Abstract
An inclusive search is performed for supersymmetry in final states containing jets and an apparent imbalance in transverse momentum, pt[miss], due to the production of unobserved weakly interacting particles in pp collisions at a centre-of-mass energy of 8 TeV. The data, recorded with the CMS detector at the CERN LHC, correspond to an integrated luminosity of 18.5 inverse femtobarns. The dimensionless kinematic variable alpha[T] is used to discriminate between events with genuine pt[miss] associated with unobserved particles and spurious values of pt[miss] arising from jet energy mismeasurements. No excess of event yields above the expected standard model backgrounds is observed. The results are interpreted in terms of constraints on the parameter space of several simplified models of supersymmetry that assume the pair production of top squarks. The search provides sensitivity to a broad range of top squark decay modes, including the two-body decay top squark to c chi0, where c is a charm quark and chi0 is the lightest neutralino, as well as the four-body decay top squark to b f f' chi0, where b is a bottom quark and f and f' are fermions produced in the decay of an intermediate off-shell W boson. These modes dominate in scenarios in which the top squark and lightest neutralino are nearly degenerate in mass. For these modes, top squarks with masses as large as 260 and 230 GeV are excluded, respectively, for the two- and four-body decays.
Highlights
The standard model (SM) is widely regarded as an effective approximation, valid at low energies, of a more complete theory of particle interactions, such as supersymmetry (SUSY) [1,2,3,4,5,6,7,8], which would supersede the SM at higher energy scales
While the search results can be interpreted with a broad range of models involving the strong production of coloured sparticles leading to final states with both low and high b quark content, we focus on the parameter space of simplified models [58,59,60] that assumes the pair production of top squarks, including the nearly mass-degenerate scenarios described above
The SM expectations in the signal region are related to the expected yields in the μ + jets, μμ + jets, and γ + jets control samples via the transfer factors derived from simulation
Summary
The standard model (SM) is widely regarded as an effective approximation, valid at low energies, of a more complete theory of particle interactions, such as supersymmetry (SUSY) [1,2,3,4,5,6,7,8], which would supersede the SM at higher energy scales. This topology is exploited by searches that consider “monojet” + pmT iss final states [21,22,23]. An event veto based on isolated tracks is used to further suppress SM background contributions from τ → hadrons + ν decays and misreconstructed electrons and muons These features yield an increased experimental acceptance to events with low jet activity, and improvements in the control of SM backgrounds, which are crucial for enhancing sensitivity to new sources of physics with nearly degenerate mass spectra
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