Nonperturbative m_X cut effects in B -> Xs l+ l- observables

TL;DR

This paper calculates nonperturbative corrections to B -> Xs l+ l- decay observables with hadronic mass cuts, revealing significant subleading effects that impact the extraction of Wilson coefficients and the zero of the forward-backward asymmetry.

Contribution

It provides the first detailed computation of nonperturbative power corrections for all three key observables in B -> Xs l+ l- decay with hadronic mass cuts, including subleading effects.

Findings

Subleading power corrections are about -5% to -10%.

They shift the zero of the forward-backward asymmetry by -0.05 to -0.1 GeV^2.

Corrections are significant for precision tests of new physics.

Abstract

Recently, it was shown that in inclusive B -> Xs l+ l- decay, an angular decomposition provides three independent (q^2 dependent) observables. A strategy was formulated to extract all measurable Wilson coefficients in B -> Xs l+ l- from a few simple integrals of these observables in the low q^2 region. The experimental measurements in the low q^2 region require a cut on the hadronic invariant mass, which introduces a dependence on nonperturbative b quark distribution functions. The associated hadronic uncertainties could potentially limit the sensitivity of these decays to new physics. We compute the nonperturbative corrections to all three observables at leading and subleading order in the power expansion in \Lambda_QCD/m_b. We find that the subleading power corrections give sizeable corrections, of order -5% to -10% depending on the observable and the precise value of the hadronic mass cut. They cause a shift of order -0.05 GeV^2 to -0.1 GeV^2 in the zero of the forward-backward asymmetry.