Compressed Baryonic Matter Experiment Research Articles

The high count-rate self-triggering Silicon Tracking System of the CBM experiment at FAIR: Design, series assembly, upgrade options

The Compressed Baryonic Matter (CBM) experiment is a stationary target spectrometer with hadron and lepton identification. It is under construction at the Facility for Antiproton and Ion Research (FAIR) that is being realized next to the GSI grounds in Darmstadt, Germany. CBM will investigate QCD matter at highest, up to supernova core-collaps baryonic densities (Ablyazimov et al., 2017). This will be done in collisions of nuclear beams with targets at center of mass energies sNN=2.9–4.9 GeV. Because of the long beam extraction technique employed at FAIR’s SIS100 synchrotron, CBM’s data collection can be based on streaming time-stamped detector data into a compute farm. Event determination and physics analysis are performed there online, allowing for collision rates up to 10 MHz. CBM’s core tracking detector is the Silicon Tracking System, operating 8 tracking stations based on double-sided silicon microstrip sensors and self-triggering front-end electronics in a 1 Tm dipole magnetic field (Heuser et al., 2013).

Toward an environmental friendly operation of the CBM-TOF system

The future fixed target high-rate compressed baryonic matter (CBM) experiment is one of the experimental pillars of the Facility for Antiproton and Ion Research (FAIR) located in Darmstadt/Germany. In order to provide an excellent particle identification (PID) of charged hadrons, the CBM-time-of-flight (TOF) group has developed a concept of a 120 m2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document} large TOF wall with a system time resolution below 80 ps based on multi-gap resistive plate chambers (MRPC). Currently, timing MRPC systems are operated with a gas mixture based on tetrafluoroethane (R134a, C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}F4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}) with additions of few vol% quencher gases, e.g., sulfur hexafluoride (SF6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_6$$\\end{document}) or/and isobutane (i-C4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}H10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_10$$\\end{document}). Unfortunately, these gas mixtures have a high global warming potential (GWP) in the order of 1500, and therefore, strategies to reduce the environmental impact have to be developed. The various possibilities, including studies on eco-friendly gases, and the considered strategy by the CBM-TOF group will be elaborated in this article.

Batch testing and noise rate optimization of MRPC3b for CBM-TOF/STAR-eTOF

The Compressed Baryonic Matter (CBM) experiment is one of the major scientific spectrometers of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. As one of the core sub-systems in CBM experiment for charged hadron identification, the Time-of-Flight (TOF) system is required to have a time resolution better than 80 ps. According to the final state particle flux distribution, the CBM-TOF will be constructed with several types of Multi-gap Resistive Plate Chambers (MRPC). In the outer region of the TOF wall where the particle fluxes are around 1 kHz/cm2, MRPCs with ultra-thin float glass electrodes are considered as a cost effective solution. MRPC3b prototypes have been developed and tested with excellent performance which could meet all the requirements. Before the construction of CBM-TOF, approximately 80 MRPC3bs are assembled for the STAR endcap TOF (STAR-eTOF) upgrade at RHIC as part of the FAIR Phase-0 programs for CBM-TOF which provides a valuable opportunity for detector stability test under high flux environments. This paper will introduce the batch test of the MRPC3bs for STAR-eTOF upgrade. Time resolution of better than 70 ps and efficiency of around 95% are achieved. Notably, during the batch test, it has been observed that the noise rates of the two edge strips in each counter are significantly higher than those of the middle strips. Simulations with Computer Simulation Technology (CST) Studio Suite are carried out and several kinds of MRPC prototypes are designed and tested accordingly. Based on the simulation and test results, the design of the MRPC3b has been further optimized by modify the shape and position of High-Voltage injection pad and increasing the distance between the glass edge and both end strips, resulting in a significant suppression of noise rates in the edge strips.

A Neural-Network-Based Competition between Short-Lived Particle Candidates in the CBM Experiment at FAIR

Fast and efficient algorithms optimized for high performance computers are crucial for the real-time analysis of data in heavy-ion physics experiments. Furthermore, the application of neural networks and other machine learning techniques has become more popular in physics experiments over the last years. For that reason, a fast neural network package called ANN4FLES is developed in C++, which will be optimized to be used on a high performance computer farm for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR, Darmstadt, Germany). This paper describes the first application of ANN4FLES used in the reconstruction chain of the CBM experiment to replace the existing particle competition between Ks-mesons and Λ-hyperons in the KF Particle Finder by a neural network based approach. The raw classification performance of the neural network reaches over 98% on the testing set. Furthermore, it is shown that the background noise was reduced by the neural network-based competition and therefore improved the quality of the physics analysis.

