Forward Muon System Research Articles

Improved Resistive Plate Chambers for Phase-II upgrade of the CMS detector in LHC

In anticipation of the High Luminosity LHC, an extensive upgrade is underway for the CMS Muon system to ensure its optimal performance in muon triggering and reconstruction. The indispensable role of Resistive Plate Chambers (RPC) as dedicated muon detectors stems from their exceptional timing resolution. To meet the requirements of Phase-II of the LHC, the RPC system will be expanded up to a pseudorapidity of 2.4. The forward Muon system’s upcoming RE3/1 and RE4/1 stations will feature improved Resistive Plate Chambers (iRPC). Distinguished by a unique design and geometry, including a 2D strip readout, these iRPCs represent a significant advancement over the current RPC system. The enhancements include the use of thinner electrodes, a narrower 1.4 mm gas gap, and improved Front-End Board (FEB) allowing a 30 fC threshold. Two iRPC chambers were installed in station 3 of CMS during the year end technical stop (YETS) 2023/2024 and other 70 are being assembled at CERN and being prepared for installation next YETS 2024/2025. This paper provides a comprehensive summary of quality control (QC) and future plans for iRPC chambers in CMS detector.

Improved resistive plate chambers for HL-LHC upgrade of CMS

In view of the High Luminosity LHC, the CMS Muon system will be upgraded to sustain its efficient muon triggering and reconstruction performance. Resistive Plate Chambers (RPC) are dedicated detectors for muon triggering due to their excellent timing resolution. The RPC system will be extended up to 2.4 in pseudorapidity. Before the LHC Long Shutdown 3, new RE3/1 and RE4/1 stations of the forward Muon system will be equipped with improved Resistive Plate Chambers (iRPC) having, compared to the present RPC system, a different design and geometry and 2D strip readout. This advanced iRPC geometry configuration allows the rate capability to improve and hence survive the harsh background conditions during the HL-LHC phase. Several iRPC demonstrator chambers were installed in CMS during the recently completed 2nd Long Shutdown to study the detector behaviour under real LHC conditions. This paper summarizes the iRPC project and its schedule, including the status of the iRPC production sites, details of the chamber quality control procedures and results of the commissioning of the demonstrator chambers.

GEM detectors for the CMS endcap muon system: status of three new detector stations

The High-Luminosity LHC (HL-LHC, or Phase-2 LHC) will deliver proton-proton collisions at 5–7.5 times the nominal LHC luminosity, with an expected number of 140–200 pp-interactions per bunch crossing (Pile-up or PU). To maintain the performance of muon triggering and reconstruction under high background, the forward part of the Muon Spectrometer of the CMS experiment will be upgraded with Gas Electron Multipliers (GEM) and improved Resistive Plate Chambers (iRPC) detectors [1,2]. A first GEM station (GE1/1) was installed during Long Shutdown 2 (LS2, 2019–2021), a 2nd station (GE2/1) of Triple-GEM detectors will be installed in winter 2023–24 and 2024–25, while a new 6-layer station (ME0) will be installed in the third Long Shutdown (LS3, 2026–2028). GE11 is considered an early Phase-2 upgrade as it will reduce the pT threshold by combining GEM and Cathode Strip Chamber (CSC) hits in the forward muon system at twice the LHC design luminosity (ℒ = 2 · 1034 cm-2 s-1, 50 PU). After a successful start of Run-3 in 2022, with almost 40 fb-1 collected, the commissioning of the GE1/1 detector is nearly complete. Most chambers are operated stably with an efficiency in excess of 95%, next being the demonstration of the combined CSC-GEM trigger in 2023. The lessons learnt with the first large-area GEM station have lead to improvements in detector and electronics design for the Phase 2 detectors GE2/1 and ME0. This proceeding will discuss the progress made since last MPGD Conference (MPGD 2019) [3], discussing the commissioning and early performance of GE1/1; the design improvements and start of construction of GE2/1; and the R&D currently ongoing for ME0.

