Giovanni Mocellin

The high-luminosity phase of the Large Hadron Collider (HL-LHC) will result in ten times higher particle background than measured during the first phase of LHC operation. In order to fully exploit the highly-demanding operating conditions during HL-LHC, the Compact Muon Solenoid (CMS) Collaboration will use Gas Electron Multiplier (GEM) detector technology. The technology will be integrated into the innermost region of the forward muon spectrometer of CMS as an additional muon station called GE1∕1. The primary purpose of this auxiliary station is to help in muon reconstruction and to control level-1 muon trigger rates in the pseudo-rapidity region 1.6≤|η|≤2.2. The new station will contain trapezoidal-shaped GEM detectors called GE1∕1 chambers. The design of these chambers is finalized, and the installation is in progress during the Long Shutdown phase two (LS-2) that started in 2019. Several full-size prototypes were built and operated successfully in various test beams at CERN. We describe performance measurements such as gain, efficiency, and time resolution of these prototype chambers, developed after years of R&D, and summarize their behavior in different gas compositions as a function of the applied voltage.

After the Phase-2 high-luminosity upgrade to the Large Hadron Collider (LHC), the collision rate and therefore the background rate will significantly increase, particularly in the high $\eta$ region. To improve both the tracking and triggering of muons, the Compact Muon Solenoid (CMS) Collaboration plans to install triple-layer Gas Electron Multiplier (GEM) detectors in the CMS muon endcaps. Demonstrator GEM detectors were installed in CMS during 2017 to gain operational experience and perform a preliminary investigation of detector performance. We present the results of triple-GEM detector performance studies performed in situ during normal CMS and LHC operations in 2018. The distribution of cluster size and the efficiency to reconstruct high $p_T$ muons in proton--proton collisions are presented as well as the measurement of the environmental background rate to produce hits in the GEM detector.

Gas Electron Multiplier (GEM) technology, in particular triple-GEM, was selected for the upgrade of the CMS endcap muon system following several years of intense effort on R&D. The triple-GEM chambers (GE1/1) are being installed at station 1 during the second long shutdown with the goal of reducing the Level-1 muon trigger rate and improving the tracking performance in the harsh radiation environment foreseen in the future LHC operation [1]. A first installation of a demonstrator system started at the beginning of 2017: 10 triple-GEM detectors were installed in the CMS muon system with the aim of gaining operational experience and demonstrating the integration of the GE1/1 system into the trigger. In this context, a dedicated Detector Control System (DCS) has been developed, to control and monitor the detectors installed and integrating them into the CMS operation. This paper presents the slice test DCS, describing in detail the different parts of the system and their implementation.

Abstract The CMS experiment is one of the two general purpose experiments at the CERN LHC. During LHC Phase-2 starting from 2026, the instantaneous luminosity delivered to CMS will reach 5 × 10 34 cm −2 s −1 , resulting in high particle fluxes that require the detector to be upgraded. The forward regions, corresponding to the endcaps of the detectors, will be most affected. In the muon endcap system, triple-GEM chambers will complement the existing Cathode Strip Chambers, leading to a better identification of the muon tracks and a reduction of the trigger rate due to the suppression of fake candidates. Additionally, the forward coverage will be extended. GEM chambers are being built in production sites spread in 7 countries around the world for the first station of the muon endcaps. Each chamber has an area of approximately 1 m 2 . Thus, high requirements on the uniformity across the detector are needed and the GEM chambers undergo multiple quality control tests. In parallel with the production and testing of the chambers, 10 GEM chambers have been integrated in CMS and are currently under commissioning (slice test). Such a test is essential to prepare for the upcoming installation and integration. This contribution gives an introduction to GEM chambers and presents some results of the performance tests, both for quality control and slice test.

The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (∼ O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.

During the High Luminosity LHC, the Drift Tube chambers installed in the CMS detector need to operate with an integrated dose ten times higher than expected at the LHC due to the increase in integrated luminosity from 300 fb-1 to 3000 fb-1. Irradiations have been performed to assess the performance of the detector under such conditions and to characterize the radiation aging of the detector. The presented analysis focuses on the behaviour of the high voltage currents and the dose measurements needed to extrapolate the results to High Luminosity conditions, using data from the photon irradiation campaign at GIF++ in 2016 as well as the efficiency analysis from the irradiation campaign started in 2017. Although the single-wire loss of high voltage gain observed of 70% is very high, the muon reconstruction efficiency is expected to decrease less than 20% during the full duration of High Luminosity LHC in the areas under highest irradiation.

