A search for long-lived, charged particles using ionization energy loss measurements from the ATLAS Muon Spectrometer with pp collision data at √s = 13 and 13.6 TeV

Abstract

All charged particles lose energy via ionization as they traverse detector material. For heavy particles, the amount of energy lost to ionization scales with $\beta\gamma$, and particles of different masses at the same momentum will deposit energy at measurably different rates. This feature is used to search for new, heavy, long-lived charged particles by combining an ionization energy loss (dE/dx) measurement with a momentum measurement to directly measure particle mass via the relation $m = p / \beta\gamma$. A complementary mass measurement for the same track, which improves background rejection, can be extracted using a measurement of particle speed $\beta$. The results from a search using dE/dx and $\beta$ measurements from the ATLAS Muon Spectrometer are presented. Events are required to have a high-momentum track in the Muon Spectrometer that is slowly moving compared to Standard Model particles at the same momentum. The development and calibration of the Muon Spectrometer dE/dx measurement, used for the first time in the search presented, is described. This search uses 140 fb$^{-1}$ of data collected at $\sqrt{s}=13$~TeV and 166.9 fb$^{-1}$ collected at $\sqrt{s} = 13.6$~TeV, and the results are interpreted in the context of a Supersymmetric model which predicts the existence of long-lived stau sleptons.