Exclusive semileptonic B → πlvl and Bs → Klvl decays through unitarity and lattice QCD

The Cabibbo-Kobayashi-Maskawa (CKM) matrix element vertical bar V-ub vertical bar is obtained from exclusive semileptonic B -> pi lv(l) and B-s -> Klv(l) decays adopting the unitarity-based dispersion matrix approach for the determination of the hadronic form factors (FFs) in the whole kinematical range. We use lattice computations of the relevant susceptibilities and of the FFs in the large-q(2) regime in order to derive their behavior in the low-q(2) region without assuming any specific momentum dependence and without constraining their shape using experimental data. Then, we address the extraction of vertical bar V-ub vertical bar from the experimental data, obtaining vertical bar V-ub vertical bar = (3.62 +/- 0.47).10(-3) from B -> pi and vertical bar V-ub vertical bar = (3.77 +/- 0.48).10(-3) from B-s -> K, which after averaging yield vertical bar V-ub vertical bar = (3.69 +/- 0.34).10(-3). These results are compatible with the most recent inclusive value |vertical bar V-ub vertical bar(incl) = 4.13 (26).10(-3) at the 1 sigma level. We also present purely theoretical estimates of the ratio of the tau/mu decay rates R-pi(K)(tau/)mu, the normalized forward-backward asymmetry (A) over bar (-l,)(pi)(FB) and the normalized lepton polarization asymmetry (A) over bar (l,)(pi(K))(polar).

Automated summary

This study determines the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V-ub| using a dispersion matrix approach and obtains accurate values through experimental data. The study also provides theoretical estimates for other decay rates and asymmetries.