Theoretical update of $B$-Mixing and Lifetimes

TL;DR

This paper reviews the current theoretical understanding of B-meson mixing and lifetimes, compares predictions with recent precise experimental data, confirms the validity of the Heavy Quark Expansion, and discusses potential for new physics detection.

Contribution

It provides a comprehensive update on B-mixing and lifetimes, validating theoretical tools with recent measurements and exploring model-independent new physics search strategies.

Findings

Heavy Quark Expansion agrees with data within 30% accuracy.

B_s and B_d lifetime ratios match theoretical expectations.

No deviations from the Standard Model observed yet.

Abstract

We review the current status of theoretical predictions for mixing quantities and lifetimes in the $B$-sector. In particular, due to the first non-zero measurement of the decay rate difference in the neutral $B_s$-system, $\Delta \Gamma_s/ \Gamma_s = 17.6 % \pm 2.9 %$ by the LHCb collaboration and very precise data for $\tau_{B_s}$ from TeVatron and LHCb our theoretical tools can now be rigorously tested and it turns out that the Heavy Quark Expansion works in the $B$-system to an accuracy of at least 30% for quantities like $\Gamma_{12}$, which is most sensitive to hypothetical violations of quark hadron duality. This issue that gave rise in the past to numerous theoretical papers, has now been settled experimentally. Further data will even allow to shrink this bound. For total inclusive quantities like lifetimes the compliance is even more astonishing: $\tau_{B_s}^{\rm LHCb}/ \tau_{B_d}^{\rm HFAG} = 1.001 \pm 0.014$ is in perfect agreement with the theory expectation of $\tau_{B_s}/\tau_{B_d} = 0.996 ... 1.000$. Despite the fact that the new data show no deviations from the standard model expectations, there is still some sizable room for new physics effects. Model-independent search strategies for these effects are presented with an emphasis on the interconnection with many different observables that have to be taken into account. In that respect a special emphasis is given to the large value of the di-muon asymmetry measured by the D0 collaboration.