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Abstract:

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*+, D0, D+ and D+s (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range pT (D* +,D 0,D+) > 3GeV, pT (D+s ) > 2GeV and |η(D)| < 1.6 for 1.5 < Q2 < 1000GeV2 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 pT (D) and η(D) in order to determine the open-charm contribution, Fcc2 (x,Q2), to the proton structure function F2. © SISSA 2007.

Abstract:

The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral current deep inelastic ep scattering using an integrated luminosity of 45 pb^-1 taken with the ZEUS detector. The kinematic range is 1002<8000 GeV ², 0.22 is the virtuality of the exchanged boson, y is the inelasticity and x is the Bjorken variable. The measurements were made in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers, they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary to describe these data. © Springer-Verlag Berlin Heidelberg 2007.

Abstract:

We present a measurement of the top-quark mass in pp̄ collisions at s=1.96TeV which uses events with an inclusive signature of missing transverse energy and jets. The event selection is sensitive to tt̄→W+bW- b̄→lνbqq′b̄ independent of the lepton flavor and results in a large acceptance for W→τν decays. All-hadronic tt̄ decays and events with identified electrons or muons are vetoed to provide a statistically independent sample with respect to all previous measurements. The top-quark mass is inferred from the distribution of the scalar sum of all jet transverse energies and the missing transverse energy. Using 311pb-1 of integrated luminosity recorded by the Collider Detector at Fermilab, we measure a top-quark mass mt=172.3-9.6+10.8(stat)±10.8(syst)GeV/c2. While the uncertainty on mt is larger than that of other measurements, the result is statistically uncorrelated with those of other methods and thus can help to reduce the overall mt uncertainty when combined with other existing measurements. © 2007 The American Physical Society.

Abstract:

We present results of a search at CDF in 929±56pb-1 of pp̄ collisions at 1.96 TeV for the anomalous production of events containing a high-transverse momentum charged lepton (ℓ, either e or μ) and photon (γ), accompanied by missing transverse energy (E T), and/or additional leptons and photons, and jets (X). We use the same selection criteria as in a previous CDF Run I search, but with an order-magnitude larger data set, a higher pp̄ collision energy, and the CDF II detector. We find 163 ℓγE T+X events, compared to an expectation of 150.6±13.0 events. We observe 74 ℓγ+X events, compared to an expectation of 65.1±7.7 events. We find no events similar to the Run I eeγγE T event. © 2007 The American Physical Society.