Long-Distance Dominance of the CP Asymmetry in B->X_{s,d}+gamma Decays

TL;DR

This paper analyzes the dominant long-distance contribution to the CP asymmetry in B->X_{s,d}+gamma decays within the Standard Model, highlighting its dependence on a single hadronic parameter and implications for new physics detection.

Contribution

It identifies the leading long-distance effect in CP asymmetry as arising from a specific interference process and relates it to a non-local hadronic parameter, providing a basis for future experimental tests.

Findings

Long-distance effects dominate the CP asymmetry in B->X_{s,d}+gamma decays.

The asymmetry depends on a single hadronic parameter Lambda_{17}^u.

Future measurements can signal new physics if asymmetry is below -2%.

Abstract

We show that in the Standard Model the parametrically leading (by a factor 1/alpha_s) contribution to the inclusive CP asymmetry in B->X_{s,d}+gamma decays arises from a long-distance effect in the interference of the electromagnetic dipole amplitude with the amplitude for an up-quark penguin transition accompanied by soft gluon emission. This contribution is governed by a single hadronic parameter Lambda_{17}^u related to a matrix elements of a non-local operator. In view of current experimental data, a future precision measurement of the flavor-averaged CP asymmetry in B->X_s+gamma will signal the presence of new physics only if a value below -2% is found. A cleaner probe of new physics is offered by the difference of the CP asymmetries in charged versus neutral B-meson decays.