Search for Bs --> mu+ mu- and other exclusive B decays with the ATLAS detector.

The ATLAS experiment, collecting data in pp collisions at the Large Hadron Collider (LHC), allows a variety of B-physics measurements. In this note we focus on exclusive B decays with J/psi -->mu+ mu- in the final state and on the search for the decay Bs --> mu+ mu-. Using 2.4 fb^{-1} of data collected in the first half of 2011, ATLAS set an upper limit on the branching fraction of BR(Bs --> mu+ mu-) < 2.2x10^{-8} at 95% confidence level. By combining this result with the corresponding search with CMS and LHCb detectors the observed number of events is in agreement with the background plus Standard Model signal expectation within 1 sigma and the corresponding upper limit to the brancing fraction is 4.2x10^{-9} at 95% CL.