====== TTP06-16 Charm Quark Contribution to K_L -> mu^+ mu^- at Next-to-Next-to-Leading Order ======
 
 
<hidden 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.
 </hidden>
|**Martin Gorbahn and Ulrich Haisch**  | 
|**  Phys. Rev. Lett.  97 122002 2006  **  |
| {{preprints:2006:ttp06-16.pdf|PDF}} {{preprints:2006:ttp06-16.ps|PostScript}}   |
| |