Speaker
Robert Fleischer
(Nikhef and Vrije Universiteit Amsterdam)
Description
The rare decay $B_s \to \mu^+\mu^-$ plays a key role for the testing of the Standard Model. It is discussed that the sizable decay width difference $\Delta\Gamma_s$ of the $B_s$-meson system affects this channel. As a consequence, its calculated Standard Model branching ratio has to be upscaled by about 10% to $(3.56\pm0.18)\times 10^{-9}$. This prediction is the reference value for the comparison with the time-integrated experimental branching ratio, where LHCb has recently reported $(3.2^{+1.5}_{-1.2})\times10^{-9}$ corresponding to the first evidence for $B_s\to \mu^+\mu^-$. The sizable $\Delta\Gamma_s$ makes a new observable through the effective $B_s\to \mu^+\mu^-$ lifetime accessible, which probes New Physics in a way complementary to the branching ratio and adds an exciting new topic to the agenda for the high-luminosity upgrade of the LHC.
Further probes of New Physics are offered by a CP-violating rate asymmetry. Correlations between these observables and the
$B_s \to \mu^+\mu^-$ branching ratio are illustrated for specific models of New Physics.
Author
Robert Fleischer
(Nikhef and Vrije Universiteit Amsterdam)
