Model-independent measurement of the W-boson helicity in top-quark decays at D0

We present the first model-independent measurement of the helicity of W bosons produced in top quark decays, based on a 1fb-1 sample of candidate tt̄ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron pp̄ Collider. We reconstruct the angle θ* between the momenta of the down-type fermion and the top quark in the W boson rest frame for each top quark decay. A fit of the resulting cos θ* distribution finds that the fraction of longitudinal W bosons f0=0.425±0.166(stat)±0.102(syst) and the fraction of right-handed W bosons f+=0.119±0.090(stat)±0.053(syst), which is consistent at the 30% C.L. with the standard model. © 2008 The American Physical Society

Study of the decay Bs0→Ds(*)Ds(*)

We report a study of the decay Bs0→Ds(*)Ds(*) using a data sample corresponding to 1.3fb-1 of integrated luminosity collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron collider. One Ds(*) meson was partially reconstructed in the decay Ds→ μν, and the other Ds(*) meson was identified using the decay Ds→ π where no attempt was made to distinguish Ds and Ds* states. For the branching fraction Br(Bs0→Ds(*)Ds(*)) we obtain a 90% C.L. range [0.002,0.080] and central value 0.039-0.017+0.019(stat)-0.015+0.016(syst). This was subsequently used to make the most precise estimate of the width difference ΔΓsCP in the Bs0-B̄s0 system: ΔΓsCP/ Γs=0.079-0.035+0.038(stat)-0.030+0.031(syst). © 2007 The American Physical Society

Search for pair production of scalar bottom quarks in pp̄ collisions at s=1.96TeV

A search for direct production of scalar bottom quarks (b) is performed with 310pb-1 of data collected by the D0 experiment in pp̄ collisions at s=1.96TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos (χ∼10), with χ∼10 assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (mb∼, mχ∼10) mass plane, improving significantly upon the results from run I of the Tevatron. © 2006 The American Physical Society