Precision studies of top quark properties are currently underway at the LHC and Tevatron colliders with the prospect of probing anomalous t−W −b interactions. In the mean time, recent experimental results for the B d,s −B d,s oscillation observables, the branching ratio Bs → µ + µ − , as well as the forward -backward asymmetry in B → K * + − , accompanied by the accurate theoretical predictions for the relevant observables obtained within the SM motivate a combined study of these observables in the presence of anomalous t − W − b vertices. We investigate contributions of such anomalous couplings to the B → Xs + − decay mode, and combining them with the modifications of the B d,s −B d,s , B → Xsγ observables, we determine indirect bounds on the real and imaginary parts of the anomalous t − W − b interactions. We find these to be mostly superior to present direct constraints coming from top decay and production measurements at the LHC and Tevatron.
We show that the charge asymmetry in tt production at the LHC, AC , and the forward-backward asymmetry at the Tevatron, AF B , are in general not tightly correlated. They can even have opposite signs, if the underlying new physics (NP) model is general enough. We demonstrate this using two examples of NP: a light axigluon, and a vector that is a color octet and electroweak triplet. The small value of AC measured at the LHC is thus shown not to exclude a NP interpretation of the anomalously large AF B at the Tevatron. We identify two observables where significant NP effects are still expected at the Tevatron and the LHC, the bb production forward-backward asymmetry and spin polarizations of the pair-produced tops and anti-tops. Introduction.The forward-backward asymmetry (FBA) in tt production at the Tevatron has been measured by both the CDF [1, 2] and DØ [3] collaborations and found to be significantly larger than the standard model (SM) predictions. The naïve average of the inclusive FBA, adding the uncertainties in quadrature, is
A colored weak singlet scalar state with hypercharge 4/3 is one of the possible candidates for the explanation of the unexpectedly large forward-backward asymmetry in t tbar production as measured by the CDF and D0 experiments. We investigate the role of this state in a plethora of flavor changing neutral current processes and precision observables of down-quarks and charged leptons. Our analysis includes tree- and loop-level mediated observables in the K and B systems, the charged lepton sector, as well as the Z to b bbar decay width. We perform a global fit of the relevant scalar couplings. This approach can explain the (g-2)_mu anomaly while tensions among the CP violating observables in the quark sector, most notably the nonstandard CP phase (and width difference) in the Bs system cannot be fully relaxed. The results are interpreted in a class of grand unified models which allow for a light colored scalar with a mass below 1TeV. We find that the renormalizable SU(5) scenario is not compatible with our global fit, while in the SO(10) case the viability requires the presence of both the 126- and 120-dimensional representations.Comment: 26 pages, 7 figures; version as publishe
We consider contributions of non-standard tbW effective operators to the decay of an unpolarized top quark into a bottom quark and a W gauge boson at next-to-leading order in QCD. We find that OLR ≡bLσµν tRW µν contribution to the transverse-plus W helicity fraction (F+) is significantly enhanced compared to the leading order result at non-vanishing bottom quark mass. Nonetheless, presently the most sensitive observable to direct OLR contributions is the longitudinal W helicity fraction FL. In particular, the most recent CDF measurement of FL already provides the most stringent upper bound on OLR contributions, even when compared with indirect bounds from the rare decay B → Xsγ.
We compute the branching ratios for the rare top quark decays t→cγ and t→cZ mediated by effective flavor changing neutral couplings at next-to-leading order in QCD, including the effects due to operator mixing. After resumming contributions of the order of [α{s}log(Λ/m{t})]{n}, where Λ is the scale at which the effective operators are generated, using renormalization group methods, we compute finite matrix element corrections and study the effects of experimental kinematic cuts on the extracted branching ratios. We find that the t→cγ decay can also be used to probe the effective operators mediating t→cg processes, since the latter can naturally contribute 10% or more to the radiative decay. Conversely, any experimental signal of t→cg would indicate a natural lower bound on t→cZ, γ.
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