RPC Detector Research Articles

Fabrication and testing of a 3D double-stack RPC with 30 gas gaps for detection of high energy gammas

Multigap Resistive Plate Chambers (MRPCs) are cost-effective detectors with a high-performance. They are easy to build and offer the possibility to cover large areas. They provide excellent time resolution and potentially good spatial resolution. In this context, a 3D RPC with 15 double-stack layers (30 gas gaps) free of parallax error is fabricated. The designed RPC has a 2D pixelated readout and the induced charge on the ground electrodes, gives the position in the third dimension. The simulation results show that in the X–Y plane the Full Width Half Maximum (FWHM) resolution is around 70 μm for 511 keV gammas, while for the Z-axis, which is perpendicular to the detector plane, a spatial resolution of around 560 μm can be achieved. The fill factor of the proposed detector with a pitch of 6.25 mm for SNR of 17 is around 0.13%, and the maximum achievable fill factor for the same setup and SNR of 42.5 is around 23%. The measured spatial resolution of the detector for a collimated Cs-137 point source is in good agreement with the simulation results. For an isotropic 511 keV gamma source at 0.95 cm distance of RPC detector, the experimental detection efficiency of constructed RPC at 1900V applied voltage is around 2.1%, which with a relative error of 7% is in good agreement with the simulation result obtained by GEANT4 (2.25%). With the same detector, at larger distances of the gamma source from the detector (clinical PET camera) a detection efficiency of around 5.09% is achievable. For small animal PET (100 mm radius) with 18F point source, the spatial resolution (Γ) of a PET system composed by 3D MRPC detectors with 2.25∗2.25 mm2 and 1∗1 mm2 pixel sizes, fabricated by commercial PCB technology (pitch = 6.25 mm) and Microlithography technology (pitch = 1.25 mm), would be 1.64 mm and 0.91 mm, respectively.

On novel front-end electronics for the ATLAS BI RPC upgrade at HL-LHC developed in SiGe BiCMOS technology with a high-resolution rad-hard Time-To-Digital converter embedded

The High Luminosity phase of LHC will require a huge improvement on the ATLAS detector in terms of performance, being the entire apparatus operated in much harsher conditions. The BI project is one of the ATLAS Phase-2 approved upgrades, ensuring the demands coming from the physics for the next 20 years. In this framework, a novel dedicated Front-End electronics has been developed, which exploits a BJT-based preamplifier, a fast discriminator and a high resolution (¡ 100 ps) Time-To-Digital converter in SiGe BiCMOS technology, to vastly enhance the detector rate capability. This front-end electronics is integrated for the first time within the detector Faraday cage, largely reducing the effects of spurious noise and allowing a minimum effective charge threshold on the induced signal of 1-2 fC. The integration of the front-end electronics directly within the detector Faraday cage is also permitted by the low power consumption of 15 mW/ch. The RPC coupled with this novel front-end electronics represents a new generation of large area timing detectors, granting a record time resolution of 350 ps on a single gas gap of 1 mm with 1.2 mm electrodes thickness and operated with the ATLAS standard gas mixture. The effect of the extremely low threshold has also an impact on the gas mixture, enabling the usage of eco-friendly gas mixtures which would not be usable elsewise. The latest performance of this newly developed front-end electronics along with the results achieved with RPC detector coupled with it will be shown.