Elliptic flow of identified hadrons in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the PHSD model

We present predictions of elliptic flow (v_2) of identified hadrons at mid-rapidity (|y| < 1.0) in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the Parton Hadron String Dynamics (PHSD) model. The transverse momentum (p_{textrm{T}}) dependence of identified hadron v_2 in minimum bias (0–80%) and three different centrality intervals (0–10%, 10–40%, and 40–80%) are presented. A clear centrality dependence of v_2(p_{textrm{T}}) is observed for particles and anti-particles. We also present the p_{textrm{T}} dependence of v_2 difference ({Delta } v_2) between particles and corresponding anti-particles. A significant difference in v_2 values for baryons and anti-baryons is observed. Constituent quark scaling (NCQ) of v_{2} is investigated in Au+Au collisions. We also present a v_2(p_{textrm{T}}) ratio between the HSD and PHSD modes to explore the effect of hadronic and partonic interactions in the medium. These predictions are useful for interpreting the data measured in the Beam Energy Scan (BES) program at RHIC. They will also be useful for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) and Multi-Purpose Detector (MPD) at the Nuclotron-based Ion Collider facility (NICA).

Neural-Network-Based Quark–Gluon Plasma Trigger for the CBM Experiment at FAIR

Algorithms optimized for high-performance computing, which ensure both speed and accuracy, are crucial for real-time data analysis in heavy-ion physics experiments. The application of neural networks and other machine learning methodologies, which are fast and have high accuracy, in physics experiments has become increasingly popular over recent years. This paper introduces a fast neural network package named ANN4FLES developed in C++, which has been optimized for use on a high-performance computing cluster for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR, Darmstadt, Germany). The use of neural networks for classifying events during heavy-ion collisions in the CBM experiment is under investigation. This paper provides a detailed description of the application of ANN4FLES in identifying collisions where a quark–gluon plasma (QGP) was produced. The methodology detailed here will be used in the development of a QGP trigger for event selection within the First Level Event Selection (FLES) package for the CBM experiment. Fully-connected and convolutional neural networks have been created for the identification of events containing QGP, which are simulated with the Parton–Hadron–String Dynamics (PHSD) microscopic off-shell transport approach, for central Au + Au collisions at an energy of 31.2 A GeV. The results show that the convolutional neural network outperforms the fully-connected networks and achieves over 95% accuracy on the testing dataset.

The compressed baryonic matter (CBM) experiment at FAIR—physics, status and prospects

The Compressed Baryonic Matter (CBM) experiment is one of the major scientific pillars of the Facility for Antiproton and Ion Research (FAIR). The physics programme of CBM is centred around the exploration of the QCD phase diagram and nuclear matter equation-of-state in the region of high baryon densities. The respective rare probes will be accessed by using nucleus-nucleus collisions in the energy range at peak interaction rates of up to 10 MHz and a trigger-less data acquisition scheme. This article reviews CBM physics goals with the experimental observables. The progress and current status (as of January 2022 before sanctions imposed on Russia and suspension of collaboration with Russian institutes) of the comprising detector sub‐systems, including their performance in FAIR Phase‐0 experiments will also be presented.

Development of a water-based cooling system for the Muon Chamber detector system of the CBM experiment

A water-based cooling system is being investigated to meet the cooling requirement of the Gas Electron Multiplier (GEM) based Muon Chamber (MuCh) detector system of the Compressed Baryonic Matter (CBM) experiment at GSI, Germany. The system is based on circulating cold water through the channels inside an aluminium plate. The aluminium plate is attached to a GEM chamber. A feasibility study is conducted on one small and two real-size prototype cooling plates. A microcontroller-based unit has been built and integrated into the system to achieve automatic control and monitoring of temperature on the plate surface. The real-size prototypes have been used in a test beam experiment at the CERN SPS (Super Proton Synchrotron) with the lead beam on a lead target. A setup using three prototype modules has been prepared in the lab for testing in a simulated real-life environment. This paper discusses the working principle, mechanical design, fabrication, and test results of the cooling prototypes in detail.

Evaluation of GBT-FPGA for timing and fast control in CBM experiment

Timing and Fast Control (TFC) system for the Compressed Baryonic Matter (CBM) experiment is being developed with focus on low and deterministic data transmission latency. This helps to minimize data corruption in the free-streaming Data Acquisition (DAQ) system during occasional data bursts caused by the expected beam intensity fluctuations. Proven in latency-optimized experimental data transport applications, the GBT-FPGA core is expected to positively contribute to the TFC system performance. In this work, the core has been integrated as the primary communication interface and its effect on transmission latency and quality of time distribution has been evaluated.

