G. Croci

Development of THGEM-based photon detectors for Cherenkov Imaging Counters

The development of a large size gaseous detector of single photons, able to stably operate at high gain and high rate, and to provide good time resolution and insensitivity to magnetic field would be beneficial to future Cherenkov Imaging Counters. The detector could be based on the use of a multilayer architecture of THGEM electron multipliers coupled to a solid state CsI photocathode. A systematic study of the response of THGEM-based counters versus the geometrical parameters has been performed and the main results will be presented. Small photon detector prototypes have been built and preliminary data obtained detecting single photoelectrons are presented as well. The key aspect of photoelectron extraction from the photocathode is illustrated presenting both simulation and dedicated measurement results.

Characterization of GEM detectors for application in the CMS muon detection system

The muon detection system of the Compact Muon Solenoid experiment at the CERN Large Hadron Collider is based on different technologies for muon tracking and triggering. In particular, the muon system in the endcap disks of the detector consists of Resistive Plate Chambers for triggering and Cathode Strip Chambers for tracking. At present, the endcap muon system is only partially instrumented with the very forward detector region remaining uncovered. In view of a possible future extension of the muon endcap system, we report on a feasibility study on the use of Micro-Pattern Gas Detectors, in particular Gas Electron Multipliers, for both muon triggering and tracking. Results on the construction and characterization of small triple-Gas Electron Multiplier prototype detectors are presented.

Progress on large area GEMs

In 2008, a triple GEM detector prototype with an area of ~ 2000 cm2 has been constructed, based on foils of 66 × 66 cm. GEMs of such dimensions had not been made before, and innovations to the existing technology were introduced to build this detector. This paper discusses these innovations and presents further work on large area GEM development. A single-mask technique overcomes the cumbersome practice of alignment of two masks, which limits the achievable lateral size. The holes obtained with this technique are conical, and have a so-called rim, a small insulating clearance around the hole in the substrate. Further refinements of this technique allow greater control over the shape of holes and the size of rims. Also, an improvement in homogeneity over large areas is expected. Simulation studies have been done to examine the effect of hole shape on the behavior of GEMs. Such studies can help understanding how to use new enhancements of the technique to optimize performance. Many potential applications for large area GEMs foresee large production volumes. Production issues have been studied, and single-mask GEMs turn out to be much more suitable for large scale production than standard GEMs.

Micropattern gaseous photon detectors for Cherenkov imaging counters

RICH counters for PID in the high momentum domain and in large acceptance experiments require photon detectors covering extended surface of several square meters and able to accept Cherenkov photons in a wide angular range. An ideal approach is represented by gaseous photon detectors, which allow covering wide surfaces at affordable costs.

Construction of the first full-size GEM-based prototype for the CMS high-η muon system

In view of a possible extension of the forward CMS muon detector system and future LHC luminosity upgrades, Micro-Pattern Gas Detectors (MPGDs) are an appealing technology. They can simultaneously provide precision tracking and fast trigger information, as well as sufficiently fine segmentation to cope with high particle rates in the high-eta region at LHC and its future upgrades. We report on the design and construction of a full-size prototype for the CMS endcap system, the largest Triple-GEM detector built to-date. We present details on the 3D modeling of the detector geometry, the implementation of the readout strips and electronics, and the detector assembly procedure.

A large area GEM detector

A prototype triple gem detector has been constructed with an area of ∼2000 cm2, based on foils of 66 cm × 66 cm. GEMS of such dimensions have not been made before, and innovations to the existing technology were made to build this detector.

Making spherical GEMs

We developed a method to make GEM foils with a spherical geometry. Tests of this procedure and with the resulting spherical GEMs are presented. Together with a spherical drift electrode, a spherical conversion gap for x-rays can be formed. This would eliminate the parallax error in an x-ray diffraction setup, which limits the spatial resolution at wide diffraction angles. The method is inexpensive and flexible towards possible changes in the design. We show advanced plans to make a prototype of an entirely spherical triple-GEM detector, including a spherical readout structure. This detector will have a superior position resolution, also at wide diffraction angles, and a high rate capability. A completely spherical gaseous detector has never been made before.

Spherical gems for parallax-free detectors

We developed a method to make gem foils with a spherical geometry. Tests of this procedure and with the resulting spherical gems are presented. Together with a spherical drift electrode, a spherical conversion gap can be formed. This would eliminate the parallax error for detection of x-rays, neutrons or uv photons when a gaseous converter is used. This parallax error limits the spatial resolution at wide scattering angles. The method is inexpensive and flexible towards possible changes in the design. We show advanced plans to make a prototype of an entirely spherical triple-gem detector, including a spherical readout structure. This detector will have a superior position resolution, also at wide angles, and a high rate capability. A completely spherical gaseous detector has never been made before.

An overview of the design, construction and performance of large area triple-GEM prototypes for future upgrades of the CMS forward muon system

GEM detectors are used in high energy physics experiments given their good spatial resolution, high rate capability and radiation hardness. An international collaboration is investigating the possibility of covering the 1.6 < |?| < 2.4 region of the CMS muon endcaps with large-area triple-GEM detectors. The CMS high-? area is actually not fully instrumented, only Cathode Strip Chamber (CSC) are installed. The vacant area presents an opportunity for a detector technology able to to cope with the harsh radiation environment; these micropattern gas detectors are an appealing option to simultaneously enhance muon tracking and triggering capabilities in a future upgrade of the CMS detector. A general overview of this feasibility study is presented. Design and construction of small (10cm ? 10cm) and full-size trapezoidal (1m ? 0.5m) triple-GEM prototypes is described. Results from measurements with x-rays and from test beam campaigns at the CERN SPS is shown for the small and large prototypes. Preliminary simulation studies on the expected muon reconstruction and trigger performances of this proposed upgraded muon system are reported.

First results of spherical GEMS

We developed a method to make gem foils with a spherical geometry. Tests of this procedure and with the resulting spherical gems are presented. Together with a spherical drift electrode, a spherical conversion gap can be formed. This eliminates the parallax error for detection of x-rays, neutrons or uv photons when a gaseous converter is used. This parallax error limits the spatial resolution at wide scattering angles. Besides spherical gems, we have developed curved spacers to maintain accurate spacing, and a conical field cage to prevent edge distortion of the radial drift field up to the limit of the angular acceptance of the detector. With these components first tests are done in a setup with a spherical entrance window but a planar readout structure; results will be presented and discussed. A flat readout structure poses difficulties, however. Therefore we will show advanced plans to make a prototype of an entirely spherical double-gem detector, including a spherical 2d readout structure. This detector will have a superior position resolution, also at wide angles, and a high rate capability.