  Studies of rare decays play an important role in the search of physics beyond
the standard model. New particles may participate in the loop processes and can
be probed by seeing any deviations from the standard model predictions. The
very rare decay $B_s\to\mu^+\mu^-$ has been observed with the data collected by
CMS and LHCb experiments. The signal seen by the ATLAS experiment is less
significant but is compatible with the predictions. The measurement itself
provides stringent constraints to new physics models. The first effective
lifetime measurement with $B_s\to\mu^+\mu^-$ candidates has been carried out by
the LHCb experiment. More data are still required to observe the
$B^0\to\mu^+\mu^-$ decays. The $B\to K^*\mu^+\mu^-$ decay also proceeds through
a flavour changing neutral current process, and is sensitive to the new
physics. Extended measurements are carried out for $B\to K^*\mu^+\mu^-$ decays.
Most of the classical physics parameters are found to be consistent with the
predictions, but tensions do emerge in some of the observables. More data will
help to clarify these potential deviations.
