Endcap Region Research Articles

Design and construction of the mechanical structure for thin-gap RPC triplets for the upgrade of the ATLAS muon spectrometer

The advent of thin-gap RPCs, with 1 mm gas gaps instead of 2 mm in the present RPCs, opened the possibility to instrument the inner barrel layer of the ATLAS muon spectrometer where there is very limited amount of space in radial direction from the beam line. The environment is particularly dense in the barrel end-cap transition region. A compact mechanical structure coping with the expected thickness variations of the assembled RPCs is needed to fit into the limited available space. At the same time the mechanical structure must be sufficiently rigid to keep the deformations of the RPC packages within the allowed envelopes. The tight space constraints make it impossible to achieve the required rigidity with thick paper honeycomb plates as used in the present ATLAS RPCs. For the phase I upgrade of the barrel end-cap transition region of the ATLAS muon spectrometer three 1 mm gap RPCs are put into an aluminium frame. In this frame the RPC triplet is compressed with pre-bent 2 mm thick aluminium plates. The rigidity of the frame is achieved by stiffening rods connecting the lateral structure of the frame. The same concept can be used for the phase II upgrade of the inner layer of the muon spectrometer.

Gas mixture quality studies for the CMS RPC detectors during LHC Run 2

Resistive Plate Chamber (RPC) detectors are widely employed in the muon trigger systems of three experiments at the CERN Large Hadron Collider (LHC). They are operated with gas mixture recirculation systems to reduce operational costs and greenhouse gas emissions since their gas mixture is based on C2H2F4, which has a high global warning potential. It is well known that the C2H2F4 molecule can break down under the effect of radiation and electric field. This leads to the creation of several impurities and free fluoride ions (F-), which could accumulate under gas recirculation and potentially attach to the RPC bakelite electrode inner surface. For these reasons, an extensive gas analysis campaign has been performed during LHC Run 2 for the CMS RPC system to verify gas mixture quality and possible accumulation of impurities.During the entire LHC Run 2 period, a gas chromatograph has been used to analyze the RPC gas mixture at different points of the gas system: quality of pure C2H2F4, fresh gas from the mixer, gas at the output of the detectors, and after the purifier module. Several impurities have been found and identified. Few impurities are already present in the C2H2F4 supply, as residuals of the industrial production. Nevertheless, it was found that some of these impurities, as well as others, are created inside the detector gas gap due to the fragmentation of the C2H2F4 molecule under the effects of electric field and radiation.During the 2018 LHC Run several gas analysis points were added to measure the fluoride ions production in different sectors of the RPC detector system. Indeed the products of the C2H2F4 fragmentation do not always recombine and F- species can stay free in the gas mixture. F- analyses were performed on the gas at the output of the detectors both for barrel and endcap regions, where radiation levels and operational conditions were different. In this way, it was possible to correlate the F- production with integrated charge, and gas mixture flow rate. In parallel, the RPC currents have been constantly monitored to look for possible correlations.Fluoride measurements have also been performed at GIF++ to better understand the correlation between F- production, radiation levels and gas volume exchanges.A comprehensive overview of the results obtained from the different types of gas analyses and possible correlation with RPC currents and LHC luminosity will be presented.

CLUE: A Fast Parallel Clustering Algorithm for High Granularity Calorimeters in High-Energy Physics

One of the challenges of high granularity calorimeters, such as that to be built to cover the endcap region in the CMS Phase-2 Upgrade for HL-LHC, is that the large number of channels causes a surge in the computing load when clustering numerous digitized energy deposits (hits) in the reconstruction stage. In this article, we propose a fast and fully parallelizable density-based clustering algorithm, optimized for high-occupancy scenarios, where the number of clusters is much larger than the average number of hits in a cluster. The algorithm uses a grid spatial index for fast querying of neighbors and its timing scales linearly with the number of hits within the range considered. We also show a comparison of the performance on CPU and GPU implementations, demonstrating the power of algorithmic parallelization in the coming era of heterogeneous computing in high-energy physics.

