A GEM readout with radial zigzag strips and linear charge-sharing response

Abstract

We study the position sensitivity of radial zigzag strips intended to read out large GEM detectors for tracking at future experiments. Zigzag strips can cover a readout area with fewer strips than regular straight strips while maintaining good spatial resolution. Consequently, they can reduce the number of required electronic channels and related cost for large-area GEM detector systems. A non-linear relation between incident particle position and hit position measured from charge sharing among zigzag strips was observed in a previous study. We significantly reduce this non-linearity by improving the interleaving of adjacent physical zigzag strips. Zigzag readout structures are implemented on PCBs and on a flexible foil and are tested using a 10 cm × 10 cm triple-GEM detector scanned with a strongly collimated X-ray gun on a 2D motorized stage. Angular resolutions of 60-84 µrad are achieved with a 1.37 mrad angular strip pitch at a radius of 784 mm. On a linear scale this corresponds to resolutions below 100 µm.

Design Studies for a TPC Readout Plane Using Zigzag Patterns With Multistage GEM Detectors

“…It should be noted that there have also been preliminary attempts to compensate for the manufacturing distortions described above by implementing design features like overstretched zigzags (cf. [5]). However, such techniques have had limited success, likely because identifying the optimal compensating design requires a dedicated effort beyond what was initially tried.…”

“…However, the width is estimated to be about 40-50microns (cf. [5]), which is a significant contributor to the quoted values of resolution and should in principle be reduced by this amount subtracted in quadrature. Nevertheless, the quoted resolution from the x-ray scans are only considered relative metrics, so it is not imperative to remove a constant term that is common to all measurements.…”

“…A comparison of the performance of these two readout schemes, for a particular rectangular strip geometry and a less than optimal zigzag pattern is given in [1]. Additional studies of zigzag and chevron pad structures are given in [2], [3], [4], and [5]. Fig.…”

A Low-mass GEM Detector with Radial Zigzag Readout Strips for Forward Tracking at the EIC

“…The resolution obtainable with such zigzag-strip structures is measured with a highly collimated X-ray source impinging on small Triple-GEM detectors equipped with 10 cm × 10 cm test boards that feature radial zigzag strips with close-tooptimal interleaving of adjacent strips on PCBs and on a foil [5]. We observe robust charge sharing among adjacent strips, which in turn results in a fully linear spatial response.…”

“…We observe robust charge sharing among adjacent strips, which in turn results in a fully linear spatial response. On a linear scale, strip pitches are around 1 mm and the zigzag readouts achieve linear spatial resolutions of 50-90 µm at medium gas gains around 3000 [5].…”