Dr Elizabeth Gallas

Abstract:

From an analysis of the decay Bs0→J/ψ, we obtain the width difference between the light and heavy mass eigenstates ΔΓ(ΓL- ΓH)=0.17±0.09(stat)±0.02(syst)ps-1 and the CP-violating phase s=-0.79±0.56(stat)-0.01+0.14(syst). Under the hypothesis of no CP violation (0), we obtain 1/Γ̄=τ̄(Bs0)=1.52±0.08(stat) -0.03+0.01(syst)ps and ΔΓ=0.12-0.10+0.08(stat)±0.02(syst)ps- 1. The data sample corresponds to an integrated luminosity of about 1.1fb-1 accumulated with the D0 detector at the Fermilab Tevatron collider. This is the first direct measurement of the CP-violating mixing phase in the Bs0 system. © 2007 The American Physical Society.

Abstract:

A search for the pair production of scalar top quarks, over(t, ̃), has been performed in 360 pb-1 of data from p over(p, ̄) collisions at a center-of-mass energy of 1.96 TeV, collected by the DØ detector at the Fermilab Tevatron collider. The over(t, ̃) decay mode considered is over(t, ̃) → c over(χ, ̃)10, where over(χ, ̃)10 is the lightest supersymmetric particle. The topology analyzed therefore consists of a pair of acoplanar heavy-flavor jets with missing transverse energy. The data and standard model expectation are in agreement, and a 95% C.L. exclusion domain in the (mover(t, ̃), mover(χ, ̃)10) plane has been determined, extending the domain excluded by previous experiments. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of tt̄ events in the +jets and dilepton decay channels corresponding to an integrated luminosity of 370pb-1 collected by the D0 detector at the Fermilab Tevatron pp̄ Collider at s=1.96TeV. We reconstruct the decay angle θ* for each lepton. By comparing the cos θ* distribution from the data with that for the expected background and signal for various values of f+ (where we assume that the fraction of longitudinally-polarized W bosons has the standard model value of 0.70), we find f+=0.056±0.080(stat)±0.057(syst) (f+<0.23 at 95% C.L.), consistent with the standard model prediction of f+=3.6×10-4. © 2007 The American Physical Society.

Abstract:

We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (tt̄) produced in pp̄ collisions at s=1.96TeV by the Fermilab Tevatron Collider. We use 370pb-1 of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between b- and b̄-quark jets by using the charge and momenta of tracks within the jet cones. The data are consistent with the expected electric charge, |q|=2e/3. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs QQ̄ with |q|=4e/3. We place an upper limit on the fraction of QQ̄ pairs ρ<0.80 at the 90% C.L. © 2007 The American Physical Society.

Abstract:

We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (tt) produced in pp collisions at (square root) s = 1.96 TeV by the Fermilab Tevatron Collider. We use 370 pb;{-1} of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between b- and b-quark jets by using the charge and momenta of tracks within the jet cones. The data are consistent with the expected electric charge, |q|=2e/3. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs QQ with |q|=4e/3. We place an upper limit on the fraction of QQ pairs rho<0.80 at the 90% C.L.