The BIS78 Resistive Plate Chambers upgrade of the ATLAS Muon Spectrometer for the LHC Run-3

Resistive Plate Chambers (RPCs) are used in the ATLAS experiment for the muon trigger and two coordinate measurements in the central region. In preparation for the coming years of LHC running at higher luminosity, besides the New Small Wheel project which is expected to complement the ATLAS muon spectrometer in the end-cap regions, a smaller size project, known as BIS78 (from Barrel Inner Small sectors), is being developed with a foreseen installation during the LHC Long Shutdown 2 (2019–2020). The BIS78 project will reinforce the fake muon rejection and the selectivity of the muon trigger in the transition region between the ATLAS barrel and end-caps by adding 32 RPC triplets on the edges of the Inner Barrel even sectors (BIS7 and BIS8) as this region is characterized by high rate due to secondary charged tracks generated by beam halo protons and a lack of detector instrumentation. Each triplet will be a station composed by three independent RPC detectors. Due to the narrow available space, the project foresees to replace the existing Monitored Drift Tubes (MDTs), used for the precise position measurement in this area, with muon stations formed by integrated smaller diameter tubes (sMDT) and a new generation of RPCs, capable of withstanding the higher rates and provide a robust standalone muon confirmation. These new RPCs are based on novel design of the gas volume with a thinner gas gap, thinner resistive electrodes, a lower operating voltage and new high gain front-end electronics with respect to the legacy ATLAS RPCs. Besides the use in Run-3 and onwards, this project is also of particular relevance as a pilot test for the High Luminosity LHC upgrade when an additional full layer of new RPC triplets is expected to complement the full barrel region in the innermost plane. The core of the project is presented, together with a description of the production and the test results. Details on the detector infrastructure and services along with a roadmap towards the final installation and commissioning during the Long Shutdown 2 (2019–2020) are also discussed.

Performance of the ATLAS muon triggers in Run 2

The performance of the ATLAS muon trigger system is evaluated with proton-proton (pp) and heavy-ion (HI) collision data collected in Run 2 during 2015–2018 at the Large Hadron Collider. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons to cover the intermediate momentum range between 26 GeV and 100 GeV. Overall, the efficiency of the single-muon triggers is about 68% in the barrel region and 85% in the endcap region. The pT range for efficiency determination is extended by using muons from decays of Jψ mesons, W bosons, and top quarks. The performance in HI collision data is measured and shows good agreement with the results obtained in pp collisions. The muon trigger shows uniform and stable performance in good agreement with the prediction of a detailed simulation. Dedicated multi-muon triggers with kinematic selections provide the backbone to beauty, quarkonia, and low-mass physics studies. The design, evolution and performance of these triggers are discussed in detail.

A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system: detector concept, description, R&D and beam test results

The increase of the number of interactions at the High Luminosity LHC will have a severe impact on the ATLAS detector reconstruction and trigger performance. The end-cap and forward regions, where the Liquid Argon calorimeter has coarser granularity and the inner tracker has poorer momentum resolution, will be particularly affected. A High Granularity Timing Detector (HGTD) is proposed in front of the Liquid Argon end-cap calorimeters for pile-up mitigation and for luminosity measurement. It will cover the pseudo-rapidity range 2.4 < |η| < 4.0. Two silicon sensors double-sided layers on each end-cap will provide precision timing information for minimum ionising particles in order to assign each particle to the correct vertex. Readout cells have a size of 1.3 × 1.3 mm, leading to a highly granular detector with over 3.6 million channels. The Low Gain Avalanche Detectors (LGAD) technology has been chosen for the HGTD detector as it provides a compact sensor with large signal over noise ratio leading to excellent timing performance. The requirements and overall specifications of the HGTD will be presented. LGAD R&D campaigns were carried out to study the sensors and their radiation hardness. Latest laboratory and test beam results will be presented.

Effects of the electronic threshold on the performance of the RPC system of the CMS experiment

Resistive Plate Chambers have a very important role for muon triggering both in the barrel and in the endcap regions of the CMS experiment at the Large Hadron Collider (LHC) . In order to optimize their performance, it is of primary importance to tune the electronic threshold of the front-end boards reading the signals from these detectors. In this paper we present the results of a study aimed to evaluate the effects on the RPC efficiency, cluster size and detector intrinsic noise rate, of variations of the electronics threshold voltage.

Performance evaluation of the aerogel RICH counter for the Belle II spectrometer using early beam collision data

Abstract The Aerogel Ring Imaging Cherenkov (ARICH) counter serves as a particle identification device in the forward end-cap region of the Belle II spectrometer. It is capable of identifying pions and kaons with momenta up to $4\&amp;gt;$GeV$\&amp;gt;$c$^{-1}$ by detecting Cherenkov photons emitted in the silica aerogel radiator. After the detector alignment and calibration of the probability density function, we evaluate the performance of the ARICH counter using early beam collision data. Event samples of $D^{\ast +} \to D^0 \pi^+ (D^0 \to K^-\pi^+)$ were used to determine the $\pi(K)$ efficiency and the $K(\pi)$ misidentification probability. We found that the ARICH counter is capable of separating kaons from pions with an identification efficiency of $93.5 \pm 0.6 \, \%$ at a pion misidentification probability of $10.9 \pm 0.9 \, \%$. This paper describes the identification method of the counter and the evaluation of the performance during its early operation.

