ATLAS

Abstract:

Correlations between charged particles in deep inelastic e+ p scattering have been studied in the Breit frame with the ZEUS detector at HERA using an integrated luminosity of 6.4pb-1. Short-range correlations are analysed in terms of the angular separation between current-region particles within a cone centred around the virtual photon axis. Long-range correlations between the current and target regions have also been measured. The data support predictions for the scaling behaviour of the angular correlations at high Q2 and for anti-correlations between the current and target regions over a large range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations and Monte Carlo models correctly describe the trends of the data at high Q2, but show quantitative discrepancies. The data show differences between the correlations in deep inelastic scattering and e+e- annihilation.

Abstract:

Bottom-quark production in p¯p collisions at √s=1.8 TeV is studied with 5 pb−1 of data collected in 1995 by the D0 detector at the Fermilab Tevatron Collider. The differential production cross section for b jets in the central rapidity region (|yb|<1) as a function of jet transverse energy is extracted from a muon-tagged jet sample. Within experimental and theoretical uncertainties, D0 results are found to be higher than, but compatible with, next-to-leading-order QCD predictions. © 2000 The American Physical Society.

Abstract:

Events collected by the Collider Detector at Fermilab (CDF) with an energetic jet plus large missing transverse energy can be used to search for physics beyond the standard model. We see no deviations from the expected backgrounds and set upper limits on the production of new processes. We consider in addition the production of light gravitinos and set a limit at 95% F ≥ 217GeV, which excludes gravitino masses smaller than 1.1 × 10−5eV/c2. © 2000 American Physical Society.

Abstract:

The production of D*^± (2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb^-1. The decay channels D*⁺ → D⁰π⁺ (+c.c.), with D⁰ → K^-π⁺ or D⁰ → K^-π^-π⁺π⁺, have been used to identify the D mesons. The e⁺p cross section for inclusive D*^± production with 1 < Q² < 600 GeV² and 0.02 < y < 0.7 is 8.31±0.31(stat.)^+0.30 -0.50 (syst.) nb in the kinematic region 1.5 < pT(D*^±) < 15 GeV and \η(D*^±)\ < 1.5. Differential cross sections are consistent with a next-to-leading-order perturbative-QCD calculation when using charm-fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in pT(D*^±) and η(D*^±) in order to determine the charm contribution, F^cc̄ 2 (x, Q²), to the proton structure function. The ratio F^cc̄ 2/F2 rises from ≃10% at Q² ≃ 1.8GeV² to ≃30% at Q² ≃130GeV² for x values in the range 10^-4 to 10^-3.