Dr Elizabeth Gallas

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.

Abstract:

We report results of a study of the Bs0 oscillation frequency using a large sample of Bs0 semileptonic decays corresponding to approximately 1fb-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 Bs0 oscillation frequency at 14.8ps-1 at the 95% C.L. At Δms=19ps-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, Δms, gives a most probable value of 19ps-1 and a range of 17<Δms<21ps-1 at the 90% C.L., assuming Gaussian uncertainties. This is the first direct two-sided bound measured by a single experiment. If Δms lies above 22ps-1, then the probability that it would produce a likelihood minimum similar to the one observed in the interval 16-22ps-1 is (5.0±0.3)%. © 2006 The American Physical Society.

Abstract:

We present a search for supersymmetry in the R-parity violating resonant production and decay of smuons and muon sneutrinos in the channels, 2,3,40. We analyzed 0.38fb-1 of integrated luminosity collected between April 2002 and August 2004 with the D0 detector at the Fermilab Tevatron Collider. The observed number of events is in agreement with the standard model expectation, and we calculate 95% C.L. limits on the slepton production cross section times branching fraction to gaugino plus muon, as a function of slepton and gaugino masses. In the framework of minimal supergravity, we set limits on the coupling parameter, extending significantly previous results obtained in Run I of the Tevatron and at the CERN LEP collider. © 2006 The American Physical Society.