Searching for New Physics with Top Quark Decays

Friday December 3rd, 14:15hs - Seminar room

Speaker: Jernej F. Kamenik (Jozef Stefan Institute, Ljubljan)



We analyze possible new physics signals in the decays of the top quark within an effective field theory approach. In particular, we compute the branching ratios for the rare top quark decays t to c gamma and t to c Z mediated by effective flavor changing neutral couplings at the next-to-leading order in QCD including the effects due to operator mixing.

We find that the t to c gamma decay can be used to probe also the effective operators mediating t to c gluon processes. Furthermore we identify angular asymmetries in rare three-body top quark decays able to disentangle the underlying new physics operator contributions. We also consider the impact of non-standard tbW effective operators in the decay t to b W at next- to-leading order in QCD. We find that the dipole operator O_{LR} contribution to the transverse-plus W helicity fraction F_+ is significantly enhanced compared to the leading order result. Nonetheless, presently the most sensitive observable to direct O_{LR} contributions is the longitudinal W helicity fraction F_L. In particular, the most recent CDF measurement of F_L already provides the most stringent upper bound on O_{LR} contributions, even when compared with indirect bounds from the rare decay B to



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