Search for dimuon resonance in the 35 to 75 GeV mass range using 140 fb$^{-1}$ of 13 TeV $pp$ collisions with the ATLAS detector

TL;DR

This paper reports a model-independent search for low-mass dimuon resonances between 35 and 75 GeV using 140 fb$^{-1}$ of 13 TeV proton-proton collision data from ATLAS, employing Gaussian process regression to model backgrounds.

Contribution

It introduces a novel background modeling technique using Gaussian process regression for low-mass resonance searches in the dimuon channel.

Findings

No significant excess observed in the mass range.

Sets upper limits on production cross-sections from 20 fb to 110 fb.

Provides new constraints on dark-photon and dark-matter-mediator models.

Abstract

A model-independent search for low-mass resonances decaying into pairs of oppositely charged muons is presented. The analysis uses proton-proton collision data corresponding to an integrated luminosity of 140 fb$^{-1}$, recorded by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. The search targets hypothetical dimuon resonances in the invariant mass range from 35 GeV to 75 GeV. The modelling of this mass region is particularly challenging for conventional analytic background parameterisations. To address this, a Gaussian process regression technique is used to model the background. The dimuon mass spectrum is analysed for potential signals, and no statistically significant excess is observed. Upper limits at the 95% confidence level are set on the fiducial production cross-section of new resonances decaying promptly into muons, ranging from 20 fb to 110 fb, depending on the resonance mass. These results are further interpreted in the context of dark-photon and dark-matter-mediator models, leading to new constraints on their parameter spaces.