PARITY-VIOLATING LONGITUDINAL MUON POLARIZATION IN K+-]PI+MU+MU- BEYOND LEADING LOGARITHMS

We generalize the existing analyses of the parity violating muon polarization asymmetry DELTA(LR) in K+ --> pi+ mu+ mu- beyond the leading logarithmic approximation. The inclusion of next-to-leading QCD corrections reduces the residual dependence on the renormalization scales, which is quite pronounced in the leading order. This leads to a considerably improved accuracy in the perturbative calculation of the short distance dominated quantity DELTA(LR). Accordingly this will also allow to obtain better constraints on the Wolfenstein parameter rho from future measurements of DELTA(LR). For -0.25 less-than-or-equal-to rho less-than-or-equal-to 0.25, V(cb) = 0.040 +/- 0.004 and m(t) = (170 +/- 20) GeV we find 3.0. 10(-3) less-than-or-equal-to \DELTA(LR)\ less-than-or-equal-to 9.6 . 10(-3).