Dr Elizabeth Gallas

Abstract:

We present a measurement of the forward-backward charge asymmetry (AFB) in pp̄→Z/γ*+X→e+e-+X events at a center-of-mass energy of 1.96 TeV using 1.1fb-1 of data collected with the D0 detector at the Fermilab Tevatron collider. AFB is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the AFB measurement to extract the effective weak mixing angle sin2θWeff=0.2326±0.0018(stat)±0.0006(syst). © 2008 The American Physical Society.

Abstract:

We present a study of the polarization of the Υ(1S) and Υ(2S) states using a 1.3fb-1 data sample collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron Collider. We measure the polarization parameter α=(σT-2σL)/(σT+2σL), where σT and σL are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum (pTΥ) for the Υ(1S) and Υ(2S). Significant pTΥ-dependent longitudinal polarization is observed for the Υ(1S). A comparison with theoretical models is presented. © 2008 The American Physical Society.

Abstract:

We present a study of the polarization of the Upsilon(1S) and Upsilon(2S) states using a 1.3 fb;{-1} data sample collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron Collider. We measure the polarization parameter alpha=(sigma_{T}-2sigma_{L})/(sigma_{T}+2sigma_{L}), where sigma_{T} and sigma_{L} are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum (p_{T};{Upsilon}) for the Upsilon(1S) and Upsilon(2S). Significant p_{T};{Upsilon}-dependent longitudinal polarization is observed for the Upsilon(1S). A comparison with theoretical models is presented.

Abstract:

We present a search for a narrow-width heavy resonance decaying into top quark pairs (X → t over(t, ̄)) in p over(p, ̄) collisions at sqrt(s) = 1.96 TeV using approximately 0.9 fb-1 of data collected with the DØ detector at the Fermilab Tevatron Collider. This analysis considers t over(t, ̄) candidate events in the lepton plus jets channel with at least one identified b jet and uses the t over(t, ̄) invariant mass distribution to search for evidence of resonant production. We find no evidence for a narrow resonance X decaying to t over(t, ̄). Therefore, we set upper limits on σX ṡ B (X → t over(t, ̄)) for different hypothesized resonance masses using a Bayesian approach. For a Topcolor-assisted technicolor model, the existence of a leptophobic Z′ boson with mass MZ′ < 700 GeV and width ΓZ′ = 0.012 MZ′ can be excluded at the 95% C.L. © 2008 Elsevier B.V.

Abstract:

The process p over(p, ̄) → γ + jet + X is studied using 1.0 fb-1 of data collected by the D0 detector at the Fermilab Tevatron p over(p, ̄) collider at a center-of-mass energy sqrt(s) = 1.96   TeV. Photons are reconstructed in the central rapidity region | yγ | < 1.0 with transverse momenta in the range 30 < pTγ < 400   GeV while jets are reconstructed in either the central | yjet | < 0.8 or forward 1.5 < | yjet | < 2.5 rapidity intervals with pTjet > 15   GeV. The differential cross section d3 σ / d pTγ d yγ d yjet is measured as a function of pTγ in four regions, differing by the relative orientations of the photon and the jet in rapidity. Ratios between the differential cross sections in each region are also presented. Next-to-leading order QCD predictions using different parameterizations of parton distribution functions and theoretical scale choices are compared to the data. The predictions do not simultaneously describe the measured normalization and pTγ dependence of the cross section in the four measured regions.