Narrow Results

The highlights and conflicts at the B factories are briefly reviewed. CP violation was established in 2001 in B⁰→J/ψK_S and related modes, which has now become a precision measurement of CP violation in mixing. However, the situation for the B⁰→π⁺π^- and charmless b→s modes, which also probe CP violation in the decay amplitude, are not quite settled yet. They could be hinting at the presence of both strong (CP conserving) and new physics (CP violating) phases. We critically assess the developments and discuss some related discrepancies and highlights, such as observation of direct CP violation, and make a projection towards the next few years.

Recent experimental measurements and lattice QCD calculations are now reaching the precision (and accuracy) needed to over-constrain the CKM parameters and . In this brief review, we discuss the current status of lattice QCD calculations needed to connect the experimental measurements of B meson properties to quark flavor-changing parameters. Special attention is given to B→πℓν, which is becoming a competitive way to determine |V_ub|, and to mixings, which now include reliable extrapolation to the physical light quark mass. The combination of the recent measurement of the B_s mass difference and current lattice calculations dramatically reduces the uncertainty in |V_td|. We present an outlook for reducing dominant lattice QCD uncertainties entering CKM fits and remark on lattice calculations for other decay channels.

In this short review we present the history, an overview of the analysis, and some personal comments on the anomalous like-sign dimuon charge asymmetry measurements by the DØ collaboration.

Results on $B\to {\mu }^{+}{\mu }^{-}$ decays with the CMS experiment are reported, using 61 fb${}^{-1}$ of data recorded during LHC Run 1 and 2016. With an improved muon identification algorithm and refined unbinned maximum likelihood fitting methods, the decay $B_s^0\to {\mu }^{+}{\mu }^{-}$ is observed with a significance of 5.6 standard deviations. Its branching fraction is measured to be $\overline{{ℬ}}(B_s^0\to {\mu }^{+}{\mu }^{-})=[2.9\pm 0.7(exp)\pm 0.2(\mathrm{\text{frag}})]\times 10^{-9}$, where the first error is the combined statistical and systematic uncertainty and the second error quantifies the uncertainty of the $B_s^0$ and $B^{+}$ fragmentation probability ratio. The $B_s^0\to {\mu }^{+}{\mu }^{-}$ effective lifetime is ${\tau }_{{\mu }^{+}{\mu }^{-}}=1.70_{-0.44}^{+0.61}\mathrm{\text{ps}}$. No evidence for the decay $B^0\to {\mu }^{+}{\mu }^{-}$ is found and an upper limit of ${ℬ}(B^0\to {\mu }^{+}{\mu }^{-})<3.6\times 10^{-10}$ (at 95% confidence level) is determined. All results are consistent with the standard model of particle physics.