Probing $B^+ \to K^+$ semi-leptonic FCNC decay with new physics effects under PQCD approach

TL;DR

This paper calculates the $B^+ o K^+$ semi-leptonic FCNC decay rates using PQCD, incorporates new physics via leptoquarks to explain recent experimental anomalies, and refines form factor estimates with lattice QCD data.

Contribution

It provides a NLO PQCD calculation of $B^+ o K^+$ decays, combines lattice QCD data for improved form factors, and introduces leptoquark models to explain experimental anomalies.

Findings

Successful explanation of recent Belle II anomalies with leptoquark models

Improved form factor accuracy through combined PQCD and lattice QCD data

Predicted branching ratios consistent with experimental measurements

Abstract

Recently, the Belle II Collaboration reported the branching fraction $\mathcal{B}(B^+ \to K^+ \nu \bar{\nu})=(2.3\pm0.7)\times10^{-5}$ with a significance of $3.5\sigma$, which is $2.7\sigma$ above the SM expectation. Motivated by this measurement, we calculate this decay channel at the NLO and twist-3 level using the PQCD approach. By combining the lattice QCD data and our results, we obtain form factors with improved accuracy. Using these form factors, we precisely estimate the branching ratios of $B^+ \to K^+$ semileptonic FCNC decays, including $B^+ \to K^+\nu\bar\nu$ and $B^+ \to K^+\ell^+\ell^-$. To explain the anomalies in these two processes, we introduce a leptoquark model as a new physics scenario. Using five possible types of leptoquarks, we successfully explain the latest experimental measurements, and further constraints on the leptoquarks are derived.