Revisiting the one leptoquark solution to the R(D(∗)) anomalies and its phenomenological implications

By Xin-Qiang Li, Ya-Dong Yang, Xin Zhang. 2016

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A bstractIt has been shown recently that the anomalies observed in B¯→D*τν¯τ$$ \overline{B}\to {D}^{\left(*\right)}\tau {\overline{\nu}}_{\tau } $$ and B¯→K¯ℓ+ℓ−$$ \overline{B}\to \overline{K}{\ell}^{+}{\ell}^{-} $$ decays could be resolved with just one scalar leptoquark. Fitting to the current data on R(D(∗)) along with acceptable q2 distributions in B¯→D∗τν¯τ$$ \overline{B}\to {D}^{\left(\ast \right)}\tau {\overline{\nu}}_{\tau } $$ decays, four best-fit solutions for the operator coefficients have been found. In this paper, we explore the possibilities of how to discriminate these four solutions. Firstly, we find that two of them are already excluded by the decay Bc−→τ−ν¯τ$$ {B}_c^{-}\to {\tau}^{-}{\overline{\nu}}_{\tau } $$, because the predicted decay widths have already overshot the total width ΓBc . It is then found that the remaining two solutions result in two effective Hamiltonians governing b→cτν¯τ$$ b\to c\tau {\overline{\nu}}_{\tau } $$ transition, which differ by a sign and enhance the absolute value of the coefficient of c¯LγμbLτ¯LγμντL$$ {\overline{c}}_L{\gamma}_{\mu }{b}_L{\overline{\tau}}_L{\gamma}^{\mu }{\nu}_{\tau\ L} $$ operator by about 12%. However, they give nearly the same predictions as in the SM for the D∗ and τ longitudinal polarizations as well as the lepton forward-backward asymmetries in B¯→D∗τν¯τ$$ \overline{B}\to {D}^{\left(\ast \right)}\tau {\overline{\nu}}_{\tau } $$ decays. For the other observables like ℬBc−→τ−ν¯τ,ℬBc−→γτ−ν¯τ,RD∗q2,dℬB¯→D∗τν¯τ/dq2$$ \mathrm{\mathcal{B}}\left({B}_c^{-}\to {\tau}^{-}{\overline{\nu}}_{\tau}\right),\mathrm{\mathcal{B}}\left({B}_c^{-}\to \gamma {\tau}^{-}{\overline{\nu}}_{\tau}\right),{R}_{D\left(\ast \right)}\left({q}^2\right),\ \mathrm{d}\mathrm{\mathcal{B}}\left(\overline{B}\to {D}^{\left(\ast \right)}\tau {\overline{\nu}}_{\tau}\right)/\mathrm{d}{q}^2 $$ and ℬBc−→X3τν¯τ$$ \mathrm{\mathcal{B}}\left({B}_c^{-}\to {X}_3\tau {\overline{\nu}}_{\tau}\right) $$, on the other hand, the two solutions give sizable enhancements relative to the SM predictions. With measurement of Bc−→τ−ν¯τ$$ {B}_c^{-}\to {\tau}^{-}{\overline{\nu}}_{\tau } $$ at LHCb and refined measurements of observables in B¯→D∗τν¯τ$$ \overline{B}\to {D}^{\left(\ast \right)}\tau {\overline{\nu}}_{\tau } $$ at both LHCb and Belle-II, such a specific NP scenario could be further deciphered.

Subfields: Artificial Intelligence, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/adb03d33635b9d2f2475ea7d43bd70af8a566b22

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