Search for long-lived particles decaying in the CMS endcap muon detectors in proton-proton collisions at $\sqrt{s} = $ 13 TeV

TL;DR

This paper reports a search for long-lived particles produced from Higgs boson decays using CMS detector data, employing a novel reconstruction technique, setting new limits on Higgs to LLP decay branching fractions for certain mass and decay length ranges.

Contribution

It introduces a new method to reconstruct LLP decays in the CMS endcap muon detectors and provides the most stringent limits to date on Higgs to LLP branching fractions for specific decay lengths and masses.

Findings

No excess events observed above background.

Set new upper limits on Higgs to LLP decay branching fractions.

Sensitive to LLP masses as low as a few GeV and decay lengths over 6 meters.

Abstract

A search for long-lived particles (LLPs) produced in decays of standard model (SM) Higgs bosons is presented. The data sample consists of 137 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 13 TeV, recorded at the LHC in 2016-2018. A novel technique is employed to reconstruct decays of LLPs in the endcap muon detectors. The search is sensitive to a broad range of LLP decay modes and to masses as low as a few GeV. No excess of events above the SM background is observed. The most stringent limits to date on the branching fraction of the Higgs boson to LLPs subsequently decaying to quarks and $\tau^+\tau^-$ are found for proper decay lengths greater than 6, 20, and 40 m, for LLP masses of 7, 15, and 40 GeV, respectively.