Absolute Position Measurement in a Gas Time Projection Chamber via Transverse Diffusion of Drift Charge

TL;DR

This paper demonstrates a novel method to measure the absolute position of tracks in a gas TPC by analyzing transverse diffusion of drift charge, achieving centimeter-level precision without needing initial ionization details.

Contribution

It introduces a new technique for absolute position measurement in gas TPCs using transverse diffusion analysis, not previously demonstrated in such detectors.

Findings

Achieved 1 cm precision for 1 cm alpha track segments.

First demonstration of absolute position measurement via transverse diffusion in a gas TPC.

Method is robust against charge density saturation and does not require initial ionization knowledge.

Abstract

Time Projection Chambers (TPCs) with charge readout via micro pattern gaseous detectors can provide detailed measurements of charge density distributions. We here report on measurements of alpha particle tracks, using a TPC where the drift charge is amplified with Gas Electron Multipliers and detected with a pixel ASIC. We find that by measuring the 3-D topology of drift charge and fitting for its transverse diffusion, we obtain the absolute position of tracks in the drift direction. For example, we obtain a precision of 1~cm for 1~cm-long alpha track segments. To our knowledge this is the first demonstration of such a measurement in a gas TPC. This technique has several attractive features: it does not require knowledge of the initial specific ionization, is robust against bias from diffuse charge below detection threshold, and is also robust against high charge densities that saturate the detector response.