Speaker
Description
Gaseous detectors with highly segmented charge readout and single-electron detection efficiency near unity are of interest for low-energy rare-event detection. Traditionally, R&D has focused on nuclear recoils, while electron recoils in the 1-100 keV energy range are a dominant background for directional CEνNS and dark matter experiments.
Electron recoils, however, constitute part or all of the signal in several important applications, including Migdal-effect measurements, directional solar-neutrino measurements, and searches for neutrinoless double-beta decay and electron-scattering dark matter.
At these energies, strong multiple scattering produces complex electron-recoil topologies and fundamentally limits directional reconstruction. Standard heavy-particle multiple-scattering approximations are not expected to accurately describe this regime. Detector effects such as readout segmentation, inefficiency, dynamic range, charge integration time, and channel-reset times also impact the observed recoil topology.
We study these effects experimentally using 40 cm³ TPCs with double-GEM amplification and ATLAS FE-I4B pixel ASIC readout, operated in 70:30 He:CO₂ at atmospheric pressure. Using simple straight-line fits to 20-28 keV electron-recoil tracks, we obtain a preliminary planar angular resolution of approximately 22° RMS at the optimal fit length, consistent with simulation. We discuss the relative importance of detector performance for angular and energy resolution, and the implications for a 40 L TPC, now being commissioned, that aims to approach the fundamental limits of both.