Effect of mesh geometry on resistive Micromegas for the ATLAS experiment

The ATLAS Experiment will use resistive Micromegas detectors for the upgrade of the forward Muon System (NSW, for New Small Wheel). With the test of the first production modules, instabilities in the detector operation have been observed, leading to a systematic revision of the selected construction components and working parameters. In particular, the effect of the mesh geometry with respect to the discharge behaviour was studied using a special Micromegas detector designed and built by the ATLAS CERN group in 2014. The detector has a Micromegas structure similar to the one later on adopted by the NSW project; moreover it provides the possibility to easily replace the mesh. The test procedure consisted in measuring current, gain and counting rate from a 55Fe X-ray source, as a function of the amplification voltage up to the discharge limit. The systematic analysis of the data allowed us to draw conclusions on the stability interval of six different types of mesh, including the one chosen to be used for the NSW, consistent with the expectations. Results suggested that the mesh selected for the NSW (among the few available in the requested big size), was not optimal for operation with a safe plateau at high gain before discharges start to occur. After the present study, cost constraint and available dimension constraints prevented the replacement of the chosen baseline design, which is already available. A post-publication change was made to this article on 25 Jun 2020 to correct the pdf header.

Effect of deformation due to stretching of the Gas Electron Multiplier (GEM) Foil

The Gas Electron Multiplier (GEM) was first introduced by Fabio Sauli in 1997, which is a thin layer of an insulating polymer, coated on both sides with copper and chemically perforated with a high density of microscopic holes. The GEM detectors, which are built using GEM foils, have been utilized for various applications due to their excellent spatial resolution, high rate capabilities and flexibility in design. Large area of triple GEM detectors are planned in experiments as it is the case in the upgrade of the CMS forward muon system. During the assembly of these detectors, the GEM foils are manually stretched to maintain the required gap configuration throughout the detector area. This stretching procedure can introduce local variation in the size or the shape of the perforated holes in GEM foil which can further vary the operational characteristics of the foil as well as the detector. Therefore, the distribution and size of the holes over a GEM foil should be uniform to achieve homogeneous functionality of the detector over the active surface. We can prevent the deformation of the perforated holes by optimizing the stretching force which is used during the assembly.

Quality control for the first large areas of triple-GEM chambers for the CMS endcaps

The CMS Collaboration plans to equip the very forward muon system with triple-GEM detectors that can withstand the environment of the High-Luminosity LHC. This project is at the final stages of R&D and moving to production. An unprecedented large area of several 100 m2 are to be instrumented with GEM detectors which will be produced in six different sites around the world. A common construction and quality control procedure is required to ensure the performance of each detector. The quality control steps will include optical inspection, cleaning and baking of all materials and parts used to build the detector, leakage current tests of the GEM foils, high voltage tests, gas leak tests of the chambers and monitoring pressure drop vs. time, gain calibration to know the optimal operation region of the detector, gain uniformity tests, and studying the efficiency, noise and tracking performance of the detectors in a cosmic stand using scintillators.

Overview of large area triple-GEM detectors for the CMS forward muon upgrade

In order to cope with the harsh environment expected from the high luminosity LHC, the CMS forward muon system requires an upgrade. The two main challenges expected in this environment are an increase in the trigger rate and increased background radiation leading to a potential degradation of the particle ID performance. Additionally, upgrades to other subdetectors of CMS allow for extended coverage for particle tracking, and adding muon system coverage to this region will further enhance the performance of CMS.Following an extensive R&D program, CMS has identified triple-foil gas electron multiplier (GEM) detectors as a solution for the first muon station in the region 1.6<|η|<2.2, while continuing R&D is ongoing for additional regions.

Muon Physics at Run-I and its upgrade plan

The Large Hadron Collider (LHC) and its multi-purpose Detector, ATLAS, has been operated successfully at record centre-of-mass energies of 7 and TeV. After this successful LHC Run-1, plans are actively advancing for a series of upgrades, culminating roughly 10 years from now in the high luminosity LHC (HL-LHC) project, delivering of order five times the LHC nominal instantaneous luminosity along with luminosity leveling. The final goal is to extend the data set from ab increase, the ATLAS detector needs to be upgraded. The upgrade will proceed in two steps: Phase I in the LHC shutdown 2018/19 and Phase II in 2023-25. The largest of the ATLAS Phase-1 upgrades concerns the replacement of the first muon station of the high- rapidity region, the so called New Small Wheel. This configuration copes with the highest rates expected in Phase II and considerably enhances the performance of the forward muon system by adding triggering functionality to the first muon station. Prospects for the ongoing and future data taking are presented. This article presents the main muon physics results from LHC Run-1 based on a total luminosity of 30 fb^-1. Prospects for the ongoing and future data taking are also presented. We will conclude with an update of the status of the project and the steps towards a complete operational system, ready to be installed in ATLAS in 2018/19.

