Dimuon composition in ATLAS at 7 TeV

We present a determination of the π and K contributions to the invariant mass spectrum of di-muon events up to 150 GeV in collision data collected by the ATLAS experiment at √s = 7 TeV. These processes contribute to the backgrounds to searches for physics beyond the Standard Model where the signal has two or more muons in the final state. The analysis is based on a total integrated luminosity of 1.5 pb−1, using muons with transverse momentum larger than 3 GeV and pseudorapidity |η| < 1.05. The fractions of di-muon events which contain at least one muon from π or K decay are (31 ± 4)% and (68 ± 3)% for μ+ μ− and μ± μ± events, respectively.