Muon Identifier Research Articles

Experience gained about Resistive Plate Chambers ageing from the ALICE Muon TRigger/IDentifier detector

The ALICE Muon IDentifier is composed of 72 single-gap bakelite Resistive Plate Chambers, which have been operational since 2009 in avalanche mode with a Tetrafluoroethane/Isobutane/Sulphur Hexafluoride gas mixture, undergoing counting rates of the order of tens of Hz/cm2.Here, the long-term performance and stability of the RPC system will be discussed, in terms of efficiency, dark current and dark rate. An assessment of potential signs of ageing observed in the detectors will be presented, together with a summary of the most common hardware problems experienced.

Characterisation of plastic scintillator paddles and lightweight MWPCs for the MID subsystem of ALICE 3

The ALICE collaboration is proposing a completely new detector, ALICE 3, for operation during the LHC Runs 5 and 6. One of the ALICE 3 subsystems is the Muon IDentifier detector (MID), which has to be optimised to be efficient for the reconstruction of J/ψ at rest (muons down to p T ≈ 1.5 GeV/c) for |η| < 1.3. Given the modest particle flux expected in the MID of a few Hz/cm2, technologies like plastic scintillator bars (≈ 1 m length) equipped with wavelength-shifting fibers and silicon photomultiplier readout, and lightweight Multi-Wire Proportional Chambers (MWPCs) are under investigation. To this end, different plastic scintillator paddles and MWPCs were studied at the CERN T10 test beam facility. This paper reports on the performance of the scintillator prototypes tested at different beam momenta (from 0.5 GeV/c up to 6 GeV/c) and positions (horizontal, vertical, and angular scans). The MWPCs were tested at different momenta (from 0.5 GeV/c to 10 GeV/c) and beam intensities, their efficiency and position resolutions were verified beyond the particle rates expected with the MID in ALICE 3.

Commissioning and first performances of the ALICE MID RPCs

ALICE (A Large Ion Collider Experiment) at the CERN Large Hadron Collider (LHC) is designed to study pp and Pb–Pb collisions at ultra-relativistic energies. ALICE is equipped with a Muon Spectrometer (MS) to study the heavy charmonia in pp and heavy ion collisions via their muonic decay. At first, in the LHC Run 1 and 2 the selection of interesting events for muon physics in the MS was performed with a dedicated Muon Trigger system based on Resistive Plate Chambers (RPCs) operated in maxi-avalanche mode. During the LHC Long Shutdown 2 (LS2), ALICE underwent a major upgrade of its apparatus in order to fully profit from the increased luminosity of Pb–Pb collisions (from 20 kHz in Run 2 to 50 kHz in Run 3). Many sub-systems of the ALICE experiment are now running in continuous readout (triggerless). In this context the Muon Trigger system became the Muon IDentifier (MID). In order to reduce the RPC ageing and to increase the rate capability, it was decided to use a new front-end electronics FEERIC with a pre-amplification stage to minimize the charge released per hit inside the gas gap. A description of the MID upgrades, together with the results and performances of the RPCs from the commissioning, is presented in this paper.

ALICE upgrades for Run 4 and Run 5

In view of Run 4 at the LHC, presently scheduled from 2029 onwards, ALICE is pursuing several upgrades to further extend its physics reach. In order to improve heavy-flavor hadron and dielectron measurements which rely on secondary vertexing, a reduction of the material budget of the innermost layers of the Inner Tracking System is needed. This can be achieved with bent pixel sensors, arranged in half-cylinder shapes with integrated power lines and data buses, allowing to get rid of most of the supporting structure and of the water cooling. Moreover, a new Forward Calorimeter (FoCal), covering pseudorapidities of 3.2<η<5.8, has been proposed to measure small-x (down to 10−6) gluon distributions via prompt photon production. The FoCal will be composed of a highly granular Si+W electromagnetic calorimeter combined with a conventional sampling hadronic calorimeter, and will significantly enhance the scope of ALICE for inclusive and correlation measurements with mesons, photons, and jets. For Run 5 and beyond, the ALICE 3 project has been proposed. It consists of a novel compact detector based on monolithic silicon sensors, with ultra-thin layers near the vertex, high readout rate capabilities, superb pointing resolution, excellent tracking and particle identification over a large acceptance. Such a detector enables a rich physics program, ranging from electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector. For particle identification, a sequence of detector systems is foreseen: a combination of a Time-Of-Flight system, a Ring-Imaging Cherenkov detector, an electromagnetic calorimeter, a muon identifier, and a dedicated forward detector for ultra-soft photons. In these proceedings, the upgrade plans will be shown together with the status of R&D on ITS3 and FoCal and with the concepts and requirements of ALICE 3.

