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

Understand

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.