Search for New Physics with rare decays of $B^0, B^+$ and $B^0_s$ mesons at LHCb

The rare processes $b \to s\ell^{+}\ell^{-}$ and $b \to s\gamma$ are flavour changing neutral currents that are forbidden at tree level in the Standard Model (SM). They can proceed via higher order electroweak ($Z^0, \gamma$) penguin or box diagrams. In extensions to the SM, new virtual particles can enter at loop level, leading to significant deviations from the SM predictions. These deviations may be the enhancement (or suppression) of branching fractions, where a good example, the search for the very rare decays $B^0_{(s)} \to \mu^{+}\mu^{-}$ is presented here. They might also be observable in the modification of angular distributions, e.g. in $B^0 \to K^{*} \mu^{+}\mu^{+}$, or in the modification of $CP$ or Isospin asymmetries such as those observable in the radiative decays $B^0 \to K^{*\gamma}$ and $B^0_s \to \phi\gamma$. The last presented probe extensions to the SM is the search for Majorana neutrinos in same sign decays of $B^+ \to h^{-}\mu^{+}\mu^{1}$ where $h^{-}$ represents a $K^{-}$ or $\pi^{-}$. These rare decay processes provide a complementary approach to direct searches at the general purpose detectors and can provide sensitivity to new particles with masses up to higher scales than directly accessible. At the time of the conference Physics at LHC 2011 (PLHC), June 2011, a published LHCb measurement of the search for the very rare decays $B^0_{(s)} \to \mu^{+}\mu^{-}$ using 37 pb$^{-1}$ existed[1]. The angular analysis of $B^0 \to K^{*}\mu^{+}\mu^{-}$ as well as the radiative decay measurements were in preparation for the EPS conference in July 2011. In the meantime, these three measurements have been performed using about 300pb$^{-1}$ of data. Hence, these proceedings describe the existing measurements [2,3,4] rather than an outdated status at the time of PLHC. The Majorana neutrino search was presented for the first time at PLHC.