Dr. Karolos Potamianos

Abstract:

We present a search for the standard model Higgs boson production in association with a W boson in proton-antiproton collisions (pp̄→W ±H→νbb̄) at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately 2.7fb -1. We recorded this data with two kinds of triggers. The first kind required high-p T charged leptons and the second required both missing transverse energy and jets. The search selects events consistent with a signature of a single lepton (e ±/μ ±), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a jet probability tagging method. Kinematic information is fed in an artificial neural network to improve discrimination between signal and background. The search finds that both the observed number of events and the neural network output distributions are consistent with the standard model background expectations, and sets 95% confidence level upper limits on the production cross section times branching ratio. The limits are expressed as a ratio to the standard model production rate. The limits range from 3.6 (4.3 expected) to 61.1 (43.2 expected) for Higgs masses from 100 to 150GeV/c2, respectively. © 2012 American Physical Society.

Abstract:

We present the results of a search for dark matter production in the monojet signature. We analyze a sample of Tevatron pp-bar collisions at sqrt(s)=1.96 TeV corresponding to an integrated luminosity of 6.7/fb recorded by the CDF II detector. In events with large missing transverse energy and one energetic jet, we find good agreement between the standard model prediction and the observed data. We set 90% confidence level upper limits on the dark matter production rate. The limits are translated into bounds on nucleon-dark matter scattering rates which are competitive with current direct detection bounds on spin-independent interaction below a dark matter candidate mass of 5 GeV/c^2, and on spin-dependent interactions up to masses of 200 GeV/c^2.

Abstract:

This Letter describes the current most precise measurement of the $WZ$ production cross section as well as limits on anomalous $WWZ$ couplings at a center-of-mass energy of 1.96 TeV in proton-antiproton collisions for the Collider Detector at Fermilab (CDF). $WZ$ candidates are reconstructed from decays containing three charged leptons and missing energy from a neutrino, where the charged leptons are either electrons or muons. Using data collected by the CDF II detector (7.1 fb$^{-1}$ of integrated luminosity), 63 candidate events are observed with the expected background contributing $8 \pm 1$ events. The measured total cross section $σ(p \bar p \to WZ) = 3.93_{-0.53}^{+0.60}(\text{stat})_{-0.46}^{+0.59}(\text{syst}) $ pb is in good agreement with the standard model prediction of $3.50\pm 0.21$. The same sample is used to set limits on anomalous $WWZ$ couplings.

Abstract:

We report an indirect search for nonstandard model physics using the flavor-changing neutral current decays B→K(*) μ+μ-. We reconstruct the decays and measure their angular distributions, as a function of q2=Mμμ2c2, where M μμ is the dimuon mass, in pp̄ collisions at √s=1.96TeV using a data sample corresponding to an integrated luminosity of 6.8fb-1. The transverse polarization asymmetry AT(2) and the time-reversal-odd charge-and-parity asymmetry Aim are measured for the first time, together with the K* longitudinal polarization fraction FL and the muon forward-backward asymmetry AFB for the decays B0→K*0μ+μ- and B+→K*+μ+μ -. The B→K*μ+μ- forward-backward asymmetry in the most sensitive kinematic regime, 1≤q2<6GeV2/c2, is measured to be AFB=0.29-0.23+0.20(stat) ±0.07(syst), the most precise result to date. No deviations from the standard model predictions are observed. © 2012 American Physical Society.

Abstract:

We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7 - 5.4 fb^-1 of ppbar collisions collected during Run II of the Fermilab Tevatron Collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f0) and right-handed (f+) helicities, we find f0 = 0.722 \pm 0.081 [\pm 0.062 (stat.) \pm 0.052 (syst.)] and f+ = -0.033 \pm 0.046 [\pm 0.034 (stat.) \pm 0.031 (syst.)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f0 = 0.682 \pm 0.057 [\pm 0.035 (stat.) \pm 0.046 (syst.)] and f+ = -0.015\pm0.035 [\pm 0.018 (stat.) \pm 0.030 (syst.)]. The results are consistent with standard model expectations.