Abstract
We consider leptonic B^-rightarrow ell ^- {bar{nu }}_ell and semileptonic {bar{B}} rightarrow pi ell ^- {bar{nu }}_ell , {bar{B}} rightarrow rho ell ^- {bar{nu }}_ell decays and present a strategy to determine short-distance coefficients of New-Physics operators and the CKM element |V_{ub}|. As the leptonic channels play a central role, we illustrate this method for (pseudo)-scalar operators which may lift the helicity suppression of the corresponding transition amplitudes arising in the Standard Model. Utilising a new result by the Belle collaboration for the branching ratio of B^-rightarrow mu ^- {bar{nu }}_mu , we explore theoretically clean constraints and correlations between New Physics coefficients for leptonic final states with mu and tau leptons. In order to obtain stronger bounds and to extract |V_{ub}|, we employ semileptonic {bar{B}} rightarrow pi ell ^- {bar{nu }}_ell and {bar{B}} rightarrow rho ell ^- {bar{nu }}_ell decays as an additional ingredient, involving hadronic form factors which are determined through QCD sum rule and lattice calculations. In addition to a detailed analysis of the constraints on the New Physics contributions following from current data, we make predictions for yet unmeasured decay observables, compare them with experimental constraints and discuss the impact of CP-violating phases of the New-Physics coefficients.
Highlights
Leptonic transitions of B mesons are the simplest weak decay class as the final-state particles do not have SU (3)C colour quantum numbers
Decays of B mesons into final states with τ leptons are receiving a lot of interest in view of experimental results which indicate possible signals of New Physics (NP), where the ratios RD(∗) of the branching ratios of B → D(∗)τ −ντ and B → D(∗)μ−νμ decays are in the focus
We continue by adding the observable Rμe,μ ;ρ [q2≤12] GeV2 to the analysis shown in Fig. 5; to incorporate this observable wa|sCtneedμPpas|φs–so|τPuCf.m4τPW5e| ◦eCcoufiePnprss=titodfieCtrxhiμPenφ.gvWμPadleui=feefexφ0rpe◦τPlnoatr=nevdat1hla8uel0elcos◦ow.frToreφrhleτPathtriteeoosnpuschlhtbaianesnetgwgsepeφaeitμPnnterns are shown in Fig. 14, where the overlapping region of the two constraints is indicated in blue
Summary
Leptonic transitions of B mesons are the simplest weak decay class as the final-state particles do not have SU (3)C colour quantum numbers. Decays of B mesons into final states with τ leptons are receiving a lot of interest in view of experimental results which indicate possible signals of New Physics (NP), where the ratios RD(∗) of the branching ratios of B → D(∗)τ −ντ and B → D(∗)μ−νμ decays are in the focus We will obtain constraints on short-distance coefficients using the Belle result in Eq (8) and address the question of how large the branching ratio of B− → e−νe could be due to a lift of the helicity suppression through NP effects. In the leptonic rare Bq0 → + − decays of neutral Bq0 mesons (q = d, s), the impact of Bq0–Bq0 mixing may induce CP-violating asymmetries, thereby indicating possible CP-violating NP phases [22].
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