Professor Daniela Bortoletto

Abstract:

This Letter describes the first determination of bounds on the CP-violation parameter 2βs using Bs0 decays in which the flavor of the bottom meson at production is identified. The result is based on approximately 2000 Bs0→J/ψ decays reconstructed in a 1.35fb-1 data sample collected with the CDF II detector using pp̄ collisions produced at the Fermilab Tevatron. We report confidence regions in the two-dimensional space of 2βs and the decay-width difference ΔΓ. Assuming the standard model predictions of 2βs and ΔΓ, the probability of a deviation as large as the level of the observed data is 15%, corresponding to 1.5 Gaussian standard deviations. © 2008 The American Physical Society.

Abstract:

We present the results of a search for pair production of a new heavy toplike quark t′ decaying to a W boson and another quark using the Collider Detector at FermilabII detector in runII of the Tevatron pp̄ collider. Using a data sample corresponding to 760pb-1 of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed t′ quark mass to a combination of standard model processes and t′ pair production. We see no evidence for t′t̄′ production, and we infer a lower limit of 256GeV/c2 on the mass of the t′ at 95% C.L. assuming standard strong couplings for the t′. © 2008 The American Physical Society.

Abstract:

This paper describes the first measurement of b-quark fragmentation fractions into bottom hadrons in Run II of the Tevatron Collider at Fermilab. The result is based on a 360pb-1 sample of data collected with the CDF II detector in pp̄ collisions at s=1.96TeV. Semileptonic decays of B̄0, B-, and B̄s0 mesons, as well as Λb0 baryons, are reconstructed. For an effective bottom hadron pT threshold of 7GeV/c, the fragmentation fractions are measured to be fu/fd=1.054±0.018(stat)-0.045+0.025(sys)±0. 058(B), fs/(fu+fd)=0.160±0.005(stat)-0.010+0.011(sys)-0.034+0.057(B), and fΛb/(fu+fd)=0.281±0.012(stat)-0.056+0.058(sys)-0.087+0.128(B), where the uncertainty B is due to uncertainties on measured branching ratios. The value of fs/(fu+fd) agrees within one standard deviation with previous CDF measurements and the world average of this quantity, which is dominated by LEP measurements. However, the ratio fΛb/(fu+fd) is approximately twice the value previously measured at LEP. The approximately 2σ discrepancy is examined in terms of kinematic differences between the two production environments. © 2008 The American Physical Society.