Performance of the Belle II aerogel-based ring-imaging Cherenkov counter system in SuperKEKB 2019 phase 3 operation

In the Belle II experiment, an aerogel-based proximity focusing ring-imaging Cherenkov (ARICH) counter is used for charged particle identification (PID) in the forward end-cap region. The goal is to separate kaons from pions at above 4σ significance level for momenta up to 4 GeV/c, which is critical for the measurements of rare B decays and CP violation in B decays. Chrerenkov photons are emitted in aerogel tiles and 144-channel Hybrid Avalanche Photo Detector (HAPDs) are used as the photo-detectors. We utilize a two-layer aerogel design with different refractive indexes in a focusing configuration. In Phase 3 of the Belle II operation (from Apr. 2019), the ARICH system has been operating smoothly. The performance of particle identification with ARICH has been well validated and is in agreement with simulation.

Design and performance studies of the calorimeter system for a FCC-hh experiment

The physics reach and feasibility of the Future Circular Collider (FCC) with centre of mass energies up to 100 TeV and unprecedented luminosity has delivered a Conceptual Design Report early 2019. 100 TeV proton-proton collisions will produce very high energetic particle showers in the calorimeters from both, jets and composite objects such as boosted bosons/tops. The reconstruction of such objects sets the calorimeter performance requirements in terms of shower containment, energy resolution and granularity. Furthermore, high-precision measurements of photons and electrons over a wide energy range are crucial to fully exploit the FCC-hh physics potential, especially given the large amount of collisions per bunch crossing the detectors will have to face (pile-up of 0⟨ μ ⟩=100). The current reference technologies for the calorimeter system of the FCC-hh detector are presented: Liquid Argon (LAr) as the active material in the electromagnetic calorimeters, and the hadronic calorimeters for |η|>1.3 (Endcap and Forward region), and a Scintillator-Steel (Tile) calorimeter as hadronic calorimeter in the Barrel region. The paper will focus on the performance studies for single particles and jets in the combined calorimeter system. We will introduce the simulation framework and the reconstruction chain, that includes the calibration and clustering of calorimeter cells and the estimation of the electronics as well as the pile-up induced noise. In conclusion, the achieved performances will be compared to the physics benchmarks of the FCC-hh experiment.

Concepts and design of the CMS high granularity calorimeter Level 1 trigger

The CMS collaboration has chosen a novel high granularity calorimeter for the endcap regions as part of its planned upgrade for the high luminosity LHC. The calorimeter will have fine segmentation in both the transverse and longitudinal directions and will be the first such calorimeter specifically optimised for particle-flow reconstruction to operate at a colliding-beam experiment. The calorimeter data will form part of the Level 1 trigger of the CMS experiment and, together with tracking information that will also be available at this level, should allow particle-flow techniques to be used as part of this trigger. The trigger has tight contraints on latency and rate, and will need to be implemented in hardware. The high granularity results in around six million readout channels in total, a million of which are also used as part of the Level 1 trigger, presenting a significant challenge in terms of data manipulation and processing for the trigger system. The trigger data volumes will be an order of magnitude above those currently handled at CMS. In addition, the high luminosity will result in an average of 140 (or more) interactions per bunch crossing that give a huge background rate in the forward region and these will need to be efficiently rejected by the trigger algorithms. Furthermore, reconstruction of the particle clusters to be used for particle flow in events with high hit rates is also a complex computational problem for the trigger. The status of the trigger architecture and design, as well as the concepts for the algorithms needed in order to tackle these major issues, will be presented.

Precision timing with low gain avalanche detectors in the CMS MTD Endcap Timing Layer

The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC (HL-LHC). In particular, precision timing can offset the performance degradation due to event pileup at the HL-LHC, recovering the purity of vertices of current LHC conditions. As such, a new timing layer will be introduced to measure minimum ionizing particles (MIPs) with a time resolution of 30 ps. The endcap region of this MIP Timing Detector (MTD) will be instrumented with a hermetic double layer of silicon low gain avalanche detectors (LGADs), covering the high radiation pseudo-rapidity region between |η|=1.6 to 3.0. Radiation tolerance studies of the LGADs indicate excellent performances adequate to cope with the Endcap Timing Layer (ETL) requirements. The LGADs have intrinsic gain, which enhances the MIP signal and provides adequate signal-to-noise for good timing precision. We present the status of the art for the LGADs for the endcap region of the MTD and report on recent beam test results.

