Measurement of the fraction of t(t)over-bar production via gluon-gluon fusion in p(p)over-bar collisions at root s=1.96 Tev (original) (raw)
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2009
We present a measurement of the ratio of the tt production cross section via gluon-gluon fusion to the total tt production cross section in pp collisions at ffiffiffi sp ¼ 1: 96 TeV at the Tevatron. Using a data sample with an integrated luminosity of 955 pb À1 recorded by the CDF II detector at Fermilab, we select events based on the tt decay to lepton þ jets. Using an artificial neural network technique we discriminate between tt events produced via qq annihilation and gg fusion, and find Gf ¼ ðgg! t tÞ= ðp p!
Measurement of the t t ¯ production cross section using dilepton events in p p ¯ collisions
Physics Letters B, 2011
We present a measurement of the top quark pair production cross section in pp collisions at √ s = 1.96 TeV using approximately 1 fb −1 collected with the DØ detector. We consider decay channels containing two high p T charged leptons where one lepton is identified as an electron or a muon while the other lepton can be an electron, a muon or a hadronically decaying τ lepton. For a mass of the top quark of 170 GeV, the measured cross section is 7.5 +1.0 −1.0 (stat) +0.7 −0.6 (syst) +0.6 −0.5 (lumi) pb. Using τ events only, we measure: σ tt × B(tt → τ bb) = 0.13 +0.09 −0.08 (stat) +0.06 −0.06 (syst) +0.02 −0.02 (lumi) pb. Comparing the measured cross section as a function of the mass of the top quark with a partial next-to-next-to leading order Quantum Chromodynamics theoretical prediction, we extract a mass of the top quark of 171.5 +9.9 −8.8 GeV, in agreement with direct measurements. 180 DØ Collaboration / Physics Letters B 679 (2009) 177-185 14.60.Fg 12.15.Ff The top quark, first observed at Fermilab in 1995 , is the heaviest known elementary particle. In many extensions of the standard model (SM) new physics is predicted in connection with top quarks. In the SM, top quarks are predicted to decay into a W boson and a b quark with a branching fraction of nearly 100% . For approximately 10% of all top-antitop quark (tt) events, both W bosons decay leptonically and generate final states containing two leptons . In addition, these final states are characterized by the presence of two high energy jets resulting from hadronization of the two b quarks and large imbalance in transverse momentum (/ E T ) due to several undetected neutrinos from the W boson decays.
2006
At the Tevatron, the dominant standard model mechanism for top quark production in pp collisions is predicted to be qq annihilation to t t. The top quark decays immediately into a W boson and ab quark almost 100% of the time. The W boson subsequently decays to either a pair of quarks or a lepton-neutrino pair. The measurement of the tt cross section tests the QCD calculations for the pair production of a massive color triplet. These calculations have been performed in perturbation theory at the next-toleading order [1].
On Gluon Radiation in $ t\ bar t $ Production and Decay
Understanding the pattern of gluon radiation in tt production processes is important for making an accurate determination of the top mass from the measurement of its decay products. In a recent paper we showed that the exact matrix element and parton shower (HERWIG) calculations gave very different results for the distribution of gluon jets in tt production at the Tevatron pp collider. By repeating the calculation for the simpler e + e − → bbW + W − g process, we reveal even more dramatic differences between the two approaches. We conclude that there are significant differences in gluon radiation between HERWIG and the matrix element calculation in regions of phase space where one would expect agreement.