Gas detector development is one of the pillars of the research in fundamental physics. Since several years, a new concept of detectors, called Micro Pattern Gas Detector (MPGD), allowed to overcome ...several problems related to other types of commonly used detectors, like drift chamber and micro strips detectors, reducing the rate of discharges and providing better radiation tolerance. Among the most used MPGDs are the Gas Electron Multipliers (GEMs). Invented by Sauli in 1997, nowadays GEMs have become an important reality for particle detectors in high energy physics. Commonly deployed as fast timing detectors and triggers, their fast response, high rate capability and high radiation hardness make them also suitable as tracking detectors. The readout scheme is one of the most important features in tracking technology. Analog readout based on the calculation of the center of gravity technique allows to overcome the limit imposed by digital pads, whose spatial resolution is limited by the pitch dimensions. However, the presence of high external magnetic fields can distort the electronic cloud and affect the performance. The development of the micro-TPC reconstruction method brings GEM detectors into a new prospective, improving significantly the spatial resolutionin presence of high magnetic fields. This innovative technique allows to reconstruct the 3-dimensional particle position, as Time Projection Chamber, but within a drift gap of a few millimeters. In these report, the charge centroid and micro-TPC methods are described in details. We discuss the results of several test beams performed with planar chambers in magnetic field. These results are one of the first developments of micro-TPC technique for GEM detectors, which allows to reach unprecedented performance in a high magnetic field of 1 T.
A Monte Carlo triple-GEM simulation tuned with data Cossio, F.; Alexeev, M.; Amoroso, A. ...
2018 IEEE Nuclear Science Symposium and Medical Imaging Conference Proceedings (NSS/MIC),
2018-Nov.
Conference Proceeding
Triple-GEM detectors are a well known technology used in high energy physics experiments. A reliable Monte Carlo simulation has to be developed to reproduce the performance which have been measured ...experimentally, for example in beam tests, and be able to infer the future behavior in real conditions. In detail, the software has to simulate the response of the detector to the passage of particles, from the primary ionization, to the amplification and diffusion of the electrons and eventually to the induction of the charge on the anode strips. In the case of gas detectors, existing softwares such as GARFIELD++ already perform a very detailed simulation of the physical processes but are CPU time consuming. In this presentation a description of a faster simulation is presented. It models the results about the electron production (primary ionization and avalanche) and diffusion in a triple-GEM obtained from GARFIELD++ and then it reconstructs the signal induced on each anode strip according to the Shockley-Ramo theorem. The simulation has been tuned on the data collected in several beam tests and it can reproduce the real values of time and charge measured by the strip. When the reconstruction algorithms used in the field of Micro Pattern Gas Detectors, such as the Charge Centroid or the micro-Time Projection Chamber readout, are applied on the simulated data, the model shows performance comparable to the experimental one. This provides a validation of this model and allows to extend its usage in different conditions, i.e. geometries, presence of magnetic field, high voltage settings, different direction of the incident particles, to evaluate the expected outcome of the triple-GEM in those cases.
Gas detectors are very light instruments used in high energy physics to measure the particle properties: position and momentum. Gas Electron Multiplier (GEM) technology has been invented by F. Sauli ...in 1997 and in the past tens of years the knowledge of this Micro Pattern Gas Detector (MPGD) increased. A design with a triple-GEM has been used in several experiments in high energy physics such as TOTEM and COMPASS. This technology allows to achieve good spatial resolution performances and can be used to create large area detector with a shapeable surface, e.g. the KLOE2 Inner Tracker or the upcoming upgrade of the BESIII Inner Tracker. A triple-GEM uses three stages of GEMs, with high electric field, to amplify the number of the electrons produced by the primary ionization of the charged particle passing in the gas, with a total gain of about 10 4 . The signal is then collected on a segmented anode and dedicated algorithms are used to reconstruct the charged particle position. The measurement of both the time and the charge information on the anode strip allows to use two algorithms: the Charge Centroid and the micro-Time Projection Chamber readout. The CC is strongly performing with orthogonal tracks while the µTPC gives its best results if magnetic field or if non-orthogonal tracks are present. These reconstruction methods are anti-correlated and the combination of the two is needed to keep the spatial resolution stable between the regions with different performances. A beam test with planar triple-GEM has been performed and in this presentation the merging algorithm of the CC and µTPC as a function of the charge and the multiplicity of the signal will be shown: a stable spatial resolution of about 130 µm has been achieved. In addition to this, the impact of the transversal and longitudinal diffusions on the reconstruction in µTPC mode will be shown, as well as the inter-strip capacitance effect.
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