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Register a new userMeasurement of the fraction of top quark pair events produced via gluon-gluon fusion at the Tevatron in lepton+jets final states
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We report a measurement of the fraction of top quark pair events produced via gluon-gluon fusion in $pbar{p}$ collisions at $sqrt{s} = 1.96 ~rm TeV$ in lepton+jets final states using the full RunII data set corresponding to $9.7 ~rm fb^{-1}$ of integrated luminosity collected by the DO experiment. We utilize a boosted decision tree to distinguish top quark pair events produced by $qbar{q}$ annihilation and $gg$ fusion. We perform a template fit to extract the $tbar{t}$ production fraction via $gg$ fusion and find $f_{gg} = 0.096 pm 0.039 ~(rm stat.) ~^{+0.077}_{-0.062} ~(rm syst.)$.
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We report a measurement of the mass of the top quark in lepton+jets final states of ppbar->ttbar data corresponding to 2.6 fb^{-1} of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. Using a matrix element method, we combine an insitu jet energy calibration with our standard jet energy scale derived in studies of {gamma}+jet and dijet events and employ a novel flavor-dependent jet response correction to measure a top-quark mass of mt = 176.01 +/- 1.64 GeV. Combining this result with our previous result obtained on an independent data set, we measure a top-quark mass of mt = 174.94 +/- 1.49 GeV for a total integrated luminosity of 3.6 fb^{-1}.
The top quark, discovered in 1995 by the CDF and D0 collaborations at the Tevatron proton antiproton collider at Fermilab, has undergone intense studies in the last 20 years. Currently, CDF and D0 converge on their measurements of top-antitop quark production cross sections using the full Tevatron data sample. In these proceedings, the latest results on inclusive and differential measurements of top-antitop quark production cross sections at the Tevatron are reported.
We present the calculation of the cross section and invariant mass distribution for Higgs boson pair production in gluon fusion at next-to-leading order (NLO) in QCD. Top-quark masses are fully taken into account throughout the calculation. The virtual two-loop amplitude has been generated using an extension of the program GoSam supplemented with an interface to Reduze for the integral reduction. The occurring integrals have been calculated numerically using the program SecDec. Our results, including the full top-quark mass dependence for the first time, allow us to assess the validity of various approximations proposed in the literature, which we also recalculate. We find substantial deviations between the NLO result and the different approximations, which emphasizes the importance of including the full top-quark mass dependence at NLO.
Recent developments and results on the comparison of gluon to quark jets are discussed. A most important topic is the introduction of explicit energy scales of the jets. The scaling violation of the fragmentation function and the increase of the multiplicity with scale is shown to be directly proportional to the corresponding gluon or quark colour factor. The ratio of the hadron multiplicity in gluon to quark jets is understood to be smaller than the colour factor ratio due to differences in the fragmentation of the leading quark or gluon. Novel algorithms to reconstruct the colour portraits or the colour flow of an event are presented.
We measure the subjet multiplicity M in jets reconstructed with a successive combination type of jet algorithm (kT). We select jets with 55<pT<100 GeV and |eta|<0.5. We compare similar samples of jets at sqrt(s)=1800 and 630 GeV. The HERWIG Monte Carlo simulation predicts that 59% of the jets are gluon jets at sqrt(s)=1800 GeV, and 33% at sqrt(s)=630 GeV. Using this information, we extract the subjet multiplicity in quark (Mq) and gluon (Mg) jets. We also measure the ratio R= (<Mg> -1)/(<Mq>-1)= 1.84 +- 0.15(stat) +0.22-0.18(sys).
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