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

We study the constraints on possible new physics contributions to the forward-backward asymmetry of muons, AFB(q2), in B→Kμ+μ-. New physics in the form of vector/axial-vector operators does not contribute to AFB(q2), whereas new physics in the form of scalar/pseudoscalar operators can enhance AFB(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.