Angular Distributions of B -> K ll Decays

TL;DR

This paper provides a model-independent analysis of B -> K ll decay angular distributions, predicting Standard Model values and exploring potential signals of new physics through various observables and decay rate ratios.

Contribution

It introduces a comprehensive framework for analyzing B -> K ll decays, including new observables and precise Standard Model predictions, facilitating new physics searches.

Findings

F_H^l is approximately 2% with small uncertainty in the Standard Model.

R_K is predicted to be one with negligible lepton mass corrections.

Significant room exists for new physics signals in angular observables and decay ratios.

Abstract

We model-independently analyze the angular distributions of B -> K ll decays, l = e, mu, for low dilepton mass using QCD factorization. Besides the decay rate, we study the forward-backward asymmetry A_FB^l and a further observable, F_H^l, which gives rise to a flat term in the angular distribution. We find that in the Standard Model F_H^l ~ m_l^2, hence vanishing F_H^e and F_H^mu of around 2% (exact value depends on cuts) with a very small theoretical uncertainty of a few percent. We also give predictions for R_K, the ratio of B -> K mu mu to B -> K ee decay rates. We analytically show using large recoil symmetry relations that in the Standard Model R_K equals one up to lepton mass corrections of the order 10^(-4). The New Physics reach of the observables from the B -> K ll angular analysis is explored together with R_K and the B_s -> ll and B -> X_s ll branching ratios for both l = e and l = mu. We find substantial room for signals from (pseudo-) scalar and tensor interactions beyond the Standard Model. Experimental investigations of the B -> K mu mu angular distributions are suitable for the LHC environment and high luminosity B factories, where also studies of the electron modes are promising.