Muon Physics at Run-I and its upgrade plan

The Large Hadron Collider (LHC) and its multi-purpose Detector, ATLAS, has been operated successfully at record centre-of-mass energies of 7 and TeV. After this successful LHC Run-1, plans are actively advancing for a series of upgrades, culminating roughly 10 years from now in the high luminosity LHC (HL-LHC) project, delivering of order five times the LHC nominal instantaneous luminosity along with luminosity leveling. The final goal is to extend the data set from about few hundred fb−1 expected for LHC running to 3000 fb−1 by around 2030. To cope with the corresponding rate increase, the ATLAS detector needs to be upgraded. The upgrade will proceed in two steps: Phase I in the LHC shutdown 2018/19 and Phase II in 2023-25. The largest of the ATLAS Phase-1 upgrades concerns the replacement of the first muon station of the highrapidity region, the so called New Small Wheel. This configuration copes with the highest rates expected in Phase II and considerably enhances the performance of the forward muon system by adding triggering functionality to the first muon station. Prospects for the ongoing and future data taking are presented. This article presents the main muon physics results from LHC Run-1 based on a total luminosity of 30 fb^-1. Prospects for the ongoing and future data taking are also presented. We will conclude with an update of the status of the project and the steps towards a complete operational system, ready to be installed in ATLAS in 2018/19.

The performance and long term stability of the D0 Run II forward muon scintillation counters

The performance of the D0 experiment forward muon scintillation counters system during Run II of the Tevatron from 2001 to 2011 is described. The system consists of 4214 scintillation counters in six layers. The long term stability of the counters amplitude response determined using LED calibration system and muons produced in proton–antiproton collisions is presented. The averaged signal amplitude for counters of all layers has gradually decreased over ten years by 11%. The reference timing, determined using LED calibration, was stable within 0.26ns. Averaged value of muon timing peak position was used for periodic D0 clock signal adjustments to compensate seasonal drift caused by temperature variations. Counters occupancy for different triggers in physics data collection runs and for minimum bias triggers are presented. The single muon yields versus time and the luminosity dependence of yields were stable for the forward muon system within 1% over 10 years.

Development and performance of large scale triple GEM for CMS

The international CMS GEM collaboration is studying the feasibility of upgrading the CMS forward muon system by adding layers of triple GEM based detectors. After successful tests of small size tripe-GEM chambers in the period of 2010-2011, the collaboration has designed, built and tested full-size GEM chambers for the upgrade purpose. We report on results from test beam and simulation that were conducted to study the performance of the GEM chambers.

An ageing study of resistive micromegas for the HL-LHC environment

Resistive-anode micromegas detectors have been in development for several years, in an effort to solve the problem of sparks when working at high flux and high ionizing radiation like in the HL-LHC (up to ten times the luminosity of the LHC). They have been chosen as one of the technologies that will be used in the ATLAS New Small Wheel project (forward muon system). An ageing study is mandatory to assess their capabilities to handle the HL-LHC environment on a long-term period. A prototype has been exposed to several types of irradiation (X-rays, cold neutrons, 60Co gammas and alphas) above the equivalent charge produced in the detector in five HL-LHC running years without showing any degradation of the performance in terms of gain and energy resolution, and with the characterization of the tracking performance in terms of efficiency and spatial resolution, verifying non degradation on the exposed resistive micromegas.

GEM based detector for future upgrade of the CMS forward muon system

In view of an upgrade of the CMS experiment, the GEM for CMS collaboration is performing feasibility studies on employing Triple-GEM detectors for the high-η region (1.6–2.4) of the CMS endcaps. A detailed review of the development and characterization of the CMS full-size prototype baseline detector will be presented. GEMs have excellent spatial and time resolution, high rate capability and radiation hardness, they are an appealing option for simultaneously enhancing muon tracking and triggering capabilities in the high-η region. The GEM for CMS collaboration has studied the performance of small and full-size prototype detectors during several test beam campaigns in order to validate new technologies and techniques in view of a mass production for CMS experiment. Results from measurements with x-rays and from test beam campaigns at the CERN SPS will be shown from both small and large prototypes.

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 investigatingthe possibility of covering the 1.6 < |η| < 2.4 region of the CMS muon endcaps with large-areatriple-GEM detectors. The CMS high-η 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-sizetrapezoidal (1m × 0.5m) triple-GEM prototypes is described. Results from measurementswith x-rays and from test beam campaigns at the CERN SPS is shown for the small andlarge prototypes. Preliminary simulation studies on the expected muon reconstruction andtrigger performances of this proposed upgraded muon system are reported.

