A large forward-backward asymmetry is seen in both the top-quark rapidity distribution (AFB_t) and the rapidity distribution of charged leptons (AFB_l) from top quarks produced at the Tevatron. The observed asymmetry deviates by about 3 standard deviations from standard model of particle physics expectations. The deviation motives theorists build up many models of new physics beyond the standard model, e.g. the axigluon model, flavor changing neutral current model, flavor changing charged current models, etc.

Dr. Qing-Hong Cao and his collaborators studied the kinematic and dynamics aspects of the relationship of the two asymmetries (AFB_t and AFB_l) based on the spin correlation between charged leptons and the top quark with different polarization states. In the letter Dr. Cao et al concluded that a new physics model which produces more right-handed than left-handed top quarks is favored by the present data. The work is published rapidly in the journal of Physical Review Letter [PRL 108, 072002 (2012)].