$B\to K \eta^{(\prime)} \gamma$ decays in the standard model and in scenarios with universal extra dimensions

TL;DR

This paper analyzes $B o K \, \eta^{(\prime)} \gamma$ decays within the Standard Model and models with universal extra dimensions, highlighting their role in CP violation and potential new physics effects, supported by form factor calculations.

Contribution

It provides a detailed theoretical analysis of radiative $B$ decays, including form factor computation and exploration of extra-dimensional new physics scenarios.

Findings

Reproduces the observed decay hierarchy between $\eta$ and $\eta'$ modes.

Calculates the $B^* \to K$ form factor using light cone QCD sum rules.

Shows sensitivity of $B \to K \eta \gamma$ decays to universal extra dimensions.

Abstract

We study the radiative $B \to K \eta^{(\prime)} \gamma$ decays, which are important to investigate CP violation, and are also relevant to assess the role of the exclusive modes induced by the $b \to s \gamma$ transition to saturate the inclusive $B \to X_s \gamma$ decay rate. Moreover, these channels do not display the same hierarchy as $B \to K \eta^{(\prime)}$ modes, for which the decay into $\eta^\prime$ is enhanced with respect to one into $\eta$. The three-body radiative decays reverse the role: we find that this experimentally observed behavior (although affected by a large uncertainty in the case of the $\eta^\prime$) is reproduced in the theoretical analysis. We compute a $B^* \to K$ form factor, needed for this study, using light cone QCD sum rules, and discuss a relation expected to hold in the large energy limit for the light meson. Finally, we examine $B\to K \eta \gamma$ in two extensions of the standard model with universal extra dimensions, to investigate the sensitivity of this rare mode to such a kind of new physics effects.