Institute for Theoretical Particle Physics (TTP)

TTP06-16 Charm Quark Contribution to K_L -> mu^+ mu^- at Next-to-Next-to-Leading Order

TTP06-16 Charm Quark Contribution to K_L -

TTP06-16 Charm Quark Contribution to K_L -

mu^+ mu^- at Next-to-Next-to-Leading Order > We calculate the charm quark contribution to the decay K_L → mu^+ mu^- in next-to-next-to-leading order of QCD. This new contribution reduces the theoretical uncertainty in the relevant parameter P_c from +/-22% down to +/-7%, corresponding to scale uncertainties of +/-3% and +/-6% in the short-distance part of the branching ratio and the determination of the Wolfenstein parameter rhobar from K_L → mu^+ mu^-. The error in P_c = 0.115 +/- 0.018 is now in equal shares due to the combined scale uncertainties and the current uncertainty in the charm quark mass. We find BR (K_L → mu^+ mu^-)_SD = (0.79 +/- 0.12) x 10^-9, with the present uncertainty in the Cabibbo-Kobayashi-Maskawa matrix element V_td being the dominant individual source in the quoted error.

Martin Gorbahn and Ulrich Haisch
Phys. Rev. Lett. 97 122002 2006
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