Search for top squark pair production in compressed-mass-spectrum scenarios in proton-proton collisions at sqrt(s) = 8 TeV using the alpha[T] variable

TL;DR

This paper reports a search for top squark pair production in compressed-mass-spectrum scenarios at 8 TeV using the alpha[T] variable, finding no excess and setting mass exclusion limits up to 260 GeV.

Contribution

It introduces a novel analysis using the alpha[T] variable to improve sensitivity to compressed supersymmetry scenarios at the LHC.

Findings

No excess observed above standard model backgrounds.

Excluded top squark masses up to 260 GeV for specific decay modes.

Sensitive to a broad range of decay channels in compressed spectra.

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.