A Search for Lepton-Jets with Muons at ATLAS

We present a search for a new, light (∼1 GeV) boson decaying to muons in a final state consisting of collimated leptons (lepton-jets). The analysis is performed on 40 pb−1 of data collected by the ATLAS detector at the Large Hadron Collider with sqrt(s) = 7 TeV. Events are required to contain at least two isolated lepton-jets, each of which must contain at least two muons. We observe 0 candidate events after all cuts, while expecting 0.21 +- 0.19 background events. From this, we set 95% C.L. limits on the cross section for supersymmetric events with the lightest supersymmetric particle decaying to the new boson, as a function of the new boson’s mass.