Dr Elizabeth Gallas

Abstract:

We report results of a study of the B(s)(0) oscillation frequency using a large sample of B(s)(0) semileptonic decays corresponding to approximately 1 fb(-1) of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider in 2002-2006. The amplitude method gives a lower limit on the B(s)(0) oscillation frequency at 14.8 ps(-1) at the 95% C.L. At delta m(s) = 19 ps(-1), the amplitude deviates from the hypothesis A= 0(1) by 2.5 (1.6) standard deviations, corresponding to a two-sided C.L. of 1% (10%). A likelihood scan over the oscillation frequency, delta m(s), gives a most probable value of 19 ps(-1) and a range of 17 < delta m(s) < 21 ps(-1)at the 90% C.L., assuming Gaussian uncertainties. This is the first direct two-sided bound measured by a single experiment. If delta m(s) lies above 22 ps(-1), then the probability that it would produce a likelihood minimum similar to the one observed in the interval 16-22 ps(-1) is (5.0 +/- 0.3)%.

Abstract:

The results of a search for squarks and gluinos using data from p over(p, ̄) collisions recorded at a center-of-mass energy of 1.96 TeV by the DØ detector at the Fermilab Tevatron Collider are reported. The topologies analyzed consist of acoplanar-jet and multijet events with large missing transverse energy. No evidence for the production of squarks or gluinos was found in a data sample of 310 pb-1. Lower limits of 325 and 241 GeV were derived at the 95% C.L. on the squark and gluino masses, respectively, within the framework of minimal supergravity with tan β = 3, A0 = 0, and μ < 0. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We present the results of a search for the production of an excited state of the muon, μ*, in proton antiproton collisions at s=1.96TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380pb-1. We search for μ* in the process pp̄→μ*μ, with the μ* subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes μ* production by four-fermion contact interactions and μ* decay via electroweak processes, we set a 95% confidence level production cross section upper limit ranging from 0.057 to 0.112 pb, depending on the mass of the excited muon. Choosing the scale for contact interactions to be Λ=1TeV, excited muon masses below 618 GeV are excluded. © 2006 The American Physical Society.

Abstract:

We report on a search for the pair production of second generation scalar leptoquarks ( LQ2) in p over(p, ̄) collisions at the center-of-mass energy sqrt(s) = 1.96   TeV, using data corresponding to an integrated luminosity of 294 ± 19   pb-1 recorded with the DØ detector. No evidence for a leptoquark signal in the LQ2 over(LQ, -)2 → μ q μ q channel has been observed, and upper bounds on the product of cross section times branching fraction were set. This yields lower mass limits of mLQ2 > 247   GeV / c2 for β = B ( LQ2 → μ q ) = 1 and mLQ2 > 182   GeV / c2 for β = 1 / 2. Combining these limits with previous DØ results, the lower limits on the mass of a second generation scalar leptoquark are mLQ2 > 251   GeV / c2 and mLQ2 > 204   GeV / c2 for β = 1 and β = 1 / 2, respectively. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We present a search for the standard model Higgs boson in H→WW(*) decays with e+e-, e±μ, and μ+μ- final states in pp̄ collisions at a center-of-mass energy of s=1.96TeV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300-325pb-1, depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs boson production cross section times branching ratio σ×BR(H→WW(*)) are presented. © 2006 The American Physical Society.