LTP: Laboratory for Particle Physics

The Laboratory of Particle Physics (LTP) at the Paul Scherrer Institute pursues fundamental research, addressing the most up to date questions in modern physics. read more

Search for B_s → μ⁺μ^- decays in pp collisions at √s = 7 TeV

B_s mesons, composed of a 'beauty' and a 'strange' quark, are produced copiously at the LHC. The fraction that subsequently decays (known as the 'branching fraction') to a pair of muons is highly suppressed in the Standard Model - only about three such decays are expected per billion B_s meson produced. Several extensions of the SM, for instance supersymmetric models, predict (significant) enhancements of this branching fraction. CMS has searched for the decays of B_s to muon pairs using proton-proton collision data collected up to June 2011. The CMS (barrel) pixel detector, developed and constructed at PSI, has a central role in reconstructing the signal with high efficiency while strongly reducing the background. The number of candidate decays observed in the available data sample is consistent with the Standard Model expectations for signal and background. CMS has excluded (at 95% confidence level) branching fractions larger than 1.9e-8 for the decay B_s → μ⁺μ^-. This result is among the most stringent exclusion limits achieved until now and implies significant constraints on extensions of the Standard Model. The CMS result has been accepted for publication in PRL and has been combined with the corresponding result of the LHCb collaboration.