1,795 research outputs found

    Probing the Anomalous Couplings of the Top Quark with Gluon at the LHC and Tevatron

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    In this paper, we study the sensitivity of the fraction of ttˉt\bar{t} events arising from gluon-gluon fusion to the chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) as well as the total and differential ttˉt\bar{t} cross sections at the LHC and Tevatron. The sensitivity of measured charged asymmetry at the LHC to CEDM and CMDM is also studied. We find that at the Tevatron and the LHC, non-zero values of CMDM could suppress the ttˉt\bar{t} production rate. It is shown that the ratio of σ(gg→ttˉ)/σ(ppˉ→ttˉ)\sigma(gg\rightarrow t\bar{t})/\sigma(p\bar{p}\rightarrow t\bar{t}) at the Tevatron is more sensitive to CEDM and CMDM than the LHC case. The presence of CEDM always increases the contribution of gluon-gluon fusion process in top pair rate at the Tevatron and LHC. Except for a small range of CMDM, the presence of CEDM and CMDM can increase the fraction of gluon-gluon fusion at the Tevatron and LHC. The measured ratio of σ(gg→ttˉ)/σ(ppˉ→ttˉ)\sigma(gg\rightarrow t\bar{t})/\sigma(p\bar{p}\rightarrow t\bar{t}) at the Tevatron is used to derive bounds on the chromoelectric and chromomagnetic dipole moments as well as the total and differential (dσ/dmttˉd\sigma/dm_{t\bar{t}}) cross sections at the LHC and Tevatron, and the measured charged asymmetry at the LHC. The combination of dσTeV/dmttˉd\sigma_{TeV}/dm_{t\bar{t}} and σLHC\sigma_{LHC} provides stringent limits on CMDM and CEDM.Comment: 11 pages,6 figures,2 table

    Secondary particles spectra in the decay of a polarized top quark with anomalous tWbtWb coupling

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    Analytic expression for energy and angular dependence of a secondary charged lepton in the decay of a polarized top quark with anomalous tWbtWb couplings in the presence of all anomalous couplings are derived. The angular distribution of the b-quark is derived as well. It is presented that the charged lepton spin correlation coefficient is not very sensitive to the anomalous couplings. However, the b-quark spin correlation coefficient is sensitive to anomalous couplings and could be used as a powerful tool for searching of non-SM coupling.Comment: 9 pages, 5 figure

    Impact of Torsion Space-Time on ttˉt\bar{t} observables at Hadron Colliders

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    Starting from the effective torsion space-time model, we study its effects on the top pair production cross section at hadron colliders. We also study the effect of this model on top pair asymmetries at the Tevatron and the LHC. We find that torsion space-time can explain forward-backward asymmetry according to measured anomaly at Tevatron. We find an allowed region in the parameters space which can satisfy simultaneously all ttˉt\bar{t} observables measured at Tevatron and LHC.Comment: 17 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1207.064

    Probing the top quark chromoelectric and chromomagnetic dipole moments in single top tWtW-channel at the LHC

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    We study the effects of chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) on the production cross section of single top tWtW-channel at the LHC based on the effective Lagrangian approach. We show that the impact of CEDM and CMDM could be large. Using the experimental measurement of the tWtW-channel cross section, constraints on CEDM and CMDM are extracted. These constraints are comparable with the ones obtained from the top pair analysis.Comment: 13 pages, 4 figure

    Top Quark Asymmetries and Unparticle Physics

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    Among different measured observables of top-antitop quark pairs at hadron colliders, the forward-backward asymmetry (AFBA_{\text{FB}}) measured by the CDF and D0 collaborations has inconsistency with the Standard Model prediction. The measured forward-backward asymmetry grows with ttˉt\bar{t} invariant mass. Several new physics models have been proposed to explain this deviation. We consider the consistency of the parameter space of vector unparticle (in Flavor-Conserving scenario) with the existing ttˉt\bar{t} production measurements. In particular, we look at the total cross sections at the LHC and Tevatron, differential cross section with ttˉt\bar{t} invariant mass, and the LHC charge asymmetry to identify the regions in parameter space that can give the desired top AFBA_{\text{FB}} observed by the Tevatron. We show that in spite of the intrinsic tension between the LHC charge asymmetry and AFBA_{\text{FB}}, there exists a region in the unparticle parameters space where the top AFBA_{\text{FB}} and the LHC charge asymmetry are satisfied simultaneously. Finally, we show that the consistent region with ttˉt\bar{t} observables is consistent with the constraints coming from the dijet resonance searches.Comment: 12 pages,5 figure
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