inclusive photoproduction of D*± in ep collisions at HERA has been measured with the ZEUS detector for photon-proton centre of mass energies in the range 115 3 GeV and -1.5 < ηD* < 1.0 is (10.6 ± 1.7(stat.) ± 1.61.3 (syst.)) nb. Differential cross sections as functions of pD*⊥, ηD* 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. © 1997 Published by Elsevier Science B.V

    QCD analysis of deep inelastic lepton-hadron scattering in the region of small values of the bjorken parameter x

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    We present the new framework based on BFKL and DGLAP evolution equations in which the leading in(Q(_2)) and in(l/x) terms are treated on equal footing. We introduce a pair of coupled integro-difFerential equations for the quark singlet and the unintegrated gluon distribution. The observable structure functions are calculated using high energy factorisation approach. We also include the sub-leading in (l/x) effects via consistency constraint. We argue that the use of this constraint leads to more stable solution to the Pomeron intercept than that based on the NLO calculation of the BFKL equation alone and generates resummation to all orders of the major part of the subleading in (l/x) effects. The global fit to all available deep inelastic data is performed using a simple parametrisation of the non-perturbative region. We also present the results for the longitudinal structure function and the charm component of the F(_2) structure function. Next; we extend this approach to the low Q(^2) domain. At small distances we use the perturbative approach based on the unified BFKL/DGLAP equations and for large distances we use Vector Meson Dominance Model and, for the higher mass qq states, the additive quark approach. We show the results for the total cross section and for the ratio of the longitudinal and transverse structure functions. Finally, we calculate the dijet production and consider the decorrelation effects in the azimuthal distributions caused by the diffusion in the transverse momentum k(_r) of the exchanged gluon. Using the gluon distribution which is fixed by the fit to the DIS data we are able to make absolute predictions. We show the results for the dF(_r)/dɸ, the total cross section and also the distributions in Q(^2) as well as in the longitudinal momentum fraction of the gluon. Our theoretical predictions are confronted with the measurements made using ZEUS detector at HERA

    Study of D<sup>*</sup> (2010)<sup>±</sup> production in ep collisions at HERA

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    Study of D* (2010)± production in ep collisions at HER

    Measurement of elastic J / psi photoproduction at HERA

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    The reaction a p --> J/psi p has been studied in epsilon p interactions using the ZEUS detector at HERA. The cross section for elastic J/psi photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 J/psi p), is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter delta in the form sigma(ap-->J/psi p) proportional to W-delta yields the value delta=0.92+/-0.14+/-0.10. The differential cross section d sigma/d\t\ is presented over the range \t\ < 1.0 GEV(2) where t is the square of the four-momentum exchanged at the proton vertex. d sigma/d\t\ falls exponentially with a slope parameter of 4.6+/-0.4(-0.6)(+0.4) GEV(-2). The measured decay angular distrubitions are consistent with 8-channel helicity conservation

    MEASUREMENT OF TOTAL AND PARTIAL PHOTON PROTON CROSS-SECTIONS AT 180 GEV CENTER-OF-MASS ENERGY RID C-1693-2008 RID B-9165-2008 RID C-5889-2009 RID A-4818-2008

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    Photon proton cross sections for elastic light vector meson production, sigma(el)gammap, inelastic diffractive production, sigma(d)gammap, non-diffractive production, sigma(nd)gammap, as well as the total cross section, sigma(tot)gammap, have been measured at an average gammap center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are sigma(el)gammap = 18 +/- 7 mub, sigma(d)gammap = 33 +/- 8 mub, sigma(nd)gammap = 91 +/- 11 mub, and sigma(tot)gammap = 143 +/- 17 mub, where the errors include statistical and systematic errors added in quadrature

    Study of charged current e p interactions at Q**2 > 200-Gev**2 with the ZEUS detector at HERA

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    Deep inelastic charged-current reactions have been studied in e(+)p and e(-)p collisions at a center of mass energy of about 300 GeV in the kinematic region Q(2)>200 GeV2 and x>0.006 using the ZEUS detector at HERA, The integrated cross sections for Q(2)>200 GeV2 are found to be sigma(e+p-->)=30.3(-4.2 -2.6)(+5.5 +1.6) pb and sigma(e-p-->upsilon X)=54.7(-9.8 -3.4)(+15.9 +2.8) pb. Differential cross sections have been measures as functions of the variables x, y and Q(2). From the measured differential cross sections d sigma/dQ(2), the W boson mass is determined to be M(W)=79(-7 -4)(+8 +4) GeV. Measured jet rates and transverse energy profiles agree with model predictions, A search for charged-current interactions with a large rapidity gap yielded one candidate event, corresponding to a cross section of sigma(e+p-->)(Q(2)>200 GeV2; eta(max)<2.5)=0.8(-0.7)(+1.8)+/-0.1 pb
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