Abstract
An updated search is performed for gluino, top squark, or bottom squark R-hadrons that have come to rest within the ATLAS calorimeter, and decay at some later time to hadronic jets and a neutralino, using 5.0 and 22.9 fb−1 of pp collisions at 7 and 8 TeV, respectively. Candidate decay events are triggered in selected empty bunch crossings of the LHC in order to remove pp collision backgrounds. Selections based on jet shape and muon system activity are applied to discriminate signal events from cosmic ray and beam-halo muon backgrounds. In the absence of an excess of events, improved limits are set on gluino, stop, and sbottom masses for different decays, lifetimes, and neutralino masses. With a neutralino of mass 100 GeV, the analysis excludes gluinos with mass below 832 GeV (with an expected lower limit of 731 GeV), for a gluino lifetime between 10 μs and 1000 s in the generic R-hadron model with equal branching ratios for decays to qq¯χ˜0 and gχ˜0. Under the same assumptions for the neutralino mass and squark lifetime, top squarks and bottom squarks in the Regge R-hadron model are excluded with masses below 379 and 344 GeV, respectively.4 MoreReceived 24 October 2013DOI:https://doi.org/10.1103/PhysRevD.88.112003This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2013 CERN, for the ATLAS Collaboration
Highlights
Long-lived massive particles appear in many theories beyond the Standard Model [1]
They are predicted in Rparity-conserving supersymmetry (SUSY) [2,3,4,5,6,7,8,9,10,11,12,13,14,15] models, such as split SUSY [16,17] and gauge-mediated SUSY breaking [18,19,20,21,22,23,24], as well as other scenarios such as universal extra dimensions [25] and leptoquark extensions [26]
The ATLAS detector [37] consists of an inner tracking system (ID) surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer (MS)
Summary
Long-lived massive particles appear in many theories beyond the Standard Model [1]. They are predicted in Rparity-conserving supersymmetry (SUSY) [2,3,4,5,6,7,8,9,10,11,12,13,14,15] models, such as split SUSY [16,17] and gauge-mediated SUSY breaking [18,19,20,21,22,23,24], as well as other scenarios such as universal extra dimensions [25] and leptoquark extensions [26]. Split SUSY addresses the hierarchy problem via the same fine-tuning mechanism that solves the cosmological constant problem; SUSY can be broken at a very high-energy scale, leading to heavy scalars, light fermions, and a light, finely tuned, Higgs boson [16] Within this phenomenological picture, squarks would be much heavier than gluinos, suppressing the gluino decay. ATLAS has up to now studied 31 pbÀ1 of data from 2010 [34], resulting in the limit mg~ > 341 GeV, under similar assumptions This analysis complements previous ATLAS searches for long-lived particles [35,36] that are less sensitive to particles with initial The search is sensitive to any new physics scenario producing large out-of-time energy deposits in the calorimeter with minimal additional detector activity
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