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Theoretical update of Bs mixing

Lenz, Alexander; Nierste, Ulrich


Alexander Lenz

Ulrich Nierste


We update the theory predictions for the mass difference ΔMs, the width difference ΔΓs and the CP asymmetry in flavour-specific decays, afss, for the Bs−bar Bs system. In particular we present a new expression for the element Γ12s of the decay matrix, which enters the predictions of ΔΓs and afss. To this end we introduce a new operator basis, which reduces the troublesome sizes of the 1/mb and αs corrections and diminishes the hadronic uncertainty in ΔΓs/ΔMs considerably. Logarithms of the charm quark mass are summed to all orders. We find ΔΓs/ΔMs = (49.7±9.4)bold dot10−4 and ΔΓs = (fBs/240 MeV)2[(0.105±0.016) B + (0.024±0.004) tilde BS' − 0.027±0.015] ps−1 in terms of the bag parameters B, tilde BS' in the NDR scheme and the decay constant fBs. The improved result for Γ12s also permits the extraction of the CP-violating Bs−bar Bs phase from afss with better accuracy. We show how the measurements of ΔMs, ΔΓs, afss, ACPmix(Bs→J/ψphgr) and other observables can be efficiently combined to constrain new physics. Applying our new formulae to data from the DØ experiment, we find a 2σ deviation of the Bs−bar Bs phase from its Standard Model value. We also briefly update the theory predictions for the Bd−bar Bd system and find ΔΓd/ΔMd = (52.6+11.5−12.8) bold dot10−4 and afsd = (−4.8+1.0−1.2) bold dot10−4 in the Standard Model.


Lenz, A., & Nierste, U. (2007). Theoretical update of Bs mixing. Journal of High Energy Physics, 2007(06), Article 072.

Journal Article Type Article
Acceptance Date Dec 7, 2015
Publication Date Jun 1, 2007
Deposit Date Dec 7, 2015
Publicly Available Date Feb 24, 2016
Journal Journal of High Energy Physics
Print ISSN 1126-6708
Electronic ISSN 1029-8479
Publisher Scuola Internazionale Superiore di Studi Avanzati (SISSA)
Peer Reviewed Peer Reviewed
Volume 2007
Issue 06
Article Number 072


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