Abstract
A search for heavy charged long-lived particles is performed using a data sample of 36.1 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model-independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks ($R$-hadrons), charginos and staus. No significant deviations from the expected Standard Model background are observed. Upper limits at 95% confidence level are provided on the production cross sections of long-lived $R$-hadrons as well as directly pair-produced staus and charginos. These results translate into lower limits on the masses of long-lived gluino, sbottom and stop $R$-hadrons, as well as staus and charginos of 2000 GeV, 1250 GeV, 1340 GeV, 430 GeV and 1090 GeV, respectively.
Highlights
The search for heavy charged long-lived particles presented in this paper is based on a dpataffiffi sample of 36.1 fb−1 of proton-proton collisions at s 1⁄4 13 TeV collected in 2015 and 2016
It utilizes observables related to large ionization energy loss and time of flight (ToF), which are signatures of heavy charged particles traveling significantly slower than the speed of light
The ATLAS detector [30] is a multipurpose particle detector consisting of the inner tracking detector (ID) immersed in a 2 T solenoidal magnetic field, electromagnetic as well as hadronic calorimeters and a muon spectrometer (MS) based on three large air-core toroid superconducting magnets with eight coils each
Summary
The search for heavy charged long-lived particles presented in this paper is based on a dpataffiffi sample of 36.1 fb−1 of proton-proton (pp) collisions at s 1⁄4 13 TeV collected in 2015 and 2016. Through hadronic interactions of the light-quark constituents with the detector material, especially inside the calorimeters, R-hadrons can change to states with a different electric charge. Results for pair-produced charginos are motivated by a minimal anomaly-mediated supersymmetry breaking (mAMSB) model, where often the supersymmetric partners of the SM W-boson fields, the wino fermions, are the lightest gaugino states. In this particular case, the lightest of the charged mass eigenstates, a chargino, and the lightest of the neutral mass eigenstates, a neutralino, are both almost pure wino and nearly mass-degenerate, resulting in longlived charginos
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