Search for metastable heavy charged particles with large ionisation energy loss in $pp$ collisions at $\sqrt{s}$ = 8 TeV using the ATLAS experiment

TL;DR

This paper reports a search for metastable heavy charged particles with large ionisation energy loss in 8 TeV proton-proton collisions using the ATLAS detector, setting new mass and lifetime limits on such particles.

Contribution

It introduces a novel search method for long-lived charged particles based on their ionisation energy loss and track parameters in the ATLAS detector.

Findings

No significant deviation from the Standard Model was observed.

Gluino R-hadrons with 10 ns lifetime and masses up to 1185 GeV are excluded.

Charginos with 15 ns lifetime and masses up to 482 GeV are excluded.

Abstract

Many extensions of the Standard Model predict the existence of charged heavy long-lived particles, such as $R$-hadrons or charginos. These particles, if produced at the Large Hadron Collider, should be moving non-relativistically and are therefore identifiable through the measurement of an anomalously large specific energy loss in the ATLAS pixel detector. Measuring heavy long-lived particles through their track parameters in the vicinity of the interaction vertex provides sensitivity to metastable particles with lifetimes from 0.6 ns to 30 ns. A search for such particles with the ATLAS detector at the Large Hadron Collider is presented, based on a data sample corresponding to an integrated luminosity of 18.4 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 8 TeV. No significant deviation from the Standard Model background expectation is observed, and lifetime-dependent upper limits on $R$-hadrons and chargino production are set. Gluino $R$-hadrons with 10 ns lifetime and masses up to 1185 GeV are excluded at 95$\%$ confidence level, and so are charginos with 15 ns lifetime and masses up to 482 GeV.