Test and characterisation of STS/MuCh-XYTER and integration with multiple detectors of CBM-MuCh detector systems

Compressed Baryonic Matter (CBM) is a fixed target experiment at the upcoming Facility for Anti-proton and Ion Research in Germany, having collision rates up to 10 MHz. Due to the proximity of the target and secondaries produced in absorbers, Muon Chambers (MuCh) of the CBM experiment will face a very high particle hit rate of up to 400 kHz/cm2 in its first two stations. To cope with these particle rates, a Gas Electron Multiplier (GEM) detector will be used for the first two stations while, due to relatively lower particle rates, the last two stations will use a low resistivity Bakelite Resistive Plate Chamber (RPC) detector. The electronics of these two MuCh detectors need different dynamic ranges.A Silicon Tracking Station (STS) system made of 300 μm thick silicon micro-strip sensors will be installed upstream of the MuCh detector system. The sensors will be read out through multi-line micro-cables with fast electronics. The micro-strip sensors will be double-sided with a stereo angle of 7.5°, a strip width of 58 μm, and strip lengths between 20 and 120 mm requiring high-density readout.To meet the high rate and high density requirements of MuCh and STS, respectively, a specialized 128-channel readout ASIC with a dual-gain feature is designed. This is a highly configurable ASIC with about 30,000 configurable register bits which control various bias and threshold settings of the ASIC. To integrate this ASIC with both the detector systems, detailed testing and characterization of the ASIC are required.Due to the high number of configurable registers and several operating conditions, characterizing this ASIC is very challenging. This paper describes the optimization procedures of several configurable bias parameters in detail and also explains how this ASIC is integrated with both GEM and RPC detectors of the MuCh system.

Optimization of the Ring Imaging Cherenkov Photodetector Shielding Box for Compressed Baryonic Matter Experiment

Optimization of the Ring Imaging Cherenkov Photodetector Shielding Box for Compressed Baryonic Matter Experiment

Prototype design of a timing and fast control system in the CBM experiment

The Compressed Baryonic Matter (CBM) experiment is designed to handle interaction rates of up to 10 MHz and up to 1 TB/s of raw data generated. With triggerless streaming data acquisition in the experiment and beam intensity fluctuations, it is expected that occasional data bursts will surpass bandwidth capabilities of the Data Acquisition System (DAQ) system. In order to preserve integrity of event data, the bandwidth of DAQ must be throttled in an organised way with minimum information loss. The Timing and Fast Control (TFC) system provides a latency-optimised datapath for throttling commands and distributes a system clock together with a global timestamp. This paper describes a prototype design of the system with focus on synchronisation and its evaluation.

Probing Compressed Baryonic Matter

The objective of the compressed baryonic matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, is the investigation of the fundamental properties of strongly interacting matter. Of particular interest for our understanding of compact stellar objects is the determination of the equation-of-state (EOS) at high baryon densities and the exploration of the microscopic degrees-of-freedom under these conditions. The results of these laboratory experiments will complement astronomical observations, which also constrain the high-density EOS. Recent results of QCD-based calculations suggest that a possible first-order chiral phase transition should be observable in heavy-ion collisions at FAIR energies. This article reviews relevant observables from heavy-ion collisions and describes the detector configuration and the physics performance of the CBM experiment.

Machine Learning Application for Λ Hyperon Reconstruction in CBM at FAIR

The Compressed Baryonic Matter experiment at FAIR will investigate the QCD phase diagram in the region of high net-baryon densities. Enhanced production of strange baryons, such as the most abundantly produced Λ hyperons, can signal transition to a new phase of the QCD matter. In this work, the CBM performance for reconstruction of the Λ hyperon via its decay to proton and π− is presented. Decay topology reconstruction is implemented in the Particle-Finder Simple (PFSimple) package with Machine Learning algorithms providing effcient selection of the decays and high signal to background ratio.

Performance of a prototype bakelite RPC at GIF++ using self-triggered electronics for the CBM experiment at FAIR

The Muon Chamber (MuCh) is a sub-system of the Compressed Baryonic Matter (CBM) experiment for the detection of low-mass-vector mesons produced in high energy heavy ion collisions at beam energies ranging from 2 AGeV to 11 AGeV and decaying in the di-muon channel. MuCh consists of a segmented absorber and four detector triplet stations sandwiched between the absorber segments. At the 3rd and 4th stations of MuCh, Resistive Plate Chambers (RPCs) have been conceived for muon tracking. We have tested the performance of a low resistivity bakelite RPC prototype equipped with self-triggered front end electronics (MuCh-XYTER) for the CBM Muon Chamber. A systematic study on the muon detection efficiency and time resolution has been carried out in a high-rate photon background at the Gamma Irradiation Facility (GIF++) at CERN. The details of the measurement setup and the results are presented here.