Expected performance of Cosmic Muon Veto Detector

The India-based Neutrino Observatory (INO) collaboration has established a miniICAL detector, at the transit campus of IICHEP, Madurai, India, which serves as a prototype detector of the larger Iron-Calorimeter detector (ICAL). The purpose of miniICAL lies in unraveling the intricate physics and engineering challenges inherent in constructing and operating a substantial ICAL-type detector. To explore the feasibility of building a large-scale neutrino experiment at shallow depths the collaboration has embarked upon the construction of a Cosmic Muon Veto Detector (CMVD) around the miniICAL detector. The primary objective of this endeavor revolves around attaining a veto efficiency surpassing 99.99%, while simultaneously maintaining a false-positive rate lower than 10-5. The CMVD system is based on extruded plastic scintillators (EPS) and utilizes wavelength-shifting fibers to collect scintillation photons and uses silicon photomultipliers (SiPMs) as photo-transducers. A software tool is developed for CMVD and is integrated with the existing miniICAL consisting of RPC detectors. The simulation is tuned to include properties of EPSs and WLS fibers, measured efficiencies, and time resolutions of EPSs. Measured spectra and noise in SiPMs are also taken into account. The muon tracks in the RPCs are used to estimate the muon veto efficiency of CMVD to arrive at efficient muon veto criteria. With improved veto efficiency of cosmic muons, the CMVD experiment will help to pave the way for future large-scale shallow-depth neutrino experiments e.g. INO-type experiments, enhancing our understanding of neutrino properties.

Studies of eco-friendly gas mixtures for RPC detectors

In the context of climate change, one of the main contributors to global warming is the greenhouse effect. Regulations have been implemented in different areas of society to reduce or ban the use of Greenhouse Gases (GHG), such as Tetrafluoroethane (TFE). Despite the fact that large-scale experiments (such as the ones held at CERN) have been excluded from these restrictions, it is necessary to look for alternatives more eco-friendly to the environment. In this work we present performance studies for RPC detectors using eco-friendly gas mixtures tested at the Gamma Irradiation Facility (GIF++) at CERN in the context of the Phase II upgrade of the CMS detector.

Status of the MDT Trigger Processor for the ATLAS Level-0 Muon trigger at the HL-LHC

The MDT Trigger Processor (MDTTP) is a key ATLAS Level-0 Muon trigger upgrade component designed to meet High-Luminosity LHC requirements. The MDTTP will use MDT hits in the hardware level trigger for the first time in ATLAS to improve the momentum resolution of muon candidates provided by RPC and TGC detectors and reduce the fake muon trigger rate.The MDTTP hardware is based on the Apollo ATCA platform. The prototype includes a VU13P-FPGA, high-speed FireFly optical transceivers, peripherals, and other improvements learned from using the previous hardware demonstrator. We present the prototype status, firmware implementation, core algorithm, slow-control software, and first integration tests.

Latest results of Longevity studies on the present CMS RPC system for HL-LHC phase

The present Compact Muon Solenoid Resistive Plate Chambers system has been worked efficiently during Run I and Run II of data taking period (Shah et al., 2020) [1]. In the coming years of operation with the High Luminosity LHC (HL-LHC), the expected rate and integrated charge are expected to be about 600 Hz/cm2 and 840 mC/cm2, respectively (including a safety factor of three). Therefore, the HL-LHC phase will be a challenge for the RPC system since the expected operating conditions are much harsher than those for which the detectors have been designed, and could introduce non-recoverable aging effects which can alter the detector properties. A longevity test has been started at the CERN Gamma Irradiation Facility to estimate the impact of HL-LHC conditions on the RPC detector performance in order to determine whether the RPC system will survive the harsher background conditions expected at HL-LHC. The latest results of the irradiation test will be presented.

Study of RPC ionic signal properties with different read-out methods

The simultaneous measurement of the ionic charge (induced by the slow motion of positive ions inside the gas gap) and of the fast/prompt charge (induced on the read-out electrodes by the drift of electrons) is fundamental for the understanding of the working principles of the RPC detector. Typical RPC electrodes are made of resistive material with the voltage applied on a thin graphite layer, which however alters the reading of the ionic charge depending on the discharge position. We have therefore realized a small RPC detector with a metallic grid deployed in one of the resistive electrodes. The prompt charge is measured by means of typical read-out copper strips with 1.4 cm pitch. The purpose of the study described in this presentation is to test different ion signal read-out systems and the comparison with the prompt signal read out with traditional techniques, to improve the detector knowledge and for possible future applications.

