Abstract
The results of a search for new phenomena in final states with b-jets and missing transverse momentum using 139 fb−1 of proton-proton data collected at a centre-of-mass energy sqrt{s} = 13 TeV by the ATLAS detector at the LHC are reported. The analysis targets final states produced by the decay of a pair-produced supersymmetric bottom squark into a bottom quark and a stable neutralino. The analysis also seeks evidence for models of pair production of dark matter particles produced through the decay of a generic scalar or pseudoscalar mediator state in association with a pair of bottom quarks, and models of pair production of scalar third-generation down-type leptoquarks. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered by the analysis. Bottom squark masses below 1270 GeV are excluded at 95% confidence level if the neutralino is massless. In the case of nearly mass-degenerate bottom squarks and neutralinos, the use of dedicated secondary-vertex identification techniques permits the exclusion of bottom squarks with masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV. These limits extend substantially beyond the regions of parameter space excluded by similar ATLAS searches performed previously.
Highlights
√ energy s = 13 TeV by the ATLAS detector at the LHC are reported
Previous searches by ATLAS [42,43,44,45] and CMS [46, 47] using comparable or smaller datasets have targeted similar final states. This analysis extends the regions of parameter space probed by the LHC through the use of a larger dataset than in previous ATLAS searches, new boosted decision tree (BDT) discriminants, and new selections maximising the efficiency for reconstructing b-jets with low transverse momentum generated by, for instance, SUSY models with small mass-splitting betweenb1 and χ01
Samples of bottom squark and dark matter signal events were generated with MadGraph5_aMC@next-to-leading order (NLO) 2.6.2 [58] at leading order (LO) in the strong coupling constant, with the renormalisation and factorisation scales set to HTgen/2 and parton distribution function (PDF) NNPDF2.3 LO [59]
Summary
The ATLAS detector [48,49,50] is a multipurpose detector with a forward-backward symmetric cylindrical geometry and nearly 4π coverage in solid angle. The inner detector (ID). Tracking system 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 ID is surrounded by a thin superconducting solenoid providing an axial 2 T magnetic field and by a fine-granularity lead/liquid-argon (LAr) electromagnetic calorimeter covering |η| < 3.2. A steel/scintillator-tile calorimeter provides hadronic coverage in the central pseudorapidity range (|η| < 1.7). The endcap and forward calorimeters (1.5 < |η| < 4.9) are made of LAr active layers with either copper or tungsten as the absorber material for electromagnetic and hadronic measurements. 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
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