Studies on tetrafluoropropene-CO2 based gas mixtures for the resistive plate chambers of the ALICE Muon IDentifier

Due to their simplicity and comparatively low cost, Resistive Plate Chambers are gaseous detectors widely used in high-energy and cosmic rays physics when large detection areas are needed. However, the best gaseous mixtures are currently based on tetrafluoroethane, which has the undesirable characteristic of a large Global Warming Potential (GWP) of about 1400 and because of this, it is currently being phased out from industrial use. As a possible replacement, tetrafluoropropene (which has a GWP close to 1) has been taken into account.Since tetrafluoropropene is more electronegative than tetrafluoroethane, it has to be diluted with gases with a lower attachment coefficient in order to maintain the operating voltage close to 10 kV. One of the main candidates for this role is carbon dioxide. In order to ascertain the feasibility and the performance of tetrafluoropropene-CO2 based mixtures, an R&D program is being carried out in the ALICE collaboration, which employs an array of 72 Bakelite RPCs (Muon Identifier, MID) to identify muons. Different proportions of tetrafluoropropene and CO2, with the addition of small quantities of isobutane and sulphur hexafluoride, have been tested with 50 × 50 cm2 RPC prototypes with 2 mm wide gas gap and 2 mm thick Bakelite electrodes.In the presentation, results from tests with cosmic rays will be presented, together with data concerning the current drawn by a RPC exposed to the gamma-ray flux of the Gamma Irradiation Facility (GIF) at CERN.

Conceptual design report of the MPD Cosmic Ray Detector (MCORD)

This report presents a concept of constructing a detector dedicated for detection of muons observed during measurements carried out at the MPD (Multi-Purpose Detector) detector that is currently under construction at the NICA facility, Russia, Dubna. It has been proposed to design and build an additional detector that will complement the current MPD set and increase its measurement capabilities. The main goal of this project is to provide information from cosmic muons that pass the MPD detector in both in-beam and off-beam experiments. Hence, the detector is called the MPD COsmic Ray Detector (MCORD).The conceptual design of MCORD is proposed by a Polish consortium NICA-PL comprising several Polish scientific institutions.The data from cosmic ray muons could be used as a trigger for calibration of other detection systems comprising the MPD detector. Large surface covered by the MCORD offers also possibility for efficient registration of muons generated in expanding atmospheric showers induced by distant sources. Moreover, beyond some energy threshold, observation of muons originating from decays of collision products will also be possible. In this report examples of the MCORD functionality as a part of the MPD detector are presented.The MCORD is designed as a universal, fast triggering system built as a modular reconfigurable construction. The detection system will be based on plastic scintillators equipped with wavelength shifting fibers, and silicon photomultipliers (SiPM) will be used for scintillation readout. The online analysis of received signals will be performed using digital FPGA modules. Due to the modular design, the same system (its small part) can be used for both laboratory testing of other MPD sub-detectors, and the calibration of these detectors after placing them inside the MPD in off-beam mode. The full detector will support these systems as an additional trigger, calibrator, and muon identifier during the normal operation of the MPD detector with the beam. Thanks to its unique construction, it will expand the possibilities of collecting scientific data of the MPD detector with astrophysical observations.The publication will show the assumptions of the mechanical structure and electronic systems of the planned detector. The installation site of the detector as part of the MPD detector will be described in detail. In the following, the results of simulations made in preparation for this project will be presented. In particular, simulations with the CORSIKA code present angular distributions of particles in cosmic showers in the Dubna city region. Since muons dominate the cosmic ray showers, the MPD detector response to expected cosmic muon flux was also simulated. The results provide information about the muon cut-off thresholds depending on the MPD detector composition during the installation campaign. Simulations of muon events that could be used for MPD subsystems calibration were also performed. The results shown for various configuration of MCORD detector modules will enable the estimation of the time necessary to perform such tests in the future.Simulations with UrQMD model shows the muon abundances due to beam-beam collisions. Approximately 90% of muons are created from pions, whereas the number of muons that reach the MCORD detector is 10 times greater than the number of pions. The MPD detector response was also simulated under the influence of a stream of various particles, especially muons. It shows energy dependence of muon transmission coefficient for MPD with and without ECal assembled. Assuming requirement for muon transmission above 95%, the muon cut-off thresholds are 1.6 GeV and 2.0 GeV, respectively.MCORD detector performance evaluation is also reported. In the case when we used scintillators with one fiber with a diameter of 1 mm, the time resolution of about 1.0 ns was recorded, which corresponds to the positional accuracy (σx) of 7.1 cm. The results of laboratory tests show that application of a 2 mm diameter WLS fiber instead of the previously used 1 mm diameter fiber improves the time resolution to 0.80 ns.