Gas electron multipliers (GEMs) belong to the most modern and advanced technologies in the field of gaseous detectors. Detectors, based on the GEM technology, enjoy great popularity in various fields of physics. Especially in the field of high-energy physics, GEMs are well-appreciated thanks to their flexibility in geometry, resistance to aging and excellent performance in high-rate environments. The core of the detector consists of thin foils with an etched pattern of holes. The detection principle relies on electron multiplication inside the holes, where a high electric field is present. New etching techniques have been used for the production of large-size (0.3 m2 - 0.4 m2) GEM foils needed for high-energy physics experiments. The new techniques result in different hole geometries. To better understand the gas gain dependence on the hole geometry, several measurements have been performed with a triple-GEM detector, and have been complemented by GARFIELD++ simulations. The results are compared with other recent studies.

Abstract A temperature monitoring system based on fibre Bragg grating (FBG) fibre optic sensors has been developed for the gas electron multiplier (GEM) chambers of the Compact Muon Solenoid (CMS) detector. The monitoring system was tested in prototype chambers undergoing a general test of the various technological solutions adopted for their construction. The test lasted about two years and was conducted with the chambers being installed in the CMS detector and operated during regular experimental running. In this paper, we present test results that address the choice of materials and procedures for the production and installation of the FBG temperature monitoring system in the final GEM chambers.

An estimate of environmental background hit rate on triple-GEM chambers is performed using Monte Carlo (MC) simulation and compared to data taken by test chambers installed in the CMS experiment (GE1/1) during Run-2 at the Large Hadron Collider (LHC). The hit rate is measured using data collected with proton-proton collisions at 13 TeV and a luminosity of 1.5$\times10^{34}$ cm$^{-2}$ s$^{-1}$. The simulation framework uses a combination of the FLUKA and Geant4 packages to obtain the hit rate. FLUKA provides the radiation environment around the GE1/1 chambers, which is comprised of the particle flux with momentum direction and energy spectra ranging from $10^{-11}$ to $10^{4}$ MeV for neutrons, $10^{-3}$ to $10^{4}$ MeV for $\gamma$'s, $10^{-2}$ to $10^{4}$ MeV for $e^{\pm}$, and $10^{-1}$ to $10^{4}$ MeV for charged hadrons. Geant4 provides an estimate of detector response (sensitivity) based on an accurate description of detector geometry, material composition and interaction of particles with the various detector layers. The MC simulated hit rate is estimated as a function of the perpendicular distance from the beam line and agrees with data within the assigned uncertainties of 10-14.5%. This simulation framework can be used to obtain a reliable estimate of background rates expected at the High Luminosity LHC.

Caratterizzazione di un rivelatore gamma a scintillazione di dimensioni 5x5x10 per il sistema di ispezione non distruttiva con neutroni veloci (TNIS), prototipo del progetto C-BORD, accoppiato ad un digitizer per la lettura dei segnali. Ne e stata verificata la linearita, sono state ottenute la risoluzione energetica e temporale e sono state studiate le caratteristiche in funzione del tempo di accensione dell'apparato. E stato, inoltre, caratterizzato un rivelatore Nal(TI) 3x3, comparandone le prestazioni a quello di dimensioni maggiori.

