Impact of $B\to K^\ast_0 \ell^+\ell^-$ on the New Physics search in $B\to K^\ast \ell^+\ell^-$ decay

TL;DR

This paper examines how unwanted $B o K_0^ ext{*} o K ext{pi}\, ext{leptons}$ events affect the measurements of $B o K^ ext{*} ext{pi} ext{leptons}$ decays, highlighting potential uncertainties in angular distributions and asymmetries.

Contribution

It identifies the impact of scalar $K_0^ ext{*}$ contamination on the precision of $B o K^ ext{*} ext{pi} ext{leptons}$ decay analyses, especially in the low $q^2$ region.

Findings

Unwanted $B o K_0^ ext{*} ext{pi} ext{leptons}$ events can increase decay rate measurements by up to 10% at low $q^2$.

These events can cause sizable uncertainties in transverse asymmetries around $q^2=2$ GeV$^2$.

The impact on other $q^2$ values is estimated to be under 10%.

Abstract

We discuss the uncertainty related to the amount of unwanted $B\to K_0^\ast (K\pi)\ell^+\ell^-$ events in the sample of $B\to K^\ast (K\pi)\ell^+\ell^-$. Those events can increase the measured differential decay rate by up to 10% in the low $q^2$ region, and can be a source of non-negligible uncertainty in the full angular distribution of the $B\to K^\ast (K\pi)\ell^+\ell^-$ decay. Although the transverse asymmetries should be unaffected by the presence of the $S$-wave $K\pi$ pairs, coming from the scalar $K_0^\ast$ meson, we show that in practice their normalization might be sensitive to those events and could entail a sizable uncertainty in transverse asymmetries around $q^2=2 GeV^2$. For other $q^2$'s that error is under about 10%.