Abstract
A search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment in sqrt{s}=13~{mathrm{TeV}} proton–proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 3.2 mathrm{fb}^{-1} of analyzed data. Results are interpreted within simplified models that assume R-parity is conserved and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95 % confidence level on the mass of the gluino is set at 1.51 {mathrm{TeV}} for a simplified model incorporating only a gluino octet and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.03 {mathrm{TeV}} are excluded for a massless lightest neutralino. These limits substantially extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
Highlights
Background estimation and validationStandard Model background processes contribute to the event counts in the signal regions
The multi-jet background is generated with Pythia 8.186 using the A14 underlying-event tune and the NNPDF2.3LO parton distribution functions
Events with jets originating from detector noise and non-collision background are rejected if the jets fail to satisfy the ‘LooseBad’ quality criteria, or if at least one of the two leading jets with pT > 100 GeV fails to satisfy the ‘TightBad’ quality criteria, both described in Ref. [79]
Summary
The ATLAS detector [26] is a multi-purpose detector with a forward-backward symmetric cylindrical geometry and nearly 4π coverage in solid angle. The inner tracking detector (ID) consists of pixel and silicon microstrip detectors covering the pseudorapidity region |η| < 2.5, surrounded by a transition radiation tracker which improves electron identification over the region |η| < 2.0. The inner tracking detector (ID) consists of pixel and silicon microstrip detectors covering the pseudorapidity region |η| < 2.5, surrounded by a transition radiation tracker which improves electron identification over the region |η| < 2.0. A steel/scintillator-tile calorimeter provides hadronic coverage in the central pseudorapidity range (|η| < 1.7). Three layers of high-precision tracking chambers provide coverage in the range |η| < 2.7, while dedicated chambers allow triggering in the region |η| < 2.4. Auxiliary data samples used to estimate the yields of background events were selected using triggers requiring at least one isolated electron ( pT > 24 GeV), muon ( pT > 20 GeV) or photon ( pT > 120 GeV). To increase the efficiency at high momenta, additional single-electron and single-muon triggers that do not require any isolation were included with thresholds of pT = 60 GeV and pT = 50 GeV, respectively. It is derived, following a methodology similar to that detailed in Ref. [29], from a preliminary calibration of the luminosity scale using a pair of x–y beam-separation scans performed in August 2015
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