Search for supersymmetry with gauge-mediated breaking in diphoton events at D0
Physical Review Letters 94:4 (2005)
Abstract:
We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263 pb-1 of data collected by the DO experiment at the Fermilab Tevatron Collider in 2002-2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-to-lightest SUSY particle. © 2005 The American Physical.Comparison of three-jet events in pp̄ collisions at √s = 1.8 TeV to predictions from a next-to-leading order QCD calculation
Physical Review D - Particles, Fields, Gravitation and Cosmology 71:3 (2005) 032002-1-032002-12
Abstract:
The properties of three-jet events with total transverse energy greater than 320 GeV and individual jet energy greater than 20 GeV have been analyzed and compared to absolute predictions from a next-to-leading order (NLO) perturbative QCD calculation. These data, of integrated luminosity 86 pb -1, were recorded by the CDF Experiment for pp collisions at √s = 1.8 TeV This study tests a model of higher order QCD processes that result in gluon emission and may give some indication of the magnitude of the contribution of processes higher than NLO. The total cross section is measured to be 466 ± 3(stat.)-70 +207(syst.) pb. The differential cross section is furthermore measured for all kinematically accessible regions of the Dalitz plane, including those for which the theoretical prediction is unreliable. While the measured cross section is consistent with the theoretical prediction in magnitude, the two differ somewhat in shape in the Dalitz plane. © 2005 The American Physical Society.Measurement of the J/ψ meson and b-hadron production cross sections in pp̄ collisions at √s = 1960 GeV
Physical Review D - Particles, Fields, Gravitation and Cosmology 71:3 (2005) 032001-1-032001-26
Abstract:
We present a new measurement of the inclusive and differential production cross sections of J/ψ mesons and b hadrons in proton-antiproton collisions at √s = 1960 GeV. The data correspond to an integrated luminosity of 39.7 pb-1 collected by the CDF run II detector. We find the integrated cross section for inclusive J/ψ production for all transverse momenta from 0 to 20 GeV/c in the rapidity range |y| < 0.6 to be 4.08 ± 0.02(Stat)-0.33 +0.36(syst) μb. We separate the fraction of J/ψ events from the decay of the long-lived b hadrons using the lifetime distribution in all events with pT(J/ψ) > 1.25 GeV/c. We find the total cross section for b hadrons, including both hadrons and antihadrons, decaying to J/ψ with transverse momenta greater than 1.25 GeV/c in the rapidity range |y(J/ψ)| < 0.6 is 0.330 ± 0.005(stat) -0.033 +0.036(syst) μb. Using a Monte Carlo simulation of the decay kinematics of b hadrons to all final states containing a J/ψ, we extract the first measurement of the total single b-hadron cross section down to zero transverse momentum at √s = 1960 GeV. We find the total single b-hadron cross section integrated over all transverse momenta for b hadrons in the rapidity range |y| < 0.6 to be 17.6 ± 0.4(stat) -2.3 +2.5(syst) μb. © 2005 The American Physical Society.Measurement of the W boson polarization in top decay at CDF at √s = 1.8 TeV
Physical Review D - Particles, Fields, Gravitation and Cosmology 71:3 (2005) 031101-1-031101-7
Abstract:
The polarization of the W boson in t →Wb decay is unambiguously predicted by the standard model of electroweak interactions and is a powerful test of our understanding of the tbW vertex. We measure this polarization from the invariant mass of the b quark from t → Wb and the lepton from W → lν whose momenta measure the W decay angle and direction of motion, respectively. In this paper we present a measurement of the decay rate (f V+A) of the W produced from the decay of the top quark in the hypothesis of V + A structure of the tWb vertex. We find no evidence for the nonstandard V + A vertex and set a limit on fV+A < 0.80 at 95% confidence level. By combining this result with a complementary observable in the same data, we assign a limit on fv+A < 0.61 at 95% CL. This corresponds to a constraint on the right-handed helicity component of the W polarization of f+ < 0.18 at 95% CL. This limit is the first significant direct constraint on fV+A in top decay. © 2005 The American Physical Society.The FINeSSE Detector
Nuclear and Particle Physics Proceedings Elsevier 139 (2005) 317-322