Probing New Physics through B Mixing: Status, Benchmarks and Prospects

As is well known, $B^0_{d,s}$--$\bar B^0_{d,s}$ mixing offers a profound probe into the effects of physics beyond the Standard Model. The data obtained at the $e^+e^-$ $B$ factories have already provided valuable insights into the $B_d$-meson system, and very recently also the $B^0_s$--$\bar B^0_s$ oscillation frequency $\Delta M_s$ has been measured at the Tevatron. We give a critical discussion of the interpretation of these data in terms of model-independent new-physics parameters. We address in particular the impact of the uncertainties of the relevant input parameters, set benchmarks for their accuracies as required by future precision measurements at the LHC, and explore the prospects for new CP-violating effects in the $B_s$ system. To complement our model-independent analysis, we also discuss the constraints imposed by the CDF measurement of $\Delta M_s$ on popular models of new physics, namely scenarios with an extra $Z'$ boson and supersymmetry. We find that the new data still leave sizeable room for new-physics contributions to $B^0_{s}$--$\bar B^0_{s}$ mixing, which could be detected at the LHC.