Standard Model predictions for B -> Kll with form factors from lattice QCD

TL;DR

This paper provides the first unquenched lattice QCD calculations of form factors for B -> Kll decays, predicting differential branching fractions and angular observables within the Standard Model and comparing with experimental data.

Contribution

It introduces unquenched lattice QCD form factors for B -> Kll decays, enabling precise Standard Model predictions for branching ratios and angular distributions.

Findings

Predicted $ ext{BR}(B o K au au)$ as $(1.44 imes 10^{-7})$

Calculated ratio $R^ au_l$ as 1.159(40)

Compared predictions with experimental measurements

Abstract

We calculate, for the first time using unquenched lattice QCD form factors, the Standard Model differential branching fractions $dB/dq^2(B \to Kll)$ for $l=e, \mu, \tau$ and compare with experimental measurements by Belle, BABAR, CDF, and LHCb. We report on $\mathcal{B}(B \to Kll)$ in $q^2$ bins used by experiment and predict $\mathcal{B}(B \to K \tau \tau) = (1.44 \pm 0.15) 10^{-7}$. We also calculate the ratio of branching fractions $R^\mu_e = 1.00023(63)$ and predict $R^\tau_l = 1.159(40)$, for $l=e, \mu$. Finally, we calculate the "flat term" in the angular distribution of the differential decay rate $F_H^{e, \mu, \tau}$ in experimentally motivated $q^2$ bins.