Search for supersymmetry in events with soft leptons, low jet multiplicity, and missing transverse momentum in proton-proton collisions at sqrt(s) = 8 TeV

A search for supersymmetry with a compressed mass spectrum is presented. Events are selected using the presence of a high-momentum jet from initial state radiation, high missing energy, and a low-momentum muon, either as the only lepton in the event or accompanied by an electron or muon of the opposite charge. In particular, a scenario of top squark pair production is investigated, where the mass difference to the lightest supersymmetric particle (LSP) is smaller than the mass of the W~boson. In this case the top squarks could undergo four-body decays to $\mathrm{b} \ell \nu + \mathrm{LSP}$. The search is performed in a sample of proton-proton collisions recorded with the CMS detector at a centre-of-mass energy of 8\,TeV and corresponding to an integrated luminosity of 19.7\,$\mathrm{fb}^{-1}$. The results are consistent with the expectation from standard model processes and limits are set on the production cross section in the plane of the top squark vs. LSP masses. Assuming a 100\% branching ratio of the four-body decay top squark masses below 316\,GeV are excluded at 95\%~confidence level for a mass difference to the LSP of about 25\,GeV. Results are also interpreted under the assumption of chargino-neutralino production, with subsequent decays via sleptons or sneutrinos.