Inclusive beauty-quark production in two-photon collisions has been measured at LEP using an integrated luminosity of 698 pb-1 collected by the ALEPH detector with sqrt(s) between 130 and 209 GeV. The b quarks were identified using lifetime information. The cross section is found to be sigma(e+ e- --> e+ e- b \bar{b} X) = (5.4 +/- 0.8 (stat) +/- 0.8 (syst)) pb which is consistent with Next-to-Leading Order QCD.
Cross section for the process E+ E- --> E+ E- BQUARK BQUARKBAR X.
The first observation of (anti)deuterons in deep inelastic scattering at HERA has been made with the ZEUS detector at a centre-of-mass energy of 300--318 GeV using an integrated luminosity of 120 pb-1. The measurement was performed in the central rapidity region for transverse momentum per unit of mass in the range 0.3<p_T/M<0.7. The particle rates have been extracted and interpreted in terms of the coalescence model. The (anti)deuteron production yield is smaller than the (anti)proton yield by approximately three orders of magnitude, consistent with the world measurements.
Measured invariant cross section for P production.
Measured invariant cross section for DEUT production.
Measured invariant cross section for PBAR production.
Inclusive jet production is studied in neutral current deep-inelastic positron-proton scattering at large four momentum transfer squared Q^2>150 GeV^2 with the H1 detector at HERA. Single and double differential inclusive jet cross sections are measured as a function of Q^2 and of the transverse energy E_T of the jets in the Breit frame. The measurements are found to be well described by calculations at next-to-leading order in perturbative QCD. The running of the strong coupling is demonstrated and the value of alpha_s(M_Z) is determined. The ratio of the inclusive jet cross section to the inclusive neutral current cross section is also measured and used to extract a precise value for alpha_s(M_Z)=0.1193+/-0.0014(exp.)^{+0.0047}_{-0.0030}(th.)+/-0.0016(pdf).
Double differential cross section as a function of ET integrated over the ET bin range and the Q**2 range 150 to 200 GeV**2.
Double differential cross section as a function of ET integrated over the ET bin range and the Q**2 range 200 to 270 GeV**2.
Double differential cross section as a function of ET integrated over the ET bin range and the Q**2 range 270 to 400 GeV**2.
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^{-1}. Charm has been tagged by reconstructing D^{*+}, D^0, D^{+} and D_s^+ (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range p_T(D^{*+},D^0,D^{+}) > 3 GeV, p_T(D_s^+)>2 GeV and |\eta(D)| < 1.6 for 1.5 < Q^2 < 1000 GeV^2 and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in p_T(D) and \eta(D) in order to determine the open-charm contribution, F_2^{c\bar{c}}(x,Q^2), to the proton structure function F_2.
Production cross section for all D0 mesons, those not originating fom D* decays and those originating from D* decays.
Production cross section for additional D* mesons (not decaying to D0) and all D* mesons.
Production cross section for D+ mesons.
Diffractive photoproduction of D*+/-(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb^{-1}. The D* mesons were reconstructed in the kinematic range: transverse momentum p_T(D*) > 1.9 GeV and pseudorapidity |eta(D*)| < 1.6, using the decay D*+ -> D0 pi+_s followed by D0 -> K- pi+ (+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon-proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q^2 < 1 GeV^2, in two ranges of the Pomeron fractional momentum x_pom < 0.035 and x_pom < 0.01. The relative contribution of diffractive events to the inclusive D*+/-(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.
Total cross section integrated over the given kinematic range.
Ratio of diffractive to inclusive D* cross section.
Differential cross sections for diffractive photoproduction of D*+- mesons as a function of X(NAME=POMERON).
The production of D*+-(2010) mesons in ep scattering in the range of exchanged photon virtuality 0.05 < Q^2 < 0.7 GeV^2 has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1. The decay channels D*+ -> D0 pi+ with D0 -> K- pi+ and corresponding antiparticle decay were used to identify D* mesons and the ZEUS beampipe calorimeter was used to identify the scattered electron. Differential D* cross sections as functions of Q^2, inelasticity, y, transverse momentum of the D* meson, p_T(D*), and pseudorapidity of the D* meson, eta(D*), have been measured in the kinematic region 0.02 < y < 0.85, 1.5 < p_T(D*) < 9.0 GeV and |eta(D*)| < 1.5. The measured differential cross sections are in agreement with two different NLO QCD calculations. The cross sections are also compared to previous ZEUS measurements in the photoproduction and DIS regimes.
