Search for long-lived neutral particles produced in $pp$ collisions at $\sqrt{s} = 13$ TeV decaying into displaced hadronic jets in the ATLAS inner detector and muon spectrometer

TL;DR

This paper reports a search for long-lived neutral particles decaying into displaced hadronic jets in the ATLAS detector, setting new limits on scalar boson decays with lifetimes from 5 cm to 1 m.

Contribution

It introduces specialized techniques for reconstructing displaced tracks and vertices in the inner detector and muon spectrometer, extending previous limits on long-lived scalar particles.

Findings

One event observed, consistent with background

Limits set on scalar boson decays for masses 125-1000 GeV

Extended exclusion limits for proper lifetimes 5 cm to 1 m

Abstract

A search is presented for pair-production of long-lived neutral particles using 33 fb$^{-1}$ of $\sqrt{s} = 13$ TeV proton-proton collision data, collected during 2016 by the ATLAS detector at the LHC. This search focuses on a topology in which one long-lived particle decays in the ATLAS inner detector and the other decays in the muon spectrometer. Special techniques are employed to reconstruct the displaced tracks and vertices in the inner detector and in the muon spectrometer. One event is observed that passes the full event selection, which is consistent with the estimated background. Limits are placed on scalar boson propagators with masses from 125 GeV to 1000 GeV decaying into pairs of long-lived hidden-sector scalars with masses from 8 GeV to 400 GeV. The limits placed on several low-mass scalars extend previous exclusion limits in the range of proper lifetimes $c \tau$ from 5 cm to 1 m.