Performance and aging studies for the ALICE muon RPCs

The ALICE muon trigger (MTR) system consists of 72 Resistive Plate Chamber (RPC) detectors arranged in two stations, each composed of two planes with 18 RPCs per plane. The detectors are operated in maxi-avalanche mode using a mixture of 89.7% C2H2F4, 10% i-C4H10 and 0.3% SF6. A number of detector performance indicators, such as efficiency and dark current, have been monitored over time throughout the LHC Run2 (2015–18). While the efficiency showed very good stability, a steady increase in the absorbed dark current was observed.Since the end of 2018, the LHC has entered a phase of long shutdown, during which the ALICE experiment will be upgraded to cope with the next phase of data taking, expected in 2021. The MTR is undergoing a major upgrade of the front-end and readout electronics, and will change its functionalities, becoming a Muon Identifier [1]. Only the replacement of the most irradiated RPCs is planned during the upgrade. It is therefore important to perform dedicated studies to gain further insights into the status of the detector. In particular, two RPCs were flushed with pure Ar gas for a prolonged period of time and a plasma was created by fully ionizing the gas. The output gas was analyzed using a Gas Chromatograph combined with a Mass Spectrometer and the possible presence of fluorinated compounds originating from the interaction of the plasma with the detector inner surfaces has been assessed using an Ion-Selective Electrode station.This contribution will include a detailed review of the ALICE muon RPC performance at the LHC;the procedure and results of the argon plasma test, described above, are also discussed.

The ALICE Muon IDentifier (MID)

During the LHC Run-I (2010–2013) and Run-II (2015–2018), the selection of interesting events for muon physics in ALICE was performed with a dedicated muon trigger system, composed of 72 single-gap phenolic Resistive Plate Chambers (RPCs) operated with current front-end electronics (ADULT FEE) that provides no amplification for the detector pulses. From Run-III starting in 2021 on, in order to fully profit from the increased luminosity of Pb-Pb collisions, the ALICE experiment will run in continuous readout (triggerless) mode and the Muon TRigger system (MTR), therefore, plays the role of a Muon IDentifier (MID). The read-out electronics is being upgraded in order to support continuous readout. Furthermore, in order to increase the RPC rate capability and to mitigate possible aging effects, it is advantageous to operate the detectors with a lower gain avalanche mode by using higher sensitive FEE. Therefore, we decided to replace the current FEE cards with new ones named Front-End Electronics Rapid Integrated Circuit (FEERIC) equipped with an amplification stage. Also, an upgrade of the threshold distribution system to the front-end will allow one to tune thresholds at the single front-end card level, while this was previously only possible at the single-RPC level. Finally, since some of the RPCs currently installed in ALICE have accumulated charges significantly comparable to the value that is expected in their lifespan, roughly 25% of the detectors are planned to be replaced by new ones constructed with new phenolic high-pressurized laminates (HPL). A detailed description of the MTR upgrade and of its current status will be presented in this contribution.

