Dr. Karolos Potamianos

Abstract:

We present one additional study of multi-muon events produced at the Fermilab Tevatron collider and recorded by the CDF II detector. We use a data set acquired with a dedicated dimuon trigger and corresponding to an integrated luminosity of 3.9 fb -1. We investigate the distribution of the azimuthal angle between the two trigger muons in events containing at least four additional muon candidates to test the compatibility of these events with originating from known QCD processes. We find that this distribution is markedly different from what is expected from such QCD processes and this observation strongly disfavors the possibility that multi-muon events result from an underestimate of the rate of misidentified muons in ordinary QCD events. © 2012 Elsevier B.V.

Abstract:

In this Letter, we present a precise measurement of the total ZZ production cross section in pp̄ collisions at √s=1.96TeV, using data collected with the CDF II detector corresponding to an integrated luminosity of approximately 6fb-1. The result is obtained by combining separate measurements in the four-charged (′′) and two-charged-lepton and two-neutral-lepton (νν) decay modes of the Z boson pair. The combined measured cross section for pp̄→ZZ is 1.64-0.38+0.44pb. This is the most precise measurement of the ZZ production cross section in 1.96 TeV pp̄ collisions to date. © 2012 American Physical Society.

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.