Particelle “Long Lived” sono contenute in molte teorie oltre il Modello Standard. Se la vita media e sufficientemente lunga, le particelle possono entrare nei rivelatori ed attraversarli prima di decadere. Una caratteristica specifica delle particelle pesanti, con masse dal centinaio di GeV a oltre il TeV, e il loro β<1 e la loro maggiore perdita di energia per ionizzazione. La tesi si inserisce nella ricerca dell’identificazione di tali particelle pesanti nell’esperimento CMS dell’acceleratore LHC del CERN. Nell’esperimento CMS la misura del s e ottenuta sia con la misura della ionizzazione nel rivelatore centrale che con la misura del tempo di volo nelle varie parti del sistema di rivelatori dei muoni. Poiche il sistema di identificazione delle interazioni con muoni, trigger dei µ di livello 1, si basa sulla sincronizzazione di tutto il rivelatore con particelle SM relativistiche, aventi s=1, per s<0.5 tale sistema di trigger risulta completamente inefficiente. Una parte della tesi e dedicata alla ricerca e alla definizione di un nuovo trigger di “muoni” a livello 1 con le camere DT efficiente anche per particelle a basso s, quali le HSCP, senza ridurre le prestazioni del trigger delle particelle a s=1. Esso prende in considerazione topologie temporali della traccia rivelata a varie distanze dal vertice per le quali si abbia grande probabilita di identificare HSCP. L’altro aspetto analizzato nella tesi e lo studio dell’invecchiamento delle camere a deriva (DT) che sono usate nell’esperimento CMS sia per la misura della deviazione delle tracce nel campo magnetico (e quindi nella misura del momento) che nella identificazione degli eventi con muoni (trigger di livello 1). Questo aspetto e di essenziale importanza in vista non solo della luminosita integrata nei prossimi anni di presa dati (2017 e 2018) ma soprattutto di HL-LHC; tale rivelatore DT era stato infatti disegnato e quindi costruito per funzionare ottimamente fino a una luminosita integrata pari a 1/10 di quella prevista al termine di HL-LHC. Per studiare le cause di tale invecchiamento sono stati progettati e costruiti rivelatori, denominati bicelle, con conformazione e materiali identici a quelli utilizzati per le camere DT di CMS, ma di dimensioni minori e caratteristiche tali da separare le possibili parti degassanti delle camere stesse (elettronica, chiusure, colle). Gli studi degli effetti della radiazione e quindi dell’invecchiamento di tali rivelatori ridotti sono in corso. Lo studio dei fenomeni di aging e quindi dell’efficienza dei rivelatori DT sono di importanza cruciale per conoscere il comportamento del rivelatore dei muoni. Inoltre, poiche la misura del s nelle ricerche di HSCP a HL-LHC si basera essenzialmente sulle misure temporali date dai rivelatori dei muoni, le previsioni di aging verranno utilizzate nello studio di tale canale HSCP a HL-LHC.

To sustain and extend its discovery potential, the Large Hadron Collider (LHC) will undergo a major upgrade in the coming years, referred to as High Luminosity LHC (HLLHC), aimed to increase its instantaneous luminosity, 5 times larger than the designed limit, and, consequently leading to high levels of radiation, with the goal to collect 10 times larger the original designed integrated luminosity. The drift tube chambers (DT) of CMS muon detector system is built to proficiently measure and trigger on muons in the harsh radiation environment expected during the HL-LHC era. Ageing studies are performed at the CERNs gamma ray irradiation facility (GIF++) by measuring the muon hit efficiency of these detectors at various LHC operation conditions. One such irradiation campaign was started in October 2017, when a spare MB2 chamber moved inside the bunker and irradiated at lower acceleration factors. Two out of twelve layers of the DT chamber were operated while being irradiated with the radioactive source and then their muon hit efficiency was calculated in coincidence with other ten layers which were kept on the standby. The chamber absorbed an integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway and strategies to mitigate the aging effects are also being developed. The effect of radiation on the performance of DT chamber and its impact on the overall muon reconstruction efficiency expected during the HL-LHC are presented.

The CMS Collaboration has been developing a Gas Electron Multiplier (GEM) detector in the endcap regions of the CMS muon system to maintain the high level of performance achieved during Run 2 in the challenging environment of the high-luminosity phase of the LHC (HL-LHC).The GEM detectors at endcap station 1 (GE1/1) were installed during the second long shutdown.The technical and operational challenges of large-area GEM detectors have been identified during the commissioning of five GEM super chambers ("slice test") in Run 2. This led to a modification in its system design.A test with cosmic-ray muons is the final stage of quality control before the full-scale installation into the CMS detector.We review the performance of muon detection in the slice test, an improvement of the readout system, commissioning status, and prospects for the muon trigger for Run 3.