Large forward-backward asymmetry in B→Kμ⁺μ⁻ from new physics tensor operators

Abstract

We study the constraints on possible new physics contributions to the forward-backward asymmetry of muons, A_FB(q²), in B→Kμ⁺μ⁻. New physics in the form of vector/axial-vector operators does not contribute to A_FB(q²), whereas new physics in the form of scalar/pseudoscalar operators can enhance , A_FB(q²) only by a few percent. However, new physics in the form of tensor operators can take the peak value of AFB(q²) to as high as 40% near the high-q² end point. In addition, if both scalar/pseudoscalar and tensor operators are present, then AFB(q²) can be more than 15% for the entire high- q² region q²>15  GeV². The observation of significant AFB would imply the presence of new physics tensor operators, whereas its q² dependence could further indicate the presence of new scalar/pseudoscalar physics.