Silicon sensors for the CMS HGCAL upgrade: challenges, sensor design & electrical characterization

The CMS detector will undergo significant improvements to face the 10-fold increase in integrated luminosity of LHC, the so-called High-Luminosity LHC, scheduled to start in 2027. This will include a completely new calorimeter in the CMS endcap regions, which should be able to withstand fluences of up to 1016 neq/cm2. The new High Granularity Calorimeter (HGCAL) will have unprecedented transverse and longitudinal readout and trigger segmentation that will facilitate the particle-flow approach to reconstruct electromagnetic and hadronic particle showers and their energies. In regions of low radiation, HGCAL will be equipped with small plastic scintillator tiles as active material coupled to on-tile silicon photomultipliers. In the higher radiation zone, silicon has been chosen due to its intrinsic radiation hardness. The silicon sensors will be of hexagonal shape, with three nominal thicknesses of 120 μm, 200 μm and 300 μm, optimized for regions of different radiation levels. They will be segmented into several hundred cells with hexagonal shape of 0.5 to 1.1 cm2 in size, each of which is read out individually. A comprehensive campaign is in progress to converge on optimal sensor design choices and parameters, such as bulk doping, layouts and production methods. Results from full electrical sensor characterization are presented for different sensors, together with first results from an irradiation campaign of large-area silicon sensors.

40 MHz Level-1 Trigger Scouting for CMS

The CMS experiment will be upgraded for operation at the HighLuminosity LHC to maintain and extend its physics performance under extreme pileup conditions. Upgrades will include an entirely new tracking system, supplemented by a track finder processor providing tracks at Level-1, as well as a high-granularity calorimeter in the endcap region. New front-end and back-end electronics will also provide the Level-1 trigger with high-resolution information from the barrel calorimeter and the muon systems. The upgraded Level-1 processors, based on powerful FPGAs, will be able to carry out sophisticated feature searches with resolutions often similar to the offline ones, while keeping pileup effects under control. In this paper, we discuss the feasibility of a system capturing Level-1 intermediate data at the beam-crossing rate of 40 MHz and carrying out online analyzes based on these limited-resolution data. This 40 MHz scouting system would provide fast and virtually unlimited statistics for detector diagnostics, alternative luminosity measurements and, in some cases, calibrations. It has the potential to enable the study of otherwise inaccessible signatures, either too common to fit in the Level-1 accept budget, or with requirements which are orthogonal to “mainstream” physics, such as long-lived particles. We discuss the requirements and possible architecture of a 40 MHz scouting system, as well as some of the physics potential, and results from a demonstrator operated at the end of Run-2 using the Global Muon Trigger data from CMS. Plans for further demonstrators envisaged for Run-3 are also discussed.

A High-Granularity Timing Detector (HGTD) for the Phase-II upgrade of the ATLAS detector

The expected increase of the particle flux at the high-luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L = 7.5× 1034 cm−1s−1 will have a severe impact on the ATLAS detector performance. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for electrons, photons as well as jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity and the inner tracker has poorer momentum resolution compared to the central region. A High Granularity Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation and for bunch per bunch luminosity measurements. This device should cover the pseudo-rapidity range of 2.4 to about 4.0. Two Silicon sensors double-sided layers are foreseen to provide a precision timing information for minimum ionizing particle with a time resolution better than 50 pico-seconds per hit (i.e. 30 pico-seconds per track) in order to assign the particle to the correct vertex. Each readout cell has a transverse size of 1.3 mm×1.3 mm leading to a highly granular detector with about 3 millions of readout electronics channels. Low-Gain Avalanche Detector (LGAD) technology has been chosen as it provides an internal gain good enough to reach large signal over noise ratio needed for excellent time resolution. Extensive LGAD research and development (R&D) campaigns are carried out to investigate the suitability of this new technology as timing sensors for HGTD. The related readout ASIC is also being studied extensively.

