Abstract
A search for new phenomena in final states containing an e^+e^- or mu ^+mu ^- pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton–proton collision data with an integrated luminosity of 36.1~mathrm {fb}^{-1}, collected during 2015 and 2016 at a centre-of-mass energy sqrt{s} = 13~hbox {TeV} with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an e^+e^- or mu ^+mu ^- pair and the lightest neutralino (tilde{chi }_1^0) via one of two next-to-lightest neutralino (tilde{chi }_2^0) decay mechanisms: tilde{chi }_2^0 rightarrow Z tilde{chi }_1^0, where the Z boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the Z boson mass; and tilde{chi }_2^0 rightarrow ell ^+ell ^- tilde{chi }_1^0 with no intermediate ell ^+ell ^- resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 and 1.3 text {Te}text {V} at 95% confidence level, respectively.
Highlights
Background estimationIn most signal regions (SRs), the dominant background processes are “flavour-symmetric” (FS), where the ratio of ee, μμ and eμ dileptonic branching fractions is expected to be 1:1:2 because the two leptons originate from independent W → ν decays
Model-independent upper limits at 95% confidence level (CL) on the number of events (S95) that could be attributed to non-SM sources are derived using the CLS prescription [96], implemented in the HistFitter program [97]
The exceptions are the statistical uncertainties in the flavour-symmetry method and Monte Carlo (MC)-based backgrounds, which are treated as Poissonian nuisance parameters
Summary
The ATLAS detector [16] is a general-purpose detector with almost 4π coverage in solid angle. The detector comprises an inner tracking detector, a system of calorimeters, and a muon spectrometer. The inner tracking detector (ID) is immersed in a 2 T magnetic field provided by a superconducting solenoid and allows charged-particle tracking out to |η| = 2.5. It includes silicon pixel and silicon microstrip tracking detectors inside a straw-tube tracking detector. The ATLAS detector has a two-level trigger system, with the first level implemented in custom hardware and the second level implemented in software. This trigger system reduces the output rate to about 1 kHz from up to 40 MHz [18]
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