Two-photon contribution to polarization in K+--> pi + micro+ micro-

Short-distance physics involving virtual top and charm quarks contributes to μ + (and μ − ) polarization in the decay K + →π + m + m − . Measurement of the parity-violating asymmetry (Γ R −Γ L )/(Γ R +Γ L ), where Γ R and Γ L are the rates to produce right- and left-handed μ + , may provide valuable information on the unitarity triangle. The parity-violating asymmetry also gets a contribution from Feynman diagrams with two-photon intermediate states