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 by 10 cm triple-GEM detector scanned with a strongly collimated X-ray gun on a 2D motorized stage. Angular resolutions of60-84 urad 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 um.
A 1-meter-long trapezoidal Triple-GEM detector with wide readout strips was tested in hadron beams at the Fermilab Test Beam Facility in October 2013. The readout strips have a special zigzag geometry and run along the radial direction with an azimuthal pitch of 1.37 mrad to measure the azimuthal phi-coordinate of incident particles. The zigzag geometry of the readout reduces the required number of electronic channels by a factor of three compared to conventional straight readout strips while preserving good angular resolution. The average crosstalk between zigzag strips is measured to be an acceptable 5.5%. The detection efficiency of the detector is (98.4+-0.2)%. When the non-linearity of the zigzag-strip response is corrected with track information, the angular resolution is measured to be (193+-3) urad, which corresponds to 14% of the angular strip pitch. Multiple Coulomb scattering effects are fully taken into account in the data analysis with the help of a stand-alone Geant4 simulation that estimates interpolated track errors.
For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1 T solenoidal field and read out with three independent GEM-based readout modules, are reported. The TPC was exposed to a 6 GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.
Optical readout of GEM based devices by means of high granularity and low noise CMOS sensors allows to obtain very interesting tracking performance. Space resolution of the order of tens of $mu$m were measured on the GEM plane along with an energy resolution of 20%$div$30%. The main limitation of CMOS sensors is represented by their poor information about time structure of the event. In this paper, the use of a concurrent light readout by means of a suitable photomultiplier and the acquisition of the electric signal induced on the GEM electrode are exploited to provide the necessary timing informations. The analysis of the PMT waveform allows a 3D reconstruction of each single clusters with a resolution on z of 100 $mu$m. Moreover, from the PMT signals it is possible to obtain a fast reconstruction of the energy released within the detector with a resolution of the order of 25% even in the tens of keV range useful, for example, for triggering purpose.
A combination Time Projection Chamber-Cherenkov prototype detector has been developed as part of the Detector R&D Program for a future Electron Ion Collider. The prototype was tested at the Fermilab test beam facility to provide a proof of principle to demonstrate that the detector is able to measure particle tracks and provide particle identification information within a common detector volume. The TPC portion consists of a 10x10x10cm3 field cage, which delivers charge from tracks to a 10x10cm2 quadruple GEM readout. Tracks are reconstructed by interpolating the hit position of clusters on an array of 2x10mm2 zigzag pads The Cherenkov component consists of a 10x10cm2 readout plane segmented into 3x3 square pads, also coupled to a quadruple GEM. As tracks pass though the drift volume of the TPC, the generated Cherenkov light is able to escape through sparsely arranged wires making up one side of the field cage, facing the CsI photocathode of the Cherenkov detector. The Cherenkov detector is thus operated in a windowless, proximity focused configuration for high efficiency. Pure CF4 is used as the working gas for both detector components, mainly due to its transparency into the deep UV, as well as its high N0. Results from the beam test, as well as results on its particle id capabilities will be discussed.
The performance and long term stability of an optically readout Time Projection Chamber with an electron amplification structure based on three Gas Electron Multipliers was studied. He/CF$_4$ based gas mixtures were used in two different proportions (60/40 and 70/30) in a CYGNO prototype with 7 litres sensitive volume. With electrical configurations providing very similar electron gains, an almost full detection efficiency in the whole detector volume was found with both mixtures, while a light yield about 20% larger for the 60/40 was found. The electrostatic stability was tested by monitoring voltages and currents during 25 days. The detector worked in very stable and safe condition for the whole period. In the presence of less CF$_4$, a larger probability of unstable events was clearly detected.