Abstract
The results of a search for the stop, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, jets, and missing transverse momentum are reported. The search uses the 2015 LHC $pp$ collision data at a center-of-mass energy of $\sqrt{s}=13$ TeV recorded by the ATLAS detector and corresponding to an integrated luminosity of 3.2 fb${}^{-1}$. The analysis targets two types of signal models: gluino-mediated pair production of stops with a nearly mass-degenerate stop and neutralino; and direct pair production of stops, decaying to the top quark and the lightest neutralino. The experimental signature in both signal scenarios is similar to that of a top quark pair produced in association with large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits on gluino and stop masses are set at 95% confidence level. The results extend the LHC Run-1 exclusion limit on the gluino mass up to 1460 GeV in the gluino-mediated scenario in the high gluino and low stop mass region, and add an excluded stop mass region from 745 to 780 GeV for the direct stop model with a massless lightest neutralino. The results are also reinterpreted to set exclusion limits in a model of vector-like top quarks.
Highlights
Supersymmetry (SUSY) [1–6] is a natural solution [7,8] to the hierarchy problem [9–12]
Samples of Monte Carlo (MC) simulated events are used for the description of the background and to model the SUSY signals
All samples are produced with varying numbers of simulated minimum-bias interactions generated with PYTHIA 8 overlaid on the hard-scattering event to account for pileup from multiple pp interactions in the same or nearby bunch crossings
Summary
Supersymmetry (SUSY) [1–6] is a natural solution [7,8] to the hierarchy problem [9–12]. The former scenario refers to pair production of gluinos, each decaying to the top quark and the ~t1. The visible ~t1 decay products have low momentum, typically below the reconstruction and identification thresholds This scenario is motivated by the dark matter relic density, which is generally too large in the Minimal Supersymmetric Standard Model [22,23] but can be regulated by coannihilation of the top squark and the neutralino [24].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
