Professor Daniela Bortoletto

Abstract:

We report on a study of diffractive dijet production in p̄p collisions at √s=1.96TeV using the CDF II detector at the Fermilab Tevatron p̄p collider. A data sample from 310pb -1 of integrated luminosity collected by triggering on a high transverse energy jet, ETjet, in coincidence with a recoil antiproton detected in a Roman pot spectrometer is used to measure the ratio of single-diffractive to inclusive-dijet event rates as a function of xp ̄ of the interacting parton in the antiproton, the Bjorken-x, xBjp̄, and a Q2(ETjet)2 in the ranges 10 -3-4GeV2. The t p̄ dependence is measured as a function of Q2 and xBjp̄ and compared with that of inclusive single diffraction dissociation. We find weak xBjp̄ and Q2 dependencies in the ratio of single diffractive to inclusive event rates, and no significant Q2 dependence in the diffractive t p̄ distributions. © 2012 American Physical Society.

Abstract:

The Λb differential production cross section and the cross section ratio σ(Λ-b)/σ(Λb) are measured as functions of transverse momentum pTΛb and rapidity |yΛb| in pp collisions at s=7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on Λb decays reconstructed in the exclusive final state J/ψΛ, with the subsequent decays J/ψ→μ+μ- and Λ→pπ, using a data sample corresponding to an integrated luminosity of 1.9 fb-1. The product σ(Λb)×B(Λb→J/ψΛ) versus pTΛb falls faster than that of b mesons. The measured value of σ(Λb)×B(Λb→J/ψΛ) for pTΛb>10 GeV and |yΛb|<2.0 is 1.16±0.06±0.12nb, and the integrated σ(Λ-b)/σ(Λb) ratio is 1.02±0.07±0.09, where the uncertainties are statistical and systematic, respectively. © 2012 CERN.

Abstract:

A search for narrow, high-mass resonances decaying to electron or muon pairs has been performed using pp collision data collected at s=7TeV by the CMS experiment in 2011. The data sample corresponds to an integrated luminosity of approximately 5 fb -1. The event yields observed in the signal regions are consistent with predictions of the standard model backgrounds, and upper limits on the cross section times branching fraction for a resonance decaying to dileptons are extracted from a shape analysis of the dilepton invariant mass distribution. The resulting mass limits at 95% confidence level are 2330 GeV for the Z ' in the Sequential Standard Model, 2000 GeV for the superstring-inspired Z ψ' resonance, 890 (540) GeV for the Stueckelberg extension Z St' with the mass parameter ε=0.06 (0.04), and 2140 (1810) GeV for Kaluza-Klein gravitons with the coupling parameter k/M- Pl of 0.10 (0.05). These limits are the most stringent to date. © 2012 Elsevier B.V.