Abstract
A search for long-lived particles decaying into hadrons and at least one muon is presented. The analysis selects events that pass a muon or missing-transverse-momentum trigger and contain a displaced muon track and a displaced vertex. The analyzed dataset of proton-proton collisions at s=13 TeV was collected with the ATLAS detector and corresponds to 136 fb−1. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particle decays that occur in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are presented as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and interpreted as exclusion limits in scenarios with pair production of long-lived top squarks that decay via a small R-parity-violating coupling into a quark and a muon. Top squarks with masses up to 1.7 TeV are excluded for a lifetime of 0.1 ns, and masses below 1.3 TeV are excluded for lifetimes between 0.01 ns and 30 ns.1 MoreReceived 27 March 2020Accepted 1 July 2020DOI:https://doi.org/10.1103/PhysRevD.102.032006Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2020 CERN, for the ATLAS CollaborationPhysics Subject Headings (PhySH)Research AreasSupersymmetric modelsParticles & Fields
Highlights
The Standard Model (SM) of particle physics has successfully predicted the results of decades of laboratory experiments with impressive precision, but it suffers from several notable inadequacies
This paper reports a search for decays of long-lived particles (LLPs) including a muon, using the full Run-2 dataset of the ATLAS experiment
As the probability of passing or failing the muon veto does not depend on the displaced vertices (DVs) properties of the event, this transfer factor can be measured in the DV control region (CR) and applied in the DV Signal Region (DV SR) in order to estimate the background contribution
Summary
The Standard Model (SM) of particle physics has successfully predicted the results of decades of laboratory experiments with impressive precision, but it suffers from several notable inadequacies. Many of these constraints suggest that the value of any nonzero RPV coupling needs to be small This naturally leads to suppression of the decay processes and can give rise to long-lived SUSY particles. In models with sufficiently small λ023k coupling values and where thet squark is the LSP, the suppression of the decay causes it to occur at discernible distances from the pp interaction point where thet squark pair was produced This would give rise to muons and high-mass vertices that are significantly displaced from the interaction point, yielding a distinctive detector signature in a collider experiment, with no irreducible backgrounds from SM processes. The predictions of the background yields are entirely derived in data, with individual contributions estimated from dedicated control regions
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