Single-hit resolution measurement with MEG II drift chamber prototypes

TL;DR

This paper reports on measurements of single-hit resolution in helium-based drift chamber prototypes for the MEG II experiment, demonstrating a resolution of about 110 micrometers using various testing methods and sources.

Contribution

It provides the first direct measurement of single-hit resolution in helium-based MEG II drift chamber prototypes, validating previous indirect estimates.

Findings

Single-hit resolution measured at 110 μm

Consistent results across different prototypes and methods

Helium/isobutane mixtures suitable for high-resolution tracking

Abstract

Drift chambers operated with helium-based gas mixtures represent a common solution for tracking charged particles keeping the material budget in the sensitive volume to a minimum. The drawback of this solution is the worsening of the spatial resolution due to primary ionisation fluctuations, which is a limiting factor for high granularity drift chambers like the MEG II tracker. We report on the measurements performed on three different prototypes of the MEG II drift chamber aimed at determining the achievable single-hit resolution. The prototypes were operated with helium/isobutane gas mixtures and exposed to cosmic rays, electron beams and radioactive sources. Direct measurements of the single hit resolution performed with an external tracker returned a value of 110 $\mu$m, consistent with the values obtained with indirect measurements performed with the other prototypes.