Performance studies of RPC detectors operated with C2H2F4 and CO2 gas mixtures

Resistive Plate Chambers detectors are largely employed at the CERN LHC experiments thanks to their excellent trigger performances and contained costs. They are operated with a gas mixture made of 90%–95% of C2H2F4, that provides a high number of ion–electron pairs, about 5% of i-C4H10, that ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4is known to be a Greenhouse gas, with a global warming potential (GWP) of 1430. CERN has identified several strategies to reduce the consumption of greenhouse gas emissions from particle detectors at LHC experiments. One research line is focused on the study of alternatives to C2H2F4. In this context, a conservative approach for the next years of LHC operation could be to focus on reducing the GWP of the RPC gas mixture by only adding CO2 and not using new gases, whose effects on detector long-term operation have to be studied. The RPC performance with standard gas mixture with the addition of 30%–50% of CO2 (and SF6 concentration between 0.3 and 0.9%) were studied both in laboratory set-up and at the CERN Gamma Irradiation Facility in presence of muon beam and gamma background radiation. Encouraging results were obtained showing that the addition of CO2 to the standard gas mixture can represent a mid-term solution to reduce emissions and lower operational costs by keeping stable detector performance and safe long-term operation.

Performance of improved RPCs demonstrator for the CMS at the HL-LHC

With the increase of the LHC luminosity foreseen in the coming years, components of detectors currently used in the LHC need to be replaced or new ones should be added. The new ones should be capable not only to support the high particle rate, but also to provide time information to reduce the data ambiguity due to the expected high pileup. The CMS collaboration have shown that the RPCs, using smaller gas gap (1.4 mm) and low-resistivity High Pressure Laminate, can stand rates of few kHz/cm2. They are equipped with new electronics sensitive to low signal charges. The electronics was developed to read out the RPC detectors from both sides of a strip and, using timing information, to identify the position along it. The excellent relative resolution of 160 ps leads to a space resolution of 1.5 cm. The absolute time measurement, determined by RPC signal around 500 ps, will also reduce the data ambiguity due to the expected high pileup at the Level 1 trigger. An engineering prototype of the final chamber was qualified in test beams at the Gamma Irradiation Facility (GIF++), located on one of the SPS beam lines at CERN. In addition, 4 demonstrator chambers have just been installed in the CMS cavern. This paper will present the results of the tests done in GIF++, as well as brand new results from the demonstrator chambers.

Advances towards a large-area, ultra-low-gas-consumption RPC detector

Large Resistive Plate Chamber systems have their roots in High Energy Physics experiments at the European Organization for Nuclear Research: ATLAS, CMS and ALICE, where hundreds of square meters of both trigger and timing RPCs have been deployed. These devices operate with complex gas systems, equipped with re-circulation and purification units, which require a fresh gas supply of the order of 6 cm3/min/m2, creating logistical, technical and financial problems.In this communication, we present a new concept in the construction of RPCs which allowed us to operate a detector at ultra-low gas flow regime. With this new approach, the glass stack is encapsulated in a tight plastic box made of polypropylene, which presents excellent water vapor blocking properties as well as a good protection against atmospheric gases.

Construction of an RPC using additive manufacturing technology

In this work, we report the progress in the design and construction of an RPC detector fully built using additive manufacturing technology, an emerging/interdisciplinary engineering domain only partially utilized in HEP. Our novel design of the 3D detector stack can be automatically and fully constructed in a short time, ensuring repeatability and accuracy, while minimizing construction mistakes. 3D printing, applied to instrumentation for physics enhances detector performance and capabilities, cutting construction costs and improving standardization over large-scale productions. The delivered detector constitutes a new generation of RPC detectors, electrically equivalent to the existing ones but mechanically better and standardized according to the prescribed specifications.We aim at proving the feasibility studies of a 3D printed detector that features state-of-art performance, at a fraction of the cost and potentially constructed without the need of external industrial partners.

Track reconstruction and matching between emulsion and silicon pixel detectors for the SHiP-charm experiment

In July 2018 an optimization run for the proposed charm cross section measurement for SHiP was performed at the CERN SPS. A heavy, moving target instrumented with nuclear emulsion films followed by a silicon pixel tracker was installed in front of the Goliath magnet at the H4 proton beam-line. Behind the magnet, scintillating-fibre, drift-tube and RPC detectors were placed. The purpose of this run was to validate the measurement's feasibility, to develop the required analysis tools and fine-tune the detector layout. In this paper, we present the track reconstruction in the pixel tracker and the track matching with the moving emulsion detector. The pixel detector performed as expected and it is shown that, after proper alignment, a vertex matching rate of 87% is achieved.

