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 360 pb-1 sample of data collected with the CDF II detector in p-pbar collisions at sqrt{s}=1.96 TeV. Semileptonic decays of B0, B+, and B_s mesons, as well as Lambda_b baryons, are reconstructed. For an effective bottom hadron p_T threshold of 7 GeV/c, the fragmentation fractions are measured to be f_u/f_d=1.054 +/- 0.018 (stat) +0.025-0.045(sys) +/- 0.058 (Br), f_s/(f_u+f_d)=0.160 +/- 0.005 (stat) +0.011-0.010 (sys) +0.057-0.034 (Br), and f_{Lambda_b}/(f_u+f_d)=0.281\pm0.012 (stat) +0.058-0.056 (sys) +0.128-0.086 (Br), where the uncertainty (Br) is due to uncertainties on measured branching ratios. The value of f_s/(f_u+f_d) 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 f_{Lambda_b}/(f_u+f_d) is approximately twice the value previously measured at LEP. The approximately 2 sigma discrepancy is examined in terms of kinematic differences between the two production environments.
Top-quark physics is one of the main fields of investigation at the Tevatron accelerator and, ultimately, at the LHC. We perform a phenomenological analysis of ttbar events at hadron colliders, with a focus on observables relying on bottom-quark fragmentation in top-quark decay. In particular, we investigate the B-lepton invariant-mass distribution in the dilepton channel and give an estimate of the contribution of bottom fragmentation to the Monte Carlo uncertainty on the top-quark mass reconstruction.
We study the scaled-energy (x_B) distribution of bottom-flavored hadrons (B) inclusively produced in top-quark decays at next-to-leading order (NLO) in the general-mass variable-flavor-number scheme endowed with realistic, nonperturbative fragmentation functions that are obtained through a global fit to e^+e^- data from CERN LEP1 and SLAC SLC exploiting their universality and scaling violations. Specifically, we study the effects of gluon fragmentation and finite bottom-quark and B-hadron masses. We find the NLO corrections to be significant. Gluon fragmentation leads to an appreciable reducti…
We report on a search for the supersymmetric partner of the bottom quark produced from gluino decays in data from 2.5 fb-1 of integrated luminosity collected by the Collider Detector at Fermilab at sqrt(s)=1.96 TeV. Candidate events are selected requiring two or more jets and large missing transverse energy. At least two of the jets are required to be tagged as originating from a b quark to enhance the sensitivity. The results are in good agreement with the prediction of the standard model processes, giving no evidence for gluino decay to sbottom quarks. This result constrains the gluino-pair-…
The QCD phenomenology of prompt photon production from e-p to p-p/p-pbar and A-A collisions is reviewed. The use of prompt photons as a probe of (i) parton distribution functions (in a proton or in nuclei) as well as (ii) fragmentation functions (into photons and hadrons) and their medium-modifications is highlighted.
We study the inclusive production of bottom-flavored hadrons from semileptonic decays of polarized top quarks at next-to-leading order in QCD using fragmentation functions recently determined from a global fit to $e^+e^-$ data. We provide the relevant differential decay widths at parton level in analytic form. These results fill an important gap in the theoretical interpretation of recent measurements of the top-quark polarization and the $t\bar{t}$ spin correlations using dilepton final states in proton-proton collisions at the CERN Large Hadron Collider. As an illustration, we study the dist…
We present properties of weakly decaying bottom baryons, Xi_b and Omega_b, using 4.2 fb^-1 of data from p-pbar collisions at sqrt{s}=1.96 TeV, and recorded with the Collider Detector at Fermilab. We report the observation of the Omega_b through the decay chain Omega_b -> J/psi Omega^-, where J/psi -> mu^+ mu^-, Omega^- -> Lambda K^-, and Lambda -> p pi^-. Significance of the observed signal is estimated to be 5.5 Gaussian standard deviations. The Omega_b mass and lifetime are measured to be 6054.4 +- 6.8 (stat.) +- 0.9 (syst.) MeV/c^2 and 1.13^{+0.53}_{-0.40}(stat.) +- 0.02(syst.) ps, respecti…
Using their full Tevatron Run II data sets, the CDF and D0 Experiments present measurements of CP-violating asymmetries in the charmless decay of bottom baryons Lambda-b => p pi-, Lambda-b => p K-, and also for Bs0 => K- pi+, B0 => K+ pi-, Ds => phi pi, and for single muons and like-sign dimuons in p-pbar collisions. Except for the like-sign dimuon asymmetry, these asymmetry measurements are consistent with available predictions of the standard model.
Heavy flavor productions are important tests of QCD. In proton-proton collisions collected at LHCb, a long list of measurements for charm and bottom productions have been made. This talk focuses on the studies of fragmentation functions and production asymmetries for bottom hadrons. They provide inputs for absolute branching fraction measurements and CP violation studies at LHCb respectively.
We present a measurement of the top-quark pair production cross-section in proton-antiproton collisions at $\sqrt{s}$=1.96 TeV. The data were collected at the Fermilab Tevatron by the CDF II detector and correspond to an integrated luminosity of 8.8 fb$^{-1}$, representing the complete CDF Run II data set. We select events consistent with the production of top-quark pairs by requiring the presence of two reconstructed leptons, an imbalance in the total event transverse momentum, and jets. At least one jet is required to be identified as consistent with the fragmentation of a bottom quark using…
The single inclusive spectrum of charged particles with transverse momenta pT=3-150 GeV/c measured at midrapidity by the CDF experiment in proton-antiproton (p-pbar) collisions at sqrt(s)=1.96 TeV is compared to next-to-leading order (NLO) perturbative QCD calculations using the most recent parametrizations of the parton distributions and parton-to-hadron fragmentation functions. Above pT~20 GeV/c, there is a very sizeable disagreement of the Tevatron data compared to the NLO predictions and to xT-scaling expectations, suggesting a problem in the experimental data. We also present the predicti…
We study the inclusive production of J/psi and psi(2S) mesons originating from the decays of bottom-flavored hadrons produced in p anti-p collisions at the Fermilab Tevatron and in pp collisions at the CERN LHC. We work at next-to-leading order in the general-mass variable-flavor-number scheme (GM-VFNS) implemented with nonperturbative fragmentation functions fitted to e^+e^- data of inclusive b-hadron production exploiting their universality. The three-momentum distributions of the charmonia used were extracted from B-decay data in the framework of nonrelativistic-QCD factorization. Comparing…
This paper reports the results of a search for strong production of supersymmetric particles in 20.1 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of 8 TeV using the ATLAS detector at the LHC. The search is performed separately in events with either zero or at least one high $p_\mathrm{T}$ lepton (electron or muon), large missing transverse momentum, high jet multiplicity and at least three jets identified as originated from the fragmentation of a b-quark. No excess is observed with respect to the Standard Model predictions. The results are interpreted in the context of seve…