Total cross section measurement.. The second DSYS error is due to the uncertainty in the branching ratio.
Measured differential cross section as a function of Q**2.
Measured differential cross section as a function of Y.
The production of energetic neutrons in $ep$ collisions has been studied with the ZEUS detector at HERA. The neutron energy and $p_T^2$ distributions were measured with a forward neutron calorimeter and tracker in a $40 \pb^{-1}$ sample of inclusive deep inelastic scattering (DIS) data and a $6 \pb^{-1}$ sample of photoproduction data. The neutron yield in photoproduction is suppressed relative to DIS for the lower neutron energies and the neutrons have a steeper $p_T^2$ distribution, consistent with the expectation from absorption models. The distributions are compared to HERA measurements of leading protons. The neutron energy and transverse-momentum distributions in DIS are compared to Monte Carlo simulations and to the predictions of particle exchange models. Models of pion exchange incorporating absorption and additional secondary meson exchanges give a good description of the data.
Ratio of leading neutron to inclusive cross sections integrated to the full PT range.
Normalized double differential cross sections for leading neutron production for the full DIS sample. Statistical errors only are given.
Normalized double differential cross sections for leading neutron production for the full DIS sample. Statistical errors only are given.
Differential inclusive-jet cross sections have been measured for different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q^2 > 125 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 81.7 pb^-1. Jets were identified in the Breit frame using the k_T cluster algorithm in the longitudinally inclusive mode for different values of the jet radius R. Differential cross sections are presented as functions of Q^2 and the jet transverse energy, E_T,B^jet. The dependence on R of the inclusive-jet cross section has been measured for Q^2 > 125 and 500 GeV^2 and found to be linear with R in the range studied. Next-to-leading-order QCD calculations give a good description of the measurements for 0.5 <= R <= 1. A value of alpha_s(M_Z) has been extracted from the measurements of the inclusive-jet cross-section dsigma/dQ^2 with R=1 for Q^2 > 500 GeV^2: alpha_s(M_Z) = 0.1207 +- 0.0014 (stat.) -0.0033 +0.0035 (exp.) -0.0023 +0.0022 (th.). The variation of alpha_s with E_T,B^jet is in good agreement with the running of alpha_s as predicted by QCD.
No description provided.
No description provided.
No description provided.
Inclusive D* production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D* meson is investigated. The analysis covers values of photon virtuality 2< Q^2 <=100 GeV^2 and of inelasticity 0.05<= y <= 0.7. Differential cross sections are measured as a function of Q^2 and x and of various D* meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon-gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the k_T-unintegrated gluon distribution of the proton.
Visible cross section for inclusive D*+- production.
Visible cross section for inclusive D*+- production.
Visible cross section for inclusive D*+- production with two jets.
J/Psi production in p+p collisions at sqrt(s) = 200 GeV has been Measured in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) over a rapidity range of -2.2 < y < 2.2 and a transverse momentum range of 0 < pT < 9 GeV/c. The statistics available allow a detailed measurement of both the pT and rapidity distributions and are sufficient to constrain production models. The total cross section times branching ratio determined for J/Psi production is B_{ll} sigma_pp^J/psi = 178 +/- 3(stat) +/- 53(syst) +/- 18(norm) nb.
J/PSI differential cross section, times dilepton branching ratio, versus transverse momentum PT, at mid rapidity : -0.35<y<0.35.
J/PSI differential cross section, times dilepton branching ratio, versus transverse momentum PT, at forward rapidities : absolute value of y belongs to [1.2;2.2].
Mean PT^2 value at mid rapidities : -0.35<y<0.35 The mean PT is obtained with a phenomonological fit of the J/PSI distribution in PT of the form (1/(2*PI*PT))*D(SIG)/DPT = A ( 1+(PT/B)^2)^-6 .The systematic error includes the incertainty from the maximum shape deviation permitted by the point-to-point correlated errors and from allowing the exponent of the fit fonctionto be a free parameter.
Forum