Search for soft unclustered energy patterns containing muons in the final state in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

TL;DR

This paper reports a search for soft unclustered energy patterns with muons in proton-proton collisions at 13 TeV using ATLAS data, setting limits on hidden sector models without observing a significant excess.

Contribution

First search for SUEPs with muons in the final state at the LHC, providing new exclusion limits on hidden valley scenarios with scalar mediators.

Findings

No significant excess over Standard Model expectations.

Set exclusion limits on mediator production cross section and decay branching fractions.

Limits reach as low as 0.05 fb for certain mediator masses.

Abstract

Soft unclustered energy patterns (SUEPs) refer to high-multiplicity, isotropic distributions of low-momentum particles that could arise in strongly-coupled hidden sector theories. A search for SUEPs whose decay products contain muons in the final state is presented using 140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$ = 13 TeV collected by the ATLAS detector at the Large Hadron Collider during 2015-2018. The analysis targets SUEP signatures via gluon-gluon fusion production of a scalar mediator in Hidden Valley scenarios. No significant excess over the Standard Model expectation is observed. Exclusion limits are set on the product of the mediator production cross section and the branching fraction for its decay into a SUEP, down to 0.05 fb for a mediator mass of $m_S$ = 750 GeV, 0.4 fb for $m_S$ = 400 GeV, and 70 fb for $m_S$ = 125 GeV; the last value, when identifying the mediator with the Standard Model Higgs boson, translates to an upper limit on the branching fraction of around 0.2%.