Abstract
A search is presented for direct chargino production based on a disappearing-track signature using 20.3 fb-1 of proton-proton collisions at sqrt(s) = 8 TeV collected with the ATLAS experiment at the LHC. In anomaly-mediated supersymmetry breaking (AMSB) models, the lightest chargino is nearly mass-degenerate with the lightest neutralino and its lifetime is long enough to be detected in the tracking detectors by identifying decays that result in tracks with no associated hits in the outer region of the tracking system. Some models with supersymmetry also predict charginos with a significant lifetime. This analysis attains sensitivity for charginos with a lifetime between 0.1 ns and 10 ns, and significantly surpasses the reach of the LEP experiments. No significant excess above the background expectation is observed for candidate tracks with large transverse momentum, and constraints on chargino properties are obtained. In the AMSB scenarios, a chargino mass below 270 GeV is excluded at 95% confidence level.
Highlights
Anomaly-mediated supersymmetry breaking (AMSB) models [1,2], where soft supersymmetry (SUSY) breaking is caused by loop effects, provide a constrained mass spectrum of SUSY particles
The inside-out sequence is of particular interest for finding long-lived chargino trajectories, it is optimized for the reconstruction of stable particles that leave long tracks in the inner detector (ID), and, in particular, only reconstructs tracks with a minimum of seven space points
The calculation of EmT iss is based on the transverse momenta of remaining jets and lepton candidates and on all calorimeter energy clusters that are not associated with such objects [29]
Summary
Anomaly-mediated supersymmetry breaking (AMSB) models [1,2], where soft supersymmetry (SUSY) breaking is caused by loop effects, provide a constrained mass spectrum of SUSY particles. Several other SUSY models, which are motivated by the large value of the Higgs boson mass, predict charginos with a significant lifetime and their decay to a soft pion and the lightest supersymmetric particle [3,4,5,6]. The most significant improvement is achieved by enhancing the track reconstruction efficiency for charginos having short decay lengths. The present analysis provides sensitivity to a wider range of chargino lifetimes and covers a larger angular acceptance. It significantly surpasses the reach of the LEP experiments [9,10,11,12] for charginos with lifetimes >0:1 ns
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