Next-to-Leading Order QCD corrections to the Lifetime Difference of Bs Mesons

In this talk we present a calculation of the dacay rate difference in the neutral Bs − Bs system, ∆ΓBs , in next-to-leading order (NLO) QCD. We find a sizeable decrease compared to leading-order (LO) estimates: (∆Γ/Γ)Bs = (fBs/210MeV ) [0.006B(mb)+0.150BS(mb)−0.0063] in terms of the bag parameters B and BS in the NDR scheme. We put special emphasize on the theoretical and physical implications of this quantity. 1. Non-expert-introduction As there were many students in the audience we will start with an elementary introduction. Neutral mesons are well known from lectures at the university and were mentioned here several times e.g. in [1, 2, 3, 4]. As in the K-system we have in the Bs-system flavour eigenstates which are defined by their quark content. |Bs〉 = (b̄s) ; |Bs〉 = (bs̄) . (1.1) The mass eigenstates are linear combinations of the flavour eigenstates |BH〉 = p|Bs〉 − q|Bs〉 (1.2) |BL〉 = p|Bs〉+ q|Bs〉 (1.3) with the normalization condition |p|2 + |q|2 = 1. BH and BL are the physical states. They have definite masses and lifetimes, but no definte CPquantum numbers. The mass eigenstates are in in collaboration with Martin Beneke, Theory Division, CERN, CH-1211 Geneva 23, Switzerland; Gerhard Buchalla, Theory Division, CERN, CH-1211 Geneva 23, Switzerland; Christoph Greub, Institut für Theoretische Physik, Universität Bern, Sidlerstrasse 5, CH-3012 Berne, Switzerland; Ulrich Nierste, Fermilab, Theory Division MS106, IL-60510-500, USA. general mixtures of CP-odd and CP-even eigenstates. The time evolution of the physical states is described by a simple Schrödinger equation i∂t ~ B = Ĥ ~ B (1.4)