A data-based machine learning approach for RPC time resolution study based on ToF reconstruction

A data-based machine learning approach is proposed to study the properties of time resolution of RPC detectors by measuring the time of flight of cosmic muons. This method utilises a multi-layer perceptron and a type of recurrent neural network called long short-term memory. The neural network is trained with the waveforms of RPC signals digitized by an oscilloscope at a sampling frequency of 10 GHz and a 2 GHz bandwidth. A data augmentation approach is implemented for labelling. Compared to the results from conventional waveform analysis, this approach achieves a better time resolution of 1-mm gap RPCs. Based on the data, the approach has a generalisation capacity for performance studies of other timing detectors.

Commissioning of the New sMDT Monitored Drift Tube Detectors for the Phase-1 Upgrade of the ATLAS Muon Spectrometer

The Muon Drift Tube (MDT) chambers provide very precise and reliable muon tracking and momentum measurement in the ATLAS muon spectrometer. Already in Run 2 of the LHC they have to cope with very high background counting rates up to 500 Hz/cm{}^{2} in the inner endcap layers. At High-Luminosity LHC (HL-LHC), the background rates are expected to increase by almost a factor of 10. New small (15 mm)-diameter Muon Drift Tube (so-called sMDT) detectors have been developed for upgrades of the muon spectrometer. They provide an order of magnitude higher rate capability and allow for the installation of additional new triplet thin-gap RPC trigger chambers in the barrel inner layer of the muon detector for HL-LHC. They have been designed for mass production at the Max Planck Institute (MPI) for Physics in Munich and achieve a sense of wire positioning accuracy of 5 mum. A pilot project for the barrel inner layer upgrade is underway during the 2019/2021 LHC shutdown. Several sMDT chambers have already been installed and operated in the ATLAS detector. The detailed studies of the muon detection efficiency and muon track resolution have been carried out after the assembling of the sMDT detectors in MPI and repeated at CERN after the integration with the new RPC detectors. The author will describe the detector design, the quality assurance and certification path, as well as will present the status of the installation and commissioning, worth its preliminary results and an overview for the complete integration of the sMDT project In the ATLAS experiment.

A high speed frontend electronics ASIC for multi-channel single gap RPC detector

This paper presents a high speed prototype frontend electronics (FEE) ASIC, designed to meet the readout requirements of ∼ 3.6 million channels of avalanche mode single-gap resistive plate chamber detectors of Iron Calorimeter experiment of India based Neutrino Observatory. This ASIC is a regulated cascode transimpedance pre-amplifier based octal amplifier-comparator FEE solution in 0.35 μm CMOS process. Two DC stabilization techniques, one for common mode and another for differential DC offset cancellation, have been incorporated in this ASIC to ensure amplifier baseline stability, uniform dynamic range and comparator overdrive across readout channels. This DC common mode control can also be used to trim the input impedance of regulated cascode pre-amplifier. The ASIC provides parallel LVDS outputs on external 100 Ω load for tracking and precision time-tagging. A multiplexed analog output is also provided through an on-chip 50 Ω cable driver for detector pulse profile analysis. The ASIC has total channel gain of ∼ 0.75 mV/fC for single ended inputs of both the polarities, intrinsic timing precision of ∼ 190 ps RMS and ∼ 100 ps RMS for input charge of 0.1 pC and beyond 0.3 pC respectively with total power consumption of 40 mW/channel.

