Search results for "Bottom"

Search for the supersymmetric partner of the top quark inpp¯collisions ats=1.96  TeV

2010

We present a search for the lightest supersymmetric partner of the top quark in proton-antiproton collisions at a center-of-mass energy root s = 1: 96 TeV. This search was conducted within the framework of the R parity conserving minimal supersymmetric extension of the standard model, assuming the stop decays dominantly to a lepton, a sneutrino, and a bottom quark. We searched for events with two oppositely-charged leptons, at least one jet, and missing transverse energy in a data sample corresponding to an integrated luminosity of 1 fb(-1) collected by the Collider Detector at Fermilab experiment. No significant evidence of a stop quark signal was found. Exclusion limits at 95% confidence …

Search for the lightest scalar top quark in events with two leptons in pp¯ collisions at s=1.96 TeV

2009

Abstract We report results of a search for the pair production of the lightest supersymmetric partner of the top quark, t ˜ 1 , using a data set corresponding to an integrated luminosity of 1 fb −1 collected by the DO detector at a p p ¯ center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. Both scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino. The search is performed in the electron plus muon and dielectron final states. The signal topology consists of two isolated leptons, missing transverse energy, and jets. We find no evidence for this process and exclude regions of parameter space in the framework of the minimal supersymmetric…

Measurement of the top quark pair production cross section in pp collisions at s=7 TeV in dilepton final states with ATLAS

2012

A measurement of the production cross section of top quark pairs (ttbar) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35 pb^-1, a ttbar production cross section of 171 +/- 20(stat.) +/- 14(syst.) +8-6(lum.) pb is measured for an assumed top quark mass of 172.5 GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states ar…

Measurements of spin correlation in top-antitop quark events from proton-proton collisions ats=7  TeVusing the ATLAS detector

2014

Measurements of spin correlation in top quark pair production are presented using data collected with the ATLAS detector at the LHC with proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.6 fb(-1). Events are selected in final states with two charged leptons and at least two jets and in final states with one charged lepton and at least four jets. Four different observables sensitive to different properties of the top quark pair production mechanism are used to extract the correlation between the top and antitop quark spins. Some of these observables are measured for the first time. The measurements are in good agreement with the Stan…

An improved determination of the width of the top quark

2012

We present an improved determination of the total width of the top quark, $\Gamma_t$, using 5.4 fb$^{-1}$ of integrated luminosity collected by the D0 Collaboration at the Tevatron $p\bar{p}$ Collider. The total width $\Gamma_t$ is extracted from the partial decay width $\Gamma(t\to Wb)$ and the branching fraction $\mathcal{B}(t\to Wb)$. $\Gamma(t\to Wb)$ is obtained from the $t$-channel single top quark production cross section and $\mathcal{B}(t\to Wb)$ is measured in $t\bar{t}$ events. For a top mass of $172.5\;\rm GeV$, the resulting width is $\Gamma_t = 2.00^{+0.47}_{-0.43}$ GeV. This translates to a top-quark lifetime of $\tau_t = (3.29^{+0.90}_{-0.63})\times10^{-25}$ s. We also extra…

The two-loop soft function for heavy quark pair production at future linear colliders

2014

We report on the calculation of the threshold soft function for heavy quark pair production in e+ e- annihilation at two-loop order. Our main result is a generalization of the familiar Drell-Yan threshold soft function to the case of non-zero primary quark mass. We set up a framework based on the method of differential equations which allows for the straightforward calculation of the bare soft function to arbitrarily high orders in the dimensional regularization parameter. Remarkably, we find that we can obtain the bare two-loop Drell-Yan soft function from the heavy quark soft function to the order in epsilon required for a two-loop calculation by making simple replacements. We expect that…

Non-perturbatively renormalised light quark masses from a lattice simulation with Nf=2

2006

Abstract We present results for the light quark masses obtained from a lattice QCD simulation with N f = 2 degenerate Wilson dynamical quark flavours. The sea quark masses of our lattice, of spacing a ≃ 0.06 fm , are relatively heavy, i.e., they cover the range corresponding to 0.60 ≲ M P / M V ≲ 0.75 . After implementing the non-perturbative RI-MOM method to renormalise quark masses, we obtain m ud MS ¯ ( 2 GeV ) = 4.3 ± 0.4 −0 +1.1 MeV , and m s MS ¯ ( 2 GeV ) = 101 ± 8 −0 +25 MeV , which are about 15% larger than they would be if renormalised perturbatively. In addition, we show that the above results are compatible with those obtained in a quenched simulation with a similar lattice.

Top quark mass definition andtt¯production near threshold at the Next Linear Collider

2001

We suggest an infrared-insensitive quark mass, defined by subtracting the soft part of the quark self energy from the pole mass. We demonstrate the deep relation of this definition with the static quark-antiquark potential. At leading order in 1/m this mass coincides with the PS mass which is defined in a completely different manner. Going beyond static limit, the small normalization point introduces recoil corrections which are calculated here as well. Using this mass concept and other concepts for the quark mass we calculate the cross section of e+ e- -> t t-bar near threshold at NNLO accuracy adopting three alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS mass, …

Experimental Determination of Weak Quark Mixing Angles in the Eight Quark Scheme

1989

Search for Scalar Bottom Quark Pair Production with the ATLAS Detector inppCollisions ats=7  TeV

2012

The results of a search for pair production of the scalar partners of bottom quarks in 2: 05 fb(-1) of pp collisions at root s = 7 TeV using the ATLAS experiment are reported. Scalar bottom quarks ...