Extending The Limits In The Hunt For Long Lived Heavy Neutral Leptons With The Atlas Experiment At The Large Hadron Collider At Cern
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Extending the Limits in the Hunt for Long-lived Heavy Neutral Leptons with the ATLAS Experiment at the Large Hadron Collider at CERN
Englische Version: A search for a long-lived, heavy neutral lepton ($\mathcal{N}$) in 139~fb$ {-1}$ of $\sqrt{s}=13$~TeV $pp$ collision data collected between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider is presented. The $\mathcal{N}$ is assumed to be produced via $W \rightarrow \mathcal{N} \mu$ or $W \rightarrow \mathcal{N} e$ and decays into two charged leptons and a neutrino, forming a unique displaced vertex signature. A novel technique is used to reconstruct the $\mathcal{N}$ mass that discriminates between signal and background. No signal is observed, and limits are set on the squared mixing parameters of the $\mathcal{N}$ with the left-handed neutrino states for the $\mathcal{N}$ mass range $3$~GeV~$
Search for Massive, Long-lived Particles Using Multitrack Displaced Vertices Or Displaced Lepton Pairs in [math Display
Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one long-lived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. In this study, this analysis uses a data sample of proton-proton collisions at \(\sqrt{s} = 8\) TeV corresponding to an integrated luminosity of 20.3 fb−1 collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving R-parity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual long-lived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios.
Search for Type-III Seesaw Heavy Leptons in Leptonic Final States in Pp Collisions at [square Root]s
Abstract: A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139fb−1 of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on final states with three or four electrons or muons from the possible decays of new heavy leptons via intermediate electroweak bosons. No significant deviations above the Standard Model expectation are observed; upper and lower limits on the heavy lepton production cross-section and masses are derived respectively. These results are then combined for the first time with the ones already published by ATLAS using the channel with two leptons in the final state. The observed lower limit on the mass of the type-III seesaw heavy leptons combining two, three and four lepton channels together is 910 GeV at the 95% confidence level