Large forward-backward asymmetry in B --> K mu+ mu- from new physics tensor operators

TL;DR

This paper investigates how new physics tensor operators can significantly enhance the forward-backward asymmetry in B --> K mu+ mu- decays, potentially reaching up to 40%, and discusses how different operators influence this observable.

Contribution

It demonstrates that tensor operators can cause large A_{FB}(q^2) enhancements, providing a new way to identify tensor contributions in B decays.

Findings

Tensor operators can increase A_{FB}(q^2) up to 40% near high-q^2.

Scalar/pseudoscalar operators only cause minor A_{FB}(q^2) enhancements.

Combined scalar/pseudoscalar and tensor operators can produce A_{FB}(q^2) > 15% across high-q^2 region.

Abstract

We study the constraints on possible new physics contribution to the forward-backward asymmetry of muons, A_{FB}(q^2), in B --> K mu+ mu-. New physics in the form of vector/axial-vector operators does not contribute to A_{FB}(q^2) whereas new physics in the form of scalar/pseudoscalar operators can enhance A_{FB}(q^2) only by a few per cent. However new physics the form of tensor operators can take the peak value of A_{FB}(q^2) to as high as 40% near the high-q^2 end point. In addition, if both scalar/pseudoscalar and tensor operators are present, then A_{FB}(q^2) can be more than 15% for the entire high-q^2 region q^2 > 15 GeV^2. The observation of significant A_{FB} would imply the presence of new physics tensor operators, whereas its q^2 dependence could further indicate the presence of new scalar/pseudoscalar physics.