We present a search for a light (mass < 2 GeV) boson predicted by Hidden Valley supersymmetric models that decays into a final state consisting of collimated muons or electrons, denoted "lepton-jets". The analysis uses 5 fb(-1) of root s = 7 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider to search for the following signatures: single lepton-jets with at least four muons; pairs of lepton-jets, each with two or more muons; and pairs of lepton-jets with two or more electrons. This study finds no statistically significant deviation from the Standard Model prediction and places 95% confidence-level exclusion limits on the production cross section times branching ratio of light bosons for several parameter sets of a Hidden Valley model.
Wemans, A. J. M. L. D. V., & ATLAS Collaboration (2013). A search for prompt lepton-jets in pp collisions at root s=7 TeV with the ATLAS detector. Physics Letters B, 719(4-5), 299-317. https://doi.org/10.1016/j.physletb.2013.01.034