ATLAS

Abstract:

The production of D^{* ±} (2010) mesons in e^± p scattering in the range of exchanged photon virtuality 0.05 < Q² < 0.7   GeV² has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^-1. The decay channels D^{* +} → D⁰ π⁺ with D⁰ → K^- π⁺ 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 Q², inelasticity, y, transverse momentum of the D^* meson, pT (D^*), and pseudorapidity of the D^* meson, η (D^*), have been measured in the kinematic region 0.02 < y < 0.85, 1.5 < pT (D^*) < 9.0   GeV and | η (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. © 2007 Elsevier B.V. All rights reserved.

Abstract:

We search for the technicolor process pp̄→ρT/ ωT→WπT in events containing one electron and two jets, in data corresponding to an integrated luminosity of 390pb-1, recorded by the D0 experiment at the Fermilab Tevatron. Technicolor predicts that technipions πT decay dominantly into bb̄, bc̄, or b̄c, depending on their charge. In these events b and c quarks are identified by their secondary decay vertices within jets. Two analysis methods based on topological variables are presented. Since no excess above the standard model prediction was found, the result is presented as an exclusion in the πT vs ρT mass plane for a given set of model parameters. © 2007 The American Physical Society.

Abstract:

We present a search for electroweak production of single top quarks in the s-channel (pp̄→tb̄+X) and t-channel (pp̄→tqb̄+X) modes. We have analyzed 230pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy of s=1.96TeV. No evidence for a single top quark signal is found. We set 95% confidence level upper limits on the production cross sections, based on binned likelihoods formed from a neural network output. The observed (expected) limits are 6.4 pb (4.5 pb) in the s-channel and 5.0 pb (5.8 pb) in the t-channel. © 2007 The American Physical Society.

Abstract:

Differential inclusive-jet cross sections have been measured for different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q2 > 125   GeV2 with the ZEUS detector at HERA using an integrated luminosity of 81.7 pb-1. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally inclusive mode for different values of the jet radius R. Differential cross sections are presented as functions of Q2 and the jet transverse energy, ET, Bjet. The dependence on R of the inclusive-jet cross section has been measured for Q2 > 125 and 500   GeV2 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 αs (MZ) has been extracted from the measurements of the inclusive-jet cross section d σ / d Q2 with R = 1 for Q2 > 500   GeV2: αs (MZ) = 0.1207 ± 0.0014 (stat .)-0.0033+0.0035 (exp .)-0.0023+0.0022 (th .). The variation of αs with ET, Bjet is in a good agreement with the running of αs as predicted by QCD. © 2007 Elsevier B.V. All rights reserved.