Dr Elizabeth Gallas

Abstract:

We report on a search for second generation leptoquarks (LQ2) which decay into a muon plus quark in p over(p, ̄) collisions at a center-of-mass energy of sqrt(s) = 1.96   TeV in the D0 detector using an integrated luminosity of about 300 pb-1. No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction β into a quark and a muon was determined for second generation scalar leptoquarks as a function of the leptoquark mass. This result has been combined with a previously published D0 search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark-muon-quark coupling, λ. Assuming λ = 1, lower limits on the mass of a second generation scalar leptoquark coupling to a u quark and a muon are mLQ2 > 274   GeV and mLQ2 > 226   GeV for β = 1 and β = 1 / 2, respectively. © 2007 Elsevier B.V. All rights reserved.

Abstract:

From an analysis of the decay Bs0-->J/psi phi, we obtain the width difference between the light and heavy mass eigenstates DeltaGamma identical with (GammaL-GammaH)=0.17+/-0.09(stat)+/-0.02(syst) ps-1 and the CP-violating phase phis=-0.79+/-0.56(stat)(-0.01)(+0.14)(syst). Under the hypothesis of no CP violation (phis identical with 0), we obtain 1/Gamma=tau(Bs0)=1.52+/-0.08(stat)(-0.03)(+0.01)(syst) ps and DeltaGamma=0.12(-0.10)(+0.08)(stat)+/-0.02(syst) ps-1. The data sample corresponds to an integrated luminosity of about 1.1 fb-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.

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.