Calibration of the scintillation trigger detector of the forward muon system for the D0 experiment

A procedure for LED-based calibration of the scintillation trigger detector of the forward muon system for the D0 experiment on the Tevatron collider at the Fermi National Accelerator Laboratory (Batavia, United States) is presented. During its 4-year operation, the deviation in the signal amplitudes averaged over 4214 counters was 4% or less and the variance (σ) of the distribution of these deviations over all counters was 10%. In the same period of time, the signals remained stable in time with an accuracy of 0.23 ns and the variance (σ) of the distribution of these deviations was 0.52 ns. The calibration procedure based on measuring the amplitude response of the detector counters to muons produced by proton-antiproton collisions at the Tevatron collider is also described. The variations in the absolute value of the amplitude responses over a period of 4 years were in the range of +3%...−9%.

Results of mass testing of mini drift tubes for the D0 forward muon system

The procedures and results of mass testing of mini drift tubes in the course of their production for the D0 forward muon system (Tevatron, Fermilab) are described. High-voltage training, checking the stability and uniformity of signals induced by X rays, measuring the wire tension, and leak testing are included in the testing procedure. Owing to the fast and effective testing of detectors under conditions of mass production, the quality of the mini drift tubes is such that virtually no tubes are finally rejected during assembly of the detector system.

ATLAS muon drift tube production in Seattle

The facility that we developed for producing precision drift tubes of the ATLAS forward muon system is described in this paper. We have completed the production of approximately 30 000 drift tubes in Seattle. The results of quality assurance for these tubes are presented. The drift tube assembly and quality assurance are two separation operations that proceed in parallel. The quality of the drift tube that we produced meets the very stringent requirements of the ATLAS experiment. The typical average production rate is 2 to 3 min per tube and the rejection rate is less than 1.5%.

Restoring contaminated wires, removing gas contaminants, and aging studies of drift tube chambers

The original muon detection system of the Fermilab D0 colliding beam experiment contained 12,000 drift cells 10 cm×5 cm in cross-section and up to 580 cm in length. The gas mixture used was Ar/CF 4/CO 2 (90:6:4). There was one recycling gas system for all the chambers. During the first year of operation, it was discovered that inefficient cells, all in regions of high radiation, had a contaminating shell of crud coating their wires. The source of the contaminant was outgassing of the cathode pads, which were made from a laminate of fiberglass and epoxy/polyester resin, with a copper cladding on one surface. The vapor formed a brittle sheath on the wires, but only in regions of high current discharge due to radiation from the accelerator and colliding beams. A method for cleaning wires in place was devised. By heating the wire quickly to a temperature close to the melting temperature of gold, the sheath was ripped to shreds and blown away. The procedure for “zapping” wires and for removing the contaminating vapor is presented. The upgraded D0 experiment now uses Iarocci-type mini-drift tubes for the forward muon system. The results of aging tests for these chambers are also presented.

Forward muon system for the DØ detector upgrade

The design and main parameters of the completly redesigned DØ Forward Angle MUon System (FAMUS: 1.0<|η|<2.0) for the next high luminosity Tevatron Collider run are reported. Results of the studies of trigger scintillation counters based on fast scintillator Bicron 404A and WLS bars SOFZ-105 are presented. We report about results of test beam studies of prototype counters including minimum ionizing particles detection efficiency, time resolution and amplitude response. Radiation ageing of scintillating materials for the doses up to 1Mrad, phototubes magnetic shielding in the fields of up to 700G and ageing of phototubes are presented. Mini-Drift Tubes (MDTs) are chosen as FAMUS tracking detectors. The detector is a drift wire chamber with a metallic cathode. The detector operates in proportional mode with a fast freon–methane gas mixture to provide high drift velocity, adequate counting rate and low ageing. A description of the performance of the MDT is given. Studies of two prototypes in test beams were performed at FNAL and JINR. Obtained coordinate accuracy is around 0.5mm r.m.s. All tests show robustness of MDT as tracking detector of the new muon system for a long period in high DØ background radiation conditions.

The CDF forward muon system

The general properties of the toroids, drift chambers and trigger counters in the CDF forward muon (FMU) system are discussed. The operation of the PSL time-to-digital converter and the UW HOPU (Half Octant Pattern Unit) module is also described. The forward muon level 1 trigger is presented.