Front-end electronics for CMS iRPC detectors

A new generation of resistive plate chambers, capable of withstanding high particle fluxes (up to 2000 Hz · cm-2) and instrumented with precise timing readout electronics is proposed to equip two of the four high pseudorapidity stations of the CMS muon system. Double-gap RPC detectors, with each gap made of two 1.4 mm High Pressure Laminate electrodes and separated by a gas gap of the same thickness, are proposed. The new layout reduces the amount of the avalanche charge produced by the passage of a charged particle through the detector. This improves the RPC rate capability by reducing the needed time to collect this charge. To keep the RPC efficiency high, a sensitive, low-noise and high time resolution front-end electronics is needed to cope with the lower charge signal of the new RPC. An ASIC called PETIROC that has all these characteristics has been selected to read out the strips of new chambers. Thin (0.6 mm) printed circuit board, 160 cm long, equipped with pickup strips of 0.75 cm average pitch, will be inserted between the two new RPC's gaps. The strips will be read out from both ends, and the arrival time difference of the two ends will be used to determine the hit position along the strip. Results from the improved RPC equipped with the new readout system and exposed to cosmic muons in the high irradiation environment at CERN GIF++ facility are presented in this work.

Towards sealed Resistive Plate Chambers

The mitigation of human-induced climate change is of crucial importance for the sustainability of humankind. For this aim the RPC community has exerted considerable effort over the last decade to reduce the greenhouse gases emission from RPC detectors. These included searching for new eco-friendly gases, implementing recovery and/or recirculation systems, improving gas tightness and using new materials and approaches in detector conception and operation for the reduction of gas flow rates. Along this line of work, we present here an RPC architecture aimed at a dramatic reduction of gas use in chambers meant for low particle rate (below ten of Hz⋅cm−2) operation. Two glass chambers were tested for more than six months with zero gas flow, showing no evidence of time-related effects, allowing to consider that permanently sealed RPCs may be within reach, with obvious practical and environmental advantages.

Performance of the BIS78 RPC detectors: a new concept of electronics and detector integration for high-rate and fast timing large size RPCs

The reduction of the average charge per count in the gas along with the capability to discriminate very small signals from noise can allow an efficient and long-term Resistive Plate Chamber detector operation in high radiation background environment. This goal has been reached during the R&D program of the BIS78 upgrade project of the ATLAS detector at LHC through the deep integration of a fast (100 ps peaking time) and sensitive (as small as 100 μV threshold) Front-End electronics (FE) with a very large size detector structure. This innovative RPC integration concept pivots on a newly conceived faraday cage, embedding the readout strips and the FE, tightly wrapped around a 1 mm gas gap RPC with 1.2 mm thick electrodes, as a fully independent singlet structure. We studied the performance of BIS78 production triplet chambers, made of 3 independent singlets of 2 m2, each providing a 2D space and time information, showing a minimum threshold achievable of 3 pC of average charge per count produced inside the gas gap. We show that these chambers grant a record combined performance of better than 95% single gap efficiency, time resolution of 350 ps and 10 kHz/cm2 rate capability.

A neural network based algorithm for MRPC position reconstruction

Over the last ten years, muon imaging has attracted much attention due to its possible applications to detect high-Z materials in shipping containers or image very large objects such as volcanoes and large buildings. Precise measurements of the incident and outgoing angles of the cosmic muons are mandatory in this application. Large size (M)RPC detector with sub-millimetre position resolution should be an ideal candidate for the detector system. Prior work on improving the position resolution of MRPC mainly focuses on adjusting read-out panel and the detector geometry, while little work has been done on improving the position reconstruction algorithm. This paper proposes a new position reconstruction algorithm based on the neural networks which has no systematic error and gives better results than the center of gravity algorithm.

A new approach for CMS RPC current monitoring using Machine Learning techniques

The CMS experiment has 1054 RPCs in its muon system. Monitoring their currents is the first essential step towards maintaining the stability of the CMS RPC detector performance. The current depends on several parameters such as applied voltage, luminosity, environmental conditions, etc. Knowing the influence of these parameters on the RPC current is essential for the correct interpretation of its instabilities as they can be caused either by changes in external conditions or by malfunctioning of the detector in the ideal case. We propose a Machine Learning(ML) based approach to be used for monitoring the CMS RPC currents. The approach is crucial for the development of an automated monitoring system capable of warning for possible hardware problems at a very early stage, which will contribute further to the stable operation of the CMS RPC detector.