Dynamical particle ratio fluctuations in Au + Au interaction at E lab = 30 A GeV using transport models

We present a simulation study on the dynamical fluctuations of conserved charges in a baryon-rich environment that is expected to be created in high-energy nucleus–nucleus (AB) collisions. Microscopic transport models like the ultra-relativistic quantum molecular dynamics and a multi-phase transport model are used to generate Au + Au collision events at an incident beam energy of 30 A GeV in the laboratory system. We investigate the centrality and rapidity window size dependence of the event-by-event (e-by-e) fluctuations of the multiplicity ratios of particles belonging to different species. It is observed that e-by-e dynamical fluctuations in the K/π, K/p and π/p ratios diminish with increasing centrality. Our results in this regard indicate that an AB collision can not be viewed as a mere superposition of many incoherent nucleon–nucleon (NN) collisions. Similarly, due to diffusion process the dynamical fluctuations get diluted with increasing window size of rapidity. The simulation results in general could be interpreted in terms of conventional mechanisms of particle production like resonance decays. Our simulation based analysis provides a useful reference baseline to the compressed baryonic matter experiment to be held at the Facility for Antiproton and Ion Research (FAIR).

Development and implementation of a time-based signal generation scheme for the muon chamber simulation of the CBM experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment in the upcoming Facility for Antiproton and Ion Research (FAIR), designed to take data in nuclear collisions at very high interaction rates of up to 10 MHz, will employ a free-streaming data acquisition with self-triggered readout electronics, without any hardware trigger. A simulation framework with a realistic digitization of the detectors in the muon chamber (MuCh) subsystem in CBM has been developed to provide a realistic simulation of the time-stamped data stream. In this article, we describe the implementation of the free-streaming detector simulation and the basic data related effects on the detector with respect to the interaction rate.

Data-Driven Methods for Spectator Symmetry Plane Estimation in CBM Experiment at FAIR

The Compressed Baryonic Matter experiment (CBM) at FAIR aims to study the area of the QCD phase diagram at high net baryon densities and moderate temperatures with collisions of heavy ions at sNN=2.8–4.9 GeV. The anisotropic transverse flow is one of the most important observable phenomena in a study of the properties of matter created in such collisions. Flow measurements require the knowledge of the collision symmetry plane, which can be determined from the deflection of the collision spectators in the plane transverse to the direction of the moving ions. The CBM performance for projectile spectator symmetry plane estimation is studied with GEANT4 Monte Carlo simulations using collisions of gold ions with beam momentum of 12A GeV/c generated with the DCM-QGSM-SMM model. Different data-driven methods to extract the correction factor in flow analysis for the resolution of the spectator symmetry plane estimated with the CBM Projectile Spectator Detector are investigated.

Probing Dense QCD Matter: Muon Measurements with the CBM Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt is designed to investigate the properties of high-density QCD matter with multi-differential measurements of hadrons and leptons, including rare probes such as multi-strange anti-hyperons and charmed particles. The research program covers the study of the high-density equation-of-state of nuclear matter and the exploration of the QCD phase diagram at large baryon chemical potentials, including the search for quark matter and the critical endpoint of a hypothetical 1st order phase transition. The CBM setup comprises detector systems for the identification of charged hadrons, electrons, and muons; for the determination of collision centrality and the orientation of the reaction plane; and a free-streaming data read-out and acquisition system, which allows online reconstruction and selection of events up to reaction rates of 10 MHz. In this article, emphasis is placed on the measurement of muon pairs in Au-Au collisions at FAIR beam energies, which are unique probes used to determine the temperature of the fireball, and hence to search for a caloric curve of QCD matter. Simultaneously, the subthreshold production of charmonium can be studied via its dimuon decay in order to shed light on the microscopic structure of QCD matter at high baryon densities. The CBM setup with focus on dimuon measurements and the results of the corresponding physics performance studies will be presented.

The Compressed Baryonic Matter Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at FAIR aims to study the area of the QCD phase diagram at high net baryon densities and moderate temperatures using heavy-ion collisions. The FAIR accelerator will provide high-intensity heavy-ion beams up to Au ions in the beam momentum range 3.5A-12A GeV/c per nucleon. In order to achieve it's physics goals and to perform multi-differential measurements of rare probes such as multistrange hadrons or hypernuclei, CBM plans to operate at unprecedented peak interaction rates of up to 10 MHz.Following an introduction into the physics program of the CBM, recent developments related to the preparation of the experiment, physics performance studies, and detector components tests within the so-called FAIR PHASE-0 program are discussed. In particular, the status of the mCBM project at GSI, which operated with high-intensity beams for the first time last year and combines various CBM detector subsystems with a common data acquisition system (DAQ), are presented.