Sneha Malde

Abstract:

We report the observation of the bottom, doubly-strange baryon Ωb- through the decay chain Ωb-→J/ψΩ-, where J/ψ→μ+μ-, Ω-→ΛK-, and Λ→pπ-, using 4.2fb-1 of data from pp̄ collisions at s=1.96TeV, and recorded with the Collider Detector at Fermilab. A signal is observed whose probability of arising from a background fluctuation is 4.0×10-8, or 5.5 Gaussian standard deviations. The Ωb- mass is measured to be 6054.4±6. 8(stat)±0.9(syst)MeV/c2. The lifetime of the Ωb- baryon is measured to be 1.13-0.40+0.53(stat)±0.02(syst)ps. In addition, for the Ξb- baryon we measure a mass of 5790.9±2.6(stat)±0.8(syst)MeV/c2 and a lifetime of 1.56-0.25+0.27(stat)±0.02(syst)ps. Under the assumption that the Ξb- and Ωb- are produced with similar kinematic distributions to the Λb0 baryon, we find σ(Ξb-)B(Ξb-→J/ψΞ-) σ(Λb0)B(Λb0→J/ψΛ)=0.167-0.025+0.037(stat) ±0.012(syst) and σ(Ωb-)B(Ωb-→J/ψΩ-) σ(Λb0)B(Λb0→J/ψΛ)=0.045-0.012+0.017(stat) ±0.004(syst) for baryons produced with transverse momentum in the range of 6-20GeV/c. © 2009 The American Physical Society.

Abstract:

We present an analysis of the mass of the X(3872) reconstructed via its decay to J/ψπ+π- using 2.4fb-1 of integrated luminosity from pp̄ collisions at s=1.96TeV, collected with the CDF II detector at the Fermilab Tevatron. The possible existence of two nearby mass states is investigated. Within the limits of our experimental resolution the data are consistent with a single state, and having no evidence for two states we set upper limits on the mass difference between two hypothetical states for different assumed ratios of contributions to the observed peak. For equal contributions, the 95% confidence level upper limit on the mass difference is 3.6MeV/c2. Under the single-state model the X(3872) mass is measured to be 3871.61±0.16(stat)±0. 19(syst)MeV/c2, which is the most precise determination to date. © 2009 The American Physical Society.

Abstract:

We report on a search for the process pp̄→γ+W/Z with W/Z→qq̄ in events containing two jets and a photon at the center-of-mass energy s=1.96TeV, using 184pb-1 of data collected by the CDF II detector. A neural network event selection has been developed to optimize the rejection of the large QCD production background; it is shown that this method gives a significant improvement in both signal-to-noise ratio and signal sensitivity, as compared with an event selection based on conventional cuts. An upper limit is presented for the γ+W/Z production cross section with the W and Z decaying hadronically. © 2009 The American Physical Society.

Abstract:

We present a signature-based search for the anomalous production of events containing a photon, two jets, of which at least one is identified as originating from a b quark, and missing transverse energy (E T). The search uses data corresponding to 2.0fb-1 of integrated luminosity from pp̄ collisions at a center-of-mass energy of s=1.96TeV, collected with the CDF II detector at the Fermilab Tevatron. From 6.69747×106 events with a photon candidate with transverse energy ET>25GeV, we find 617 events with E T>25GeV and two or more jets with ET>15GeV, at least one identified as originating from a b quark, versus an expectation of 607±113 events. Increasing the requirement on E T to 50 GeV, we find 28 events versus an expectation of 30±11 events. We find no indications of non-standard-model phenomena. © 2009 The American Physical Society.

Abstract:

We present the first measurement of the mass of the top quark in a sample of tt̄→ ν̄bb̄qq̄ events (where =e,μ) selected by identifying jets containing a muon candidate from the semileptonic decay of heavy-flavor hadrons (soft muon b tagging). The pp̄ collision data used correspond to an integrated luminosity of 2fb-1 and were collected by the CDF II detector at the Fermilab Tevatron Collider. The measurement is based on a novel technique exploiting the invariant mass of a subset of the decay particles, specifically the lepton from the W boson of the t→Wb decay and the muon from a semileptonic b decay. We fit template histograms, derived from simulation of tt̄ events and a modeling of the background, to the mass distribution observed in the data and measure a top quark mass of 180.5±12.0(stat) ±3.6(syst)GeV/c2, consistent with the current world average value. © 2009 The American Physical Society.