M. Villa

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.

Beam test results for new full-scale GEM prototypes for a future upgrade of the CMS high-η Muon System

The CMS GEM collaboration is considering Gas Electron Multipliers (GEMs) for upgrading the CMS forward muon system in the 1.5 <; |η| <; 2.4 endcap region. GEM detectors can provide precision tracking and fast trigger information. They would improve the CMS muon trigger and muon momentum resolution and provide missing redundancy in the high-η region. Employing a new faster construction and assembly technique, we built four full-scale Triple-GEM muon detectors for the inner ring of the first muon endcap station. We plan to install these or further improved versions in CMS during the first long LHC shutdown in 2013/14 for continued testing. These detectors are designed for the stringent rate and resolution requirements in the increasingly hostile environments expected at CMS after the second long LHC shutdown in 2018/19. The new prototypes were studied in muon/pion beams at the CERN SPS. We discuss our experience with constructing the new full-scale production prototypes and present preliminary performance results from the beam test. We also tested smaller Triple-GEM prototypes with zigzag readout strips with 2 mm pitch in these beams and measured a spatial resolution of 73 μm. This readout offers a potential reduction of channel count and consequently electronics cost for this system while maintaining high spatial resolution.

Construction and performance of large-area triple-GEM prototypes for future upgrades of the CMS forward muon system

At present, part of the forward RPC muon system of the CMS detector at the CERN LHC remains uninstrumented in the high-η region. An international collaboration is investigating the possibility of covering the 1.6 &#60; |η| &#60; 2.4 region of the muon endcaps with large-area triple-GEM detectors. Given their good spatial resolution, high rate capability, and radiation hardness, these micro-pattern gas detectors are an appealing option for simultaneously enhancing muon tracking and triggering capabilities in a future upgrade of the CMS detector. A general overview of this feasibility study will be presented. The design and construction of small (10×10 cm2) and full-size trapezoidal (1 × 0.5 m2) triple-GEM prototypes will be described. During detector assembly, different techniques for stretching the GEM foils were tested. Results from measurements with x-rays and from test beam campaigns at the CERN SPS will be shown for the small and large prototypes. Preliminary simulation studies on the expected muon reconstruction and trigger performances of this proposed upgraded muon system will be reported.

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.

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.

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.

Analysis and correction of the magnetic field effects in the Hybrid Photo-Detectors of the RICH2 Ring Imaging Cherenkov detector of LHCb.

The Ring Imaging Cherenkov detectors of the LHCb experiment at the Large Hadron Collider at CERN are equipped with Hybrid Photo-Detectors. These vacuum photo-detectors are affected by the stray magnetic field of the LHCb magnet, which degrades their imaging properties. This effect increases the error on the Cherenkov angle measurement and would reduce the particle identification capabilities of LHCb. A system has been developed for the RICH2 Ring Imaging Cherenkov detector to perform a detailed characterisation of the magnetic distortion effects. It is described, along with the methods implemented to correct for these effects, restoring the optimal resolution.

Gas Electron Multiplier (GEM) application for Time Projection Chamber (TPC) gating

A voltage-controlled Gas Electron Multiplier (GEM) can be used to block the re-injection of positive ions in large volume Time Projection Chambers (TPC). Through an accurate choice of proper geometry, gas filling and external fields it is possible to obtain a sufficient level of electron transmission at very low GEM voltages (Gating GEM) despite the degradation of energy resolution due to the loss of primary electrons. The addition of a pre-amplification GEM in front of the Gating GEM causes an improvement in energy resolution while keeping the ion feedback at the level of primary ionization. The measurements show that a small pulse of about 40 V completely closes the gate, stopping the ions produced in the amplification stage.

Test beam results of the GE1/1 prototype for a future upgrade of the CMS high-η muon system

Gas Electron Multipliers (GEM) are an interesting technology under consideration for the future upgrade of the forward region of the CMS muon system, specifically in the 1.6 &#60; ∣η∣ &#60; 2:4 endcap region. With a sufficiently fine segmentation GEMs can provide precision tracking as well as fast trigger information. The main objective is to contribute to the improvement of the CMS muon trigger. The construction of large-area GEM detectors is challenging both from the technological and production aspects. In view of the CMS upgrade we have designed and built the largest full-size Triple-GEM muon detector, which is able to meet the stringent requirements given the hostile environment at the high-luminosity LHC. Measurements were performed during several test beam campaigns at the CERN SPS in 2010 and 2011. The main issues under study are efficiency, spatial resolution and timing performance with different inter-electrode gap configurations and gas mixtures. In this paper results of the performance of the prototypes at the beam tests will be discussed.

High-Efficiency Digital Readout Systems for Fast Pixel-based Vertex Detectors

Particle physics is one of the science branches which heavily relies on most advanced technologies due to the increasing complexity of the problems it has to face. In future colliders, luminosities and beam energies are scaling upwards. These are necessary conditions for the discovery of new physics which both result in a larger amount of data that need to be brought out of the detector. That’s why one of the crucial points for new experiments is the evolution of data acquisition systems. Data acquisition systems employed in particle physics experiments followed the global technology trend and moved towards digital electronics and transmission lines, in this chapter we will describe how the effort of our work has been applied in this direction trying to extend digital processing on the very front-end of the detector. We will show how digital elaboration on the very front-end can help coping with new stringent requirements. One possible scenario for the discovery of new physics is the chance to investigate with high-precision some apparently known processes instead of brutally scaling the s energy foreseeing to achieve the threshold for new heavy particle discovery. High luminosity ee accelerators can provide clean signals at very fast rates in order to provide in a reasonable amount of time the required statistics for high-precision new physics investigations. The next-generation flavour factories are aiming at luminosities up to 10cms (refer to SuperB Collaboration (2007)) which imply a very high particle rate especially in the first layer of the innermost detector: the vertex tracker. This perspective opened new challenging researches for the realization of very fast and efficient sensors and readout electronics capable to take advantage of these super-luminous facilities. In this chapter we would like to present our works on data acquisition chains, which is focused on the front-end side of the detector but involves also external DAQ boards. We will show how we have expanded digital signal processing of a classical DAQ systems outside the walls of the counting rooms to the front-end chips. What we present is far from being a complete and definitive DAQ for a tracker design, but it provides viable solutions and technicalities for what concern the readout electronics world. The front-ends targeted by our data acquisition system are silicon sensors and, in particular, wide matrices of pixels. The huge improvements of the last decade in the world of the silicon industries, and the new technology processes that emerged recently, have stimulated the curiosity of the scientific community. Several types of pixel sensors for particle physics