Observables for Recoil Identification in High-Definition Gas Time Projection Chambers

TL;DR

This paper introduces new observables based on ionization topology in high-definition gas TPCs that significantly improve the discrimination between electron and nuclear recoils at low energies, enhancing directional detection capabilities.

Contribution

It proposes novel observables for recoil identification in gas TPCs that outperform traditional methods by up to three orders of magnitude at keV energies.

Findings

New observables outperform dE/dx in recoil discrimination

Effective at ionization energies below 10 keV

Robust even when directional information is lost

Abstract

Directional detection of nuclear recoils is broadly desirable in nuclear and particle physics. At low recoil energies, this capability may be used to confirm the cosmological origin of a dark matter signal, to penetrate the so-called neutrino floor, or to distinguish between different neutrino sources. Gas Time Projection Chambers (TPCs) can enable directional recoil detection if the readout granularity is sufficiently high, as is the case when micro-pattern gaseous detectors (MPGDs) are utilized. A key challenge in such detectors is identifying and rejecting background electron recoil events caused by gamma rays from radioactive contaminants in the detector materials and the environment. We define new observables that can distinguish electron and nuclear recoils, even at keV-scale energies, based on the simulated ionization's topology. We perform a simulation study that shows these observables outperform the traditionally used discriminant, dE/dx, by up to three orders of magnitude. Furthermore, these new observables work well even at ionization energies well below 10 keV and remain robust even in the regime where directionality fails.