Abstract
A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an $R$-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a $b$-jet. The dataset corresponds to an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a $b$-quark.
Highlights
The extension of the Standard Model (SM) of particle physics with supersymmetry (SUSY) [1,2,3,4,5,6] leads to processes that violate both baryon number (B) and lepton number (L), such as rapid proton decay
Each control region is defined to be kinematically close to the SRs while inverting or relaxing specific selections to enhance the contribution from the targeted background process while reducing the contamination from other backgrounds and the benchmark signals
This paper presents the first ATLAS results on the search for the pair production of stops, each decaying via an R-parity-violating coupling to a b-quark and a lepton
Summary
The extension of the Standard Model (SM) of particle physics with supersymmetry (SUSY) [1,2,3,4,5,6] leads to processes that violate both baryon number (B) and lepton number (L), such as rapid proton decay. The minimal supersymmetric extension only needs a vacuum expectation value for a right-handed scalar neutrino in order to spontaneously break the B − L symmetry [14,15,16,17,18] This minimal B − L model violates lepton number but not baryon number. At the LHC, the most noticeable effect is that the LSP is no longer stable and can decay via RPV processes, and it may carry color and electric charge This leads to unique signatures that are forbidden in conventional models with R-parity conservation.
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