Abstract
The result of a search for the pair production of the lightest supersymmetric partner of the bottom quark left({tilde{b}}_1right) using 139 fb−1 of proton-proton data collected at sqrt{s} = 13 TeV by the ATLAS detector is reported. In the supersymmetric scenarios considered both of the bottom-squarks decay into a b-quark and the second-lightest neutralino, {tilde{b}}_1to b+{tilde{chi}}_2^0 . Each {tilde{chi}}_2^0 is assumed to subsequently decay with 100% branching ratio into a Higgs boson (h) like the one in the Standard Model and the lightest neutralino: {tilde{chi}}_2^0to h+{tilde{chi}}_1^0 . The {tilde{chi}}_1^0 is assumed to be the lightest supersymmetric particle (LSP) and is stable. Two signal mass configurations are targeted: the first has a constant LSP mass of 60 GeV; and the second has a constant mass difference between the {tilde{chi}}_2^0 and {tilde{chi}}_1^0 of 130 GeV. The final states considered contain no charged leptons, three or more b-jets, and large missing transverse momentum. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered. Limits at the 95% confidence level are placed in the supersymmetric models considered, and bottom-squarks with mass up to 1.5 TeV are excluded.
Highlights
Background estimationThere are two main SM backgrounds which are expected to contribute to the yields for the signal regions (SRs) introduced in the previous section
All simulated events include a modelling of contributions from pile-up by overlaying minimumbias pp interactions from the same and nearby bunch crossings simulated in PYTHIA v8.186 and EvtGen v1.2.0 with the A3 [72] tune and the NNPDF2.3 leading order (LO) set [43]
In case of ∆m(χ02, χ01) = 130 GeV, bottom-squark masses up to 1.3 TeV are excluded for χ02 masses up to 750 GeV
Summary
The ATLAS detector [30] is a multipurpose particle physics detector with a forwardbackward symmetric cylindrical geometry and nearly 4π coverage in solid angle. The inner tracking detector consists of pixel and silicon microstrip detectors covering the pseudorapidity region |η| < 2.5, surrounded by a transition radiation tracker which enhances electron identification in the region |η| < 2.0. The inner tracking detector consists of pixel and silicon microstrip detectors covering the pseudorapidity region |η| < 2.5, surrounded by a transition radiation tracker which enhances electron identification in the region |η| < 2.0. The inner detector 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 regions (1.5 < |η| < 4.9) of the hadronic calorimeter are made of LAr active layers with either copper or tungsten as the absorber material. Three layers of high-precision tracking chambers provide coverage in the range |η| < 2.7, while dedicated fast chambers allow triggering in the. The ATLAS trigger system consists of a hardware-based level-1 trigger followed by a software-based high-level trigger [33]
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