Deep diffused Avalanche photodiodes for charged particles timing

The upgrades of ATLAS and CMS for the High Luminosity LHC (HL-LHC) highlighted physics objects timing as a tool to resolve primary interactions within a bunch crossing. Since the expected pile-up is around 200, with an r.m.s. time spread of 180ps, a time resolution of about 30ps is needed. The timing detectors will experience a 1-MeV neutron equivalent fluence of about Φeq=1014 and 1015cm−2 for the barrel and end-cap regions, respectively. In this contribution, deep diffused Avalanche Photo Diodes (APDs) produced by Radiation Monitoring Devices are examined as candidate timing detectors for HL-LHC applications. To improve the detector’s timing performance, the APDs are used to directly detect the traversing particles, without a radiator medium where light is produced. Devices with an active area of 8 × 8mm2 were characterized in beam tests. The timing performance and signal properties were measured as a function of position on the detector using a beam telescope and a microchannel plate photomultiplier (MCP-PMT). Devices with an active area of 2 × 2mm2 were used to determine the effects of radiation damage and characterized using a ps pulsed laser. These detectors were irradiated with neutrons up to Φeq=1015cm−2.

A New Interface Board for the Level-1 Muon Barrel Trigger Upgrade of the ATLAS Experiment

The Level-1 barrel trigger of the ATLAS experiment is based on the resistive plate chambers (RPCs) detectors. The on-detector trigger electronics identifies muons with specific values of transverse momentum, by using coincidences between different layers of detectors. Trigger data are then transferred from on-detector to off-detector trigger electronics boards. Data are processed by a complex system, which combines trigger data from the barrel and the end-cap regions and provide the combined muon candidate to the central trigger processor (CTP). The system has been performing well for almost a decade. However, in order to cope with continuously increasing large hadron collider luminosity and more demanding requirements on trigger efficiency and performance, various upgrades for the full-trigger system were already deployed and others are foreseen in the next years. Most of the trigger upgrades are based on the state-of-the-art technologies and allow designing more complex trigger menus, increasing processing power and data transfer bandwidth in order to send more trigger candidates, to perform topological selections, and to support new physics studies. In this paper, we describe the design of the first prototype of the barrel interface board, designed around a Xilinx field-programmable gate array, which transfers RPC trigger data to the CTP system; the board supports the optical transmission of trigger data with fixed latency and new trigger algorithms. We discuss the design strategies, the hardware implementation, and the results of the first functional and integration tests.

Longevity studies and Phase 2 electronics upgrade for CMS Cathode Strip Chambers in preparation for HL-LHC

The Cathode Strip Chamber (CSC) is the primary system for muon detection in the CMS endcap region. Starting in 2026 both the instantaneous luminosity and CMS level 1 latency will be increased significantly, which will exceed the design specifications of the CSC electronics. The large integrated particle flux also increases the potential for chamber aging and performance degradation. This paper presents the studies of CSC electronics and CSC longevity performed at the CERN GIF++ facility.

MRPC3b mass production for CBM-TOF and eTOF at STAR

The Compressed Baryonic Matter (CBM) spectrometer aims to study strongly interacting matter under extreme conditions. The key element providing hadron identification at incident energies between 2 and 11AGeV in heavy-ion collisions at the SIS100 accelerator is a Time-of-Flight (TOF) wall covering the polar angular range from 2.5̂–25̂ and full azimuth. CBM is expected to be operational in the year 2024 at the Facility for Anti-proton and Ion Research (FAIR) in Darmstadt, Germany. The existing conceptual design foresees a 120 m2 TOF-wall composed of Multi-gap Resistive Plate Chambers (MRPC) which is subdivided into a high rate region, a middle rate region and a low rate region. The MRPC3b Multistrip-MRPCs, foreseen to be integrated in the low rate region, have to cope with charged particle fluxes up to 1 kHz/cm2 and therefore will be constructed with thin float glass (0.28 mm thickness) as resistive electrode material. In the scope of the FAIR phase 0 program it is planned to install about 36% of the MRPC3b counters in the east endcap region of the STAR experiment at BNL as an upgrade for the Beam Energy Scan campaign (BESII) in 2019/2020.

Design and study of the TPC detector module and prototype for CEPC

The Circular Electron Positron Collider (CEPC) has been proposed as a Higgs/[Formula: see text] factory, which would allow precision measurements of the Higgs boson properties, as well as of [Formula: see text] and [Formula: see text] bosons. The baseline design of CEPC tracking system consists of a vertex detector with three concentric double-sided pixel layers, a high precision (about 100 [Formula: see text]m) large volume time projection chamber (TPC) and a silicon tracker on both barrel and end-cap regions. The tracking system has similar performance requirements to the ILD detector in ILC detectors but without power-pulsing, which leads to significantly additional constrains on detector specifications, especially for the case of machine operating at [Formula: see text]-pole energy region with high luminosity. In this paper, we will give an overview of the CEPC TPC detector, the requirements and challenges for the detector with possible technologies. The on-going R&amp;D activities of the TPC detector module and prototype will also be reported.