Resolution studies of cosmic-ray tracks in a TPC with GEM readout

Abstract

A large volume TPC is a leading candidate for the central tracking detector at a future high energy linear collider. To improve the resolution a new readout based on micro-pattern gas detectors is being developed. Measurements of the spatial resolution of cosmic-ray tracks in a GEM TPC are presented. We find that the resolution suffers if the readout pads are too wide with respect to the charge distribution at the readout plane due to insufficient charge sharing. For narrow pads of 2 × 6 mm 2 we measure a resolution of 100 µm at short drift distances in the absence of an axial magnetic field. The dependence of the spatial resolution as a function of drift distance allows the determination of the underlying electron statistics. Our results show that the present technique uses about half the statistical power available from the number of primary electrons. The track angle effect is observed as expected.

Ion feedback suppression in time projection chambers

“…It should be noted that the authors of Ref. [7], operating a standard triple-GEM detector, reported a two-fold increase of the anode current from zero to five tesla; exploiting the results of a GARFIELD simulation [29], this was explained as being due to an increase of the extraction drift lines 3 . In our understanding, the increase is due instead to the reduction of transverse diffusion losses; the reduction in positive ion feedback (also by a factor of two) is then in fact due to the increase in the electron signal at the anode.…”

“…In both cases, the time zero reference could be obtained with a separate 2 In the ternary mixture, due to charge transfer collisions, only ions with the lowest ionization potential (CO 2 + ) are left drifting; their lower mobility(~1 cm 2 V -1 s -1 ) has to be taken into account for gating. 3 In the simulation, using the Runge-Kutta option, the transverse diffusion is neglected. fast detector in line with the beam.…”

“…Motivated by the requirements of the detectors under design for the International Linear Collider (ILC) [2], a large amount of work has been devoted recently to assess the operating performances of GEM-TPC tracking devices, in particular for operation in high magnetic fields [3][4][5][6][7][8][9][10]. A constant charge gain and a point accuracy around 100 µm rms have been demonstrated in prototype detectors operated in high magnetic fields [7].…”

Development of a time projection chamber using gas electron multipliers (GEM–TPC)

“…Ar(90%)-CH 4 (10%) is widely used in TPCs and GEMs [11,17,18]. A fast drift velocity that peaks at a low electric field of 130 V/cm is the primary attribute of Ar-CH 4 , and such a low electric field is an advantage for detector operation.…”

“…A GEM-TPC is a strong candidate to be a central tracking detector in high energy heavy ion collision experiments [7,8,9,10,11].…”