S. Fajfer, J. Drobnak, J. F. Kamenik
The most general set of new physics effective operators contributing to the
decay of an unpolarized top quark into a bottom quark and a W gauge boson are
considered at next-to-leading order in QCD. We find that the dipole operator
contribution to the transverse-plus W helicity fraction F+ is enhanced compared
to the leading order result at non-vanishing bottom quark mass. Nonetheless,
presently the observable most sensitive to new physics contributions is the
longitudinal W helicity fraction FL. We also investigate constraints on t W b
couplings coming from precision flavor observables, in particular from Delta
B=1 and Delta B=2 transitions of Bq mesons. We find these to be mostly superior
to present direct constraints coming from top decay and single top production
measurements at the LHC and Tevatron.
View original:
http://arxiv.org/abs/1201.6225
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