Jeff Tseng

Abstract:

We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, Nq and Ng, produced at the Fermilab Tevatron in pp collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of θc = 0:28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = Ejetθc varies in the range from 12 to 25 GeV. At Q = 19:2 GeV, the ratio of multiplicities r = Ng=Nq is found to be 1:64 ± 0:17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations.

Abstract:

We have measured the azimuthal angular correlation of bb̄ production, using 86.5pb-1 of data collected by Collider Detector at Fermilab (CDF) in pp̄ collisions at s=1.8TeV during 1994-1995. In high-energy pp̄ collisions, such as at the Tevatron, bb̄ production can be schematically categorized into three mechanisms. The leading-order (LO) process is "flavor creation," where both b and b̄ quarks substantially participate in the hard scattering and result in a distinct back-to-back signal in final state. The "flavor excitation" and the "gluon splitting" processes, which appear at next-leading-order (NLO), are known to make a comparable contribution to total bb̄ cross section, while providing very different opening angle distributions from the LO process. An azimuthal opening angle between bottom and antibottom, Δ, has been used for the correlation measurement to probe the interaction creating bb̄ pairs. The Δ distribution has been obtained from two different methods. One method measures the Δ between bottom hadrons using events with two reconstructed secondary vertex tags. The other method uses bb̄→(J/ ψX)(X′) events, where the charged lepton () is an electron (e) or a muon (μ), to measure Δ between bottom quarks. The bb̄ purity is determined as a function of Δ by fitting the decay length of the J/ψ and the impact parameter of the. Both methods quantify the contribution from higher-order production mechanisms by the fraction of the bb̄ pairs produced in the same azimuthal hemisphere, ftoward. The measured ftoward values are consistent with both parton shower Monte Carlo and NLO QCD predictions. © 2005 The American Physical Society.

Abstract:

We present a search for ZZ and ZW vector boson pair production in pp̄ collisions at s=1.96TeV using the leptonic decay channels ZZ→llνν, ZZ→lll′l′, and ZW→lll′ν. In a data sample corresponding to an integrated luminosity of 194pb-1 collected with the Collider Detector at Fermilab, 3 candidate events are found with an expected background of 1.0±0.2 events. We set a 95% confidence level upper limit of 15.2pb on the cross section for ZZ plus ZW production, compared to the standard model prediction of 5.0±0.4pb. © 2005 The American Physical Society.

Abstract:

We report a measurement of the tt̄ production cross section using the CDF II detector at the Fermilab Tevatron. The data consist of events with an energetic electron or muon, missing transverse energy, and three or more hadronic jets, at least one of which is identified as a b-quark jet by reconstructing a secondary vertex. The background fraction is determined from a fit of the transverse energy of the leading jet. Using 162 ± 10 pb ^-1 of data, the total cross section is found to be 6.0 ± 1.6(stat.) ± 1.2(syst.) pb, which is consistent with the standard model prediction. © 2005 The American Physical Society.

Abstract:

We present measurements of the lifetimes and polarization amplitudes for B(0)(s)-->J/psiphi and B(0)(d)-->J/psiK(*0) decays. Lifetimes of the heavy and light mass eigenstates in the B(0)(s) system are separately measured for the first time by determining the relative contributions of amplitudes with definite CP as a function of the decay time. Using 203+/-15 B(0)(s) decays we obtain tau(L) = (1.05(+0.16)(-0.13) +/- 0.02) ps and tau(H) = (2.07(+0.58)(-0.46) +/- 0.03) ps. Expressed in terms of the difference DeltaGamma(s) and average Gamma(s), of the decay rates of the two eigenstates, the results are DeltaGamma(s)/Gamma(s) = (65(+25)(-33) +/- 1)% and DeltaGamma(s) = (0.47(+0.19)(-0.24) +/- 0.01) ps(-1).