  A search for groups of collimated muons is performed using a data sample
collected by the CMS experiment at the LHC, at a centre-of-mass energy of 7
TeV, and corresponding to an integrated luminosity of 35 inverse picobarns. The
analysis searches for production of new low-mass states decaying into pairs of
muons and is designed to achieve high sensitivity to a broad range of models
predicting leptonic jet signatures. With no excess observed over the background
expectation, upper limits on the production cross section times branching
fraction times acceptance are set, ranging from 0.1 to 0.5 pb at the 95% CL
depending on event topology. In addition, the results are interpreted in
several benchmark models in the context of supersymmetry with a new light dark
sector exploring previously inaccessible parameter space.