R&D studies on eco-friendly gas mixtures for the ALICE Muon Identifier

The gas mixture for the Resistive Plate Chambers (RPCs), used for the Muon Spectrometer of the ALICE experiment at CERN LHC, is made up of C2H2F4, SF6 and iC4H10. Since the first two gases have high Global Warming Potentials (GWPs), they will be phased out of production in the next years due to the recent European Union regulations; meanwhile their cost is progressively increasing. Therefore, finding a new eco-friendly gas mixture has become extremely important. In order to identify a gas mixture suited to cope with the requirements of the ALICE Muon Identifier in the forthcoming High-Luminosity runs, R&D studies have been performed on promising gas mixtures with small-size RPCs. Hydrofluoroolefins (HFOs) may substitute C2H2F4 thanks to their very low GWPs, especially HFO1234ze. Several tests on HFO-based mixtures are ongoing and encouraging results have already been obtained. Furthermore, the use of CO2 as a quencher has been studied, along with medium-term stability of detectors exposed to the cosmic-ray flux.

The upgrade of the RPC-based ALICE Muon Trigger

The ALICE Muon Trigger is currently yielded by a detector composed of 72 Bakelite single-gap Resistive Plate Chambers operated in maxi-avalanche mode, arranged in four 5.5×6.5 m2 detection planes. In order to meet the requirements posed by the forthcoming LHC high luminosity runs starting from 2021 onwards, in which ALICE will be read out in continuous mode, the Muon Trigger will become a Muon Identifier and will undergo a major upgrade. In the current setup, signals from about 21 k strips are discriminated by 2400 non-amplified Front End (FEE) cards, whose thresholds are provided by external analog voltages (one for each chamber side). All these cards will be replaced with discriminators equipped with a pre-amplification stage which will allow a reduction in the operating high voltage of the detectors, thus prolonging their lifetime. Furthermore, their reference thresholds will be passed via wireless (and I2C chained per chamber side) allowing the tuning of the values at the single card level. Moreover, the 24 most exposed chambers will be replaced with new ones, equipped with high-quality (i.e. smoother surface) Bakelite laminates. The tests performed on the new FEE cards, used both in a test bench and on detectors, and on the new RPC chambers (with cosmic rays) are reported.

The LBNE near detector

The Long-Baseline Neutrino Experiment (LBNE) is a next generation neutrino oscillation experiment currently proposed for construction in the United States with the main goal of studying muon (anti)neutrinos oscillations into electron (anti)neutrinos over a distance greater than 1000 km and over a wide range of neutrino energies. Its main physics results will be the precision measurement of δCP and all three mixing angles. A value of δCP different from 0 or π will appear in the LBNE data as a small (0% to 40%) asymmetry on the oscillation probability of neutrinos versus antineutrinos. Such a small effect requires a very good control of the systematic uncertainties affecting the measurement and this can only been accomplished using a near detector. I will describe the LBNE near detector complex focusing primarily on its reference design, which includes a set of muon detectors to monitor the beam and a magnetized liquid argon TPC surrounded by a muon identifier detector to measure neutrino interactions at the near site.

Chapter 2 The BES-III Detector and Offline Software

The following sections are included: Overview of the BES-III Detector BES-III Offline Software Main Drift Chamber Time-Of-Flight System Electromagnetic Calorimeter Muon Identifier Trigger

Quality control and database on resistive plate chambers for the BESIII experiment

The chamber production and installation of the BESIII MUON identifier system have been finished. The cosmic ray test result after installation shows that the average efficiency is bigger than 95% and can meet the requirement of the design report. A database including all the chamber parameters and performance data has been constructed and is accessible online. The quality control procedures during the production and the database are described.

A new surface treatment for the prototype RPCs of the BESIII spectrometer

The prototype resistive plate chambers (RPCs) for the BESIII spectrometer were constructed by using resistive electrodes made from a special type of phenolic paper laminates developed by us. The surface quality of these laminates is superior to other bakelite plates that have been used to construct RPCs elsewhere. A method for adjusting the resistivety of these laminates was also developed. Extensive studies were conducted by using a number of prototype RPCs in the last several years. Tests have shown prototype RPCs made by using our resistive plates without the linseed oil treatment can achieve the level of performance comparable to RPCs with linseed oil treated bakelite or resistive glass electrodes. In this paper, we will discuss the construction of these prototype RPCs. The test results of a prototype RPC that have been monitored for a year will be reported. Based on favorable test results of prototypes, the RPC production for the muon identifier of the BESIII spectrometer has started at the Beijing Gaonengkedi Science and Technology Co. Ltd. in early 2004 using the technology that we developed.

