Search for scalar top and scalar bottom quarks in pp collisions at square root s=1.8 TeV

We have searched for direct pair production of scalar top and scalar bottom quarks in 88 pb-1 of pp collisions at sqrt[s]=1.8 TeV with the CDF detector. We looked for events with a pair of heavy flavor jets and missing energy, consistent with scalar top (bottom) quark decays to a charm (bottom) quark and a neutralino. The numbers of events that pass our selections show no significant deviation from standard model expectations. We compare our results to the next-to-leading order scalar quark production cross sections to exclude regions in scalar quark-neutralino mass parameter space.     

Search for pair production of scalar bottom quarks in pp collisions at square root of s = 1.96 TeV

A search for direct production of scalar bottom quarks (b) is performed with 310 pb(-1) of data collected by the D0 experiment in pp collisions at square root s = 1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos (chi(1)0), with chi(1)0 assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m(b), m(chi(1)0)) mass plane, improving significantly upon the results from run I of the Tevatron.     

Searching for Higgs decays to four bottom quarks at LHCb

We discuss the feasibility of seeing a Higgs boson which decays to four bottom quarks through a pair of (pseudo-)scalars at the LHCb experiment to argue that the use of b-physics triggers and off-line vertex reconstruction, as opposed to jet triggers with b tagging, may be more effective for this signal. Focusing on inclusive production for the Higgs, we find that for light scalar masses below 20 GeV, signal reconstruction efficiencies of order a few percent may be enough for LHCb to find evidence for a Higgs with a dominant 4b decay channel.     

Search for R-parity violating decays of scalar fermions at LEP

A search for pair produced scalar fermions with couplings that violate R-parity has been performed using a data sample corresponding to an integrated luminosity of 56 pb at a centre-of-mass energy of 183 GeV collected with the OPAL detector at LEP. An important consequence of R-parity breaking interactions is that the lightest supersymmetric particle is expected to be unstable. Searches for R-parity violating decays of charged sleptons, sneutrinos and stop quarks have been performed under the assumptions that the lightest supersymmetric particle decays promptly and that only one of the R-parity violating couplings is dominant for each of the decay modes considered. Such processes would yield multi-leptons, jets plus leptons or multi-jets, with or without missing energy, in the final state. No significant excess of such events has been observed. Limits on the production cross-sections of scalar fermions in R-parity violating scenarios are obtained. Mass exclusion regions are also presented in the framework of the Constrained Minimal Supersymmetric Standard Model. Received: 16 March 1999 / Published online: 14 October 1999     

Search for pair production of scalar top quarks in R-parity violating decay modes in pp collisions at square root of s=1.8 TeV

We present the results of a search for pair production of scalar top quarks (t(1)) in an R-parity violating supersymmetry scenario in 106 pb(-1) of pp collisions at square root of s=1.8 TeV collected by the Collider Detector at Fermilab. In this mode each t(1) decays into a tau lepton and a b quark. We search for events with two tau's, one decaying leptonically (e or mu) and one decaying hadronically, and two jets. No candidate events pass our final selection criteria. We set a 95% confidence level lower limit on the t(1) mass at 122 GeV/c(2) for Br(t(1)-->tau b)=1.     

Single electrons from heavy-flavor decays in collisions at

The invariant differential cross section for inclusive electron production in p+p collisions at [FORMULA: SEE TEXT] has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4相似文献   

Search for scalar top quark production in p&pmacr; collisions at sqrt

We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb(-1) of p&pmacr; collisions at sqrt[s] = 1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c(2) and scalar neutrino masses of at least 40 GeV/c(2), we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios.     

Radial profile of bottom quarks in jets in high-energy nuclear collisions

Angular correlations between a heavy quark(HQ) and its tagged jet are potentially new tools to gain insight into the in-medium partonic interactions in relativistic heavy-ion collisions.In this work,we present the first theoretical study on the radial profiles of B mesons in jets in Pb+Pb collisions at the Large Hadron Collider(LHC).The initial production of a bottom quark tagged jet in p+p is computed by SHERPA,which matches the next-toleading order matrix elements with contributions of parton showers,whereas the massive quark traversing the quarkgluon plasma is described by a Monte Carlo model,SHELL,which can simultaneously simulate light and heavy flavor in-medium energy loss within the framework of Langevin evolution.In p+p collisions,we find that at lower p_T~Q the radial profiles of heavy flavors in jets are sensitive to the heavy quark mass.In 0-10% Pb+Pb collisions at S_(NN)~(1/2)=5.02 TeV,we observe an inverse modification pattern of the B meson radial profiles in jets at 4 p_T~Q 20 GeV compared to those of D mesons:the jet quenching effects narrow the jet radial profiles of B mesons in jets while broadening those of D mesons in jets.We find that in A+A collisions,the contribution dissipated from the higher p_T~Q 20 GeV region naturally has a narrower initial distribution and consequently leads to a narrower modification pattern of the radial profile;however the diffusion nature of the heavy flavor in-medium interactions will give rise to a broader modification pattern of the radial profile.These two effects consequently compete and offset with each other,and the b quarks in jets benefit more from the former and suffer less diffusion effect compared to that of c quarks in jets.These findings can be tested in the future experimental measurements at the LHC to gain better understanding of the mass effect of jet quenching.     

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^?1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.     

Search for flavor changing neutral currents in top quark decays in pp collisions at 7 TeV

The results of a search for flavor changing neutral currents in top quark decays $\mathrm{t}\to \mathrm{Zq}$ in events with a topology compatible with the decay chain $\mathrm{t}\overline{\mathrm{t}}\to \mathrm{Wb}+\mathrm{Zq}\to ?\nu \mathrm{b}+??\mathrm{q}$ are presented. The search is performed with a data sample corresponding to an integrated luminosity of $5.0{\text{fb}}^{?1}$ of proton–proton collisions at a center-of-mass energy of 7 TeV, collected with the CMS detector at the LHC. The observed number of events agrees with the standard model prediction and no evidence for flavor changing neutral currents in top quark decays is found. A $\mathrm{t}\to \mathrm{Zq}$ branching fraction greater than 0.21% is excluded at the 95% confidence level.     

Search for charged Higgs bosons from top quark decays in pp collisions at square root s=1.96 TeV

We report the results of a search for a charged Higgs boson in the decays of top quarks produced in pp collisions at a center-of-mass energy of 1.96 TeV. We use a data sample corresponding to an integrated luminosity of 193 pb-1 collected by the upgraded Collider Detector at Fermilab. No evidence for charged Higgs production is found, allowing 95% C.L. upper limits to be placed on BR(t-->H+b) for different charged Higgs decay scenarios. In addition, we present in the minimal supersymmetric standard model (mH+/-, tanbeta) plane the first exclusion regions with radiative and Yukawa coupling corrections.     

Search for pair production of scalar top quarks decaying to a tau lepton and a b quark in pp over collisions at sqrt s=1.96 TeV

We search for pair production of supersymmetric top quarks (t over1), followed by R-parity violating decay t over1-->taub with a branching ratio beta, using 322 pb(-1) of pp over collisions at sqrt s=1.96 TeV collected by the upgraded Collider Detector at Fermilab. Two candidate events pass our final selection criteria, consistent with the standard model expectation. We set upper limits on the cross section sigma(t over1t over1) x beta2 as a function of the top-squark mass m(t over1). Assuming beta=1, we set a 95% confidence level limit m(t over1)>153 GeV/c2. The limits are also applicable to the case of a third-generation scalar leptoquark (LQ3) decaying LQ3-->taub.