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تسجيل مستخدم جديدThe Forward-Backward Asymmetry in $Bto D^{*}ell u$: One more hint for Scalar Leptoquarks?
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In recent years, intriguing hints for the violation of lepton flavour universality have accumulated. In particular, deviations from the Standard-Model (SM) predictions in $Bto D^{(*)}tau u/Bto D^{(*)}ell u$, in the anomalous magnetic moment of the muon and {in} $bto sell^+ell^-$ data were observed with a significance of $!>3,sigma$, $>!4,sigma$ and $>!5,sigma$, respectively. Furthermore, in a recent re-analysis of 2018 Belle data, it was found that the forward-backward asymmetry of $bar B to D^{*}mubar u$ vs $bar Bto D^{*}ebar u$ disagrees with the SM prediction by $approx!!4,sigma$ which would be an additional sign of lepton flavour universality violation. Since one naturally expects muon-related new effects to also emerge at some point in $b to cmu u$ decays, the above putative deviation might share a common origin with the other flavour anomalies. We show that a tensor operator is necessary to significantly improve the global fit w.r.t. the SM, which can only be induced (at tree-level in a renormalizable model) by a scalar leptoquark. Interestingly, among the two possible representations, the $SU(2)_L$-singlet $S_1$ and the doublet $S_2$, which can both also account for the anomalous magnetic moment of the muon, only $S_1$ can provide a good fit as it naturally gives rise to the scenario $C_{VL}, C_{SL}=-4 C_T$. While the constraints from (differences of) other angular observables prefer a smaller value $Delta A_{rm FB}$, this scenario is significantly preferred ($approx 3 sigma$) over the SM hypothesis and compatible with constraints such as $Bto K^* u u$ and electroweak precision bounds.
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