Abstract
Abstract At the LHC, top quark pairs are dominantly produced from gluons, making it difficult to measure the top quark forward-backward asymmetry. To improve the asymmetry measurement, we study variables that can distinguish between top quarks produced from gluons and those from quarks: the invariant mass of the top pair, the rapity of the top-antitop system in the lab frame, the rapity of the top quark in the top quark polarization and the top-antitop spin correlation. We combine all the variables in a likelihood discriminant method to separate gluon-initiated events from quark-initiated events. We apply our method on models including G-prime’s and W-prime’s motivated by the recent observation of a large top quark forward-backward asymmetry at the Tevatron. We have found that the significance of the asymmetry measurement can be enhanced by 10% to 30%. At the same time, the central values of the asymmetry increase by 40% to 100%. We have also obtained the best spin quantization axes for studying top quark polarization as well as spin-correlation for the new physics models.
Highlights
Models, we see that the measurement of AFB at the LHC will be diluted by this additional SM background
To improve the asymmetry measurement, we study variables that can distinguish between top quarks produced from gluons and those from quarks: the invariant mass of the top pair, the rapity of the top-antitop system in the lab frame, the rapity of the top quark in the top quark polarization and the top-antitop spin correlation
For all new physics explanations of AFB, the differential cross sections in Mtthave been predicted to be different from the SM
Summary
To explain the large top quark forward-backward asymmetry measured at the Tevatron, there are two basic top quark pair production mechanisms. Model C: the contact interaction obtained by integrating out a very heavy axigluon (above the center of mass energy of the LHC and the Tevatron), ξ uγμγ5tau tγμγ5tat/Λ2, with gVq,t = 0, ξ = −1 and Λ ≡ MG′ /(gAq gAt )1/2 = 650 GeV. From the Parton Distribution Functions (PDF’s), one expects |ytt| from uuproductions to be statistically larger than from gg This is the case as shown in the right panel of figure 1, from which one can see that Model A and Model C have more signal events at larger values of |ytt|. We consider the rapidity of the top quark in the ttcenter-of-mass frame: |yt| This variable is especially useful for selecting signal events for Model B. This is because of the t-channel differential cross section enhancement in the forward direction. The rapidity distributions of top quark in the center-of-mass frame of the ttsystem
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