PHENIX Muon Arms

The PHENIX Muon Arms detect muons at rapidities of | y|=(1.2–2.4) with full azimuthal acceptance. Each muon arm must track and identify muons and provide good rejection of pions and kaons (∼10 −3). In order to accomplish this we employ a radial field magnetic spectrometer with precision tracking (Muon Tracker) followed by a stack of absorber/low resolution tracking layers (Muon Identifier). The design, construction, testing and expected run parameters of both the muon tracker and the muon identifier are described.

The PHENIX detector magnet subsystem

The PHENIX [Photon Electron New Heavy Ion Experiment] Detector is one of two large detectors presently under construction for RHIC (Relativistic Heavy Ion Collider) located at Brookhaven National Laboratory. Its primary goal is to detect a new phase of matter; the quark-gluon plasma. In order to achieve this objective, the PHENIX Detector utilizes a complex magnet subsystem which is comprised of two large magnets identified as the Central Magnet and the Muon Magnet. Muon Identifier steel is also included as part of this package. The entire magnet subsystem stands over 10 meters tall and weighs in excess of 1900 tons. Magnet size alone provided many technical challenges throughout the design and fabrication of the project. In addition, interaction with foreign collaborators provided the authors with new areas to address and problems to solve. Russian collaborators would fabricate a large fraction of the steel required and Japanese collaborators would supply the first coil. This paper describes the overall design of the PHENIX magnet subsystem and discusses its present fabrication status.

The Fermilab external muon identifier and internal picket fence

The development and use of electronic detectors, external to the liquid volume of the Fermilab 15-foot cryogenic bubble chamber, are described. This hybrid system greatly improved the analysis of neutrino-produced bubble chamber events, especially those involving final state muons.

The digital data acquisition chain and the cosmic ray trigger system for the SLD warm iron calorimeter

The entire data acquisition chain, from the custom made front-end electronics to the Fastbus readout and data reduction module, for the digital readout of the SLD (see ref. [1]: SLD design report, SLAC-Report 73 (1984)) limited streamer tube Warm Iron Calorimeter and Muon Identifier is described. Also described is a Fastbus cosmic logic unit being developed to achieve the capability of reading cosmic ray events, also during the intercrossing time, for apparatus monitoring and calibration purposes.

Determination of the neutral current chiral coupling constants uL2, uR2, dL2 and dR2 from a neutrino and antineutrino deuterium experiment

The ratios of neutral-current to charged-current cross sections of v and v interactions, seperately, on proton and neutron targets have been measured. The Big European Bubble Chamber (BEBC), filled with deuterium and equipped with an external muon identifier (EMI) and an internal picket fence (IPF), was exposed to the CERN SPS (anti)neutrino wide-band beam. The measured ratios are R vp= = 0.405 ± 0.024 ± 0.021 , R vn = 0.243 ± 0.013 ± 0.016, R v p = 0.301 ± 0.027 ± 0.024 and R v n = 0.490 ± 0.050 ± 0.037 . (The first error is statistical and the second systematic). From combinations of these ratios the following neutral-current chiral coupling constants have been determined: u L 2 = 0.099 ± 0.018 ± 0.008, d L 2 = 0.202 ± 0.020 ± 0.019, u R 2 = 0.020 ± 0.016 ± 0.009 and d R 2 = 0.002 ± 0.017 ± 0.010. These results agree with the predictions of the SU(2) × U(1) standard electroweak model. Assuming ϱ = 1, the corresponding value of sin 2 θ w is found to be 0.247 ± 0.029, whereas a two-parameter fit to the data yields sin 2 θ w = 0.243 ± 0.046 and ϱ = 0.996 ± 0.041.

A new method to identify muons in an extensive air shower array

Using position-sensitive detectors for the detection of extensive air showers presents a new possibility to identify muons by exploiting the electromagnetic interactions in a thin, high-Z absorber. The fact that these detectors track each charged particle allows the use of a thin layer of material as the muon identifier. The authors' Monte Carlo studies indicate that by using 2.6 radiation lengths of high-Z absorber as a muon detector, a simple algorithm will correctly identify 98% of electrons as electrons and 96% of muons as muons for a cut-off angle of 100 mrad.