Lifetime differences and CP violation parameters of neutral B mesons at the next-to-leading order in QCD

We compute the next-to-leading order QCD corrections to the off-diagonal elements of the decay-width matrix Gamma entering the neutral B-meson oscillations. From this calculation the width differences DeltaGamma and the CP violation parameters (q/p) of B-d and B-s mesons are estimated, including the complete O(alpha(s)) QCD corrections and the 1/m(b) contributions. For the width difference DeltaGamma(s) we agree with previous results. By using the lattice determinations of the relevant hadronic matrix elements we obtain the theoretical predictions DeltaGamma(d)/Gamma(d) = (2.42 +/- 0.59) x 10(-3) and DeltaGamma(s)/Gamma(s) = (7.4 +/- 2.4) x 10(-2). For the CP violation parameters, we find (q/p)(d)\ - 1 = (2.96 +/- 0.67) x 10(-4) and (q/p)(s) - 1 = - (1.28 +/- 0.27) x 10(-5). These predictions are compatible with the experimental measurements which, however, suffer at present from large uncertainties.