Compressed Baryonic Matter Experiment Research Articles

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.

Performance for proton anisotropic flow measurement of the CBM experiment at FAIR

The Compressed Baryonic Matter experiment (CBM) performance for proton anisotropic flow measurements is studied with Monte-Carlo simulations using collisions of gold ions at lab momentum of 12A GeV/c employing DCM-QGSM-SMM heavy-ion event generator. Realistic procedures are used for centrality estimation with the number of registered tracks and particle identification with information from Time-Of-Flight detector. Variation of directed flow estimates depending on various combinations of PSD modules is used to evaluate possible systematic biases due to collision symmetry plane estimation.

Using multiplicity of produced particles for centrality determination in heavy-ion collisions with the CBM experiment

The evolution of matter created in a heavy-ion collision depends on its initial geometry. Experimentally collision geometry is characterized with centrality. Procedure of centrality determination for the Compressed Baryonic Matter (CBM) experiment at FAIR is presented. Relation between parameters of the collision geometry (such as impact parameter magnitude) and centrality classes is extracted using multiplicity of produced charged particles. The latter is connected to the collision geometry parameters using Monte-Carlo Glauber approach.

Artificial neural network for identification of short-lived particles in the CBM experiment

In high energy particle colliders, detectors record millions of points of data during collision events. Therefore, good data analysis depends on distinguishing collisions which produce particles of interest (signal) from those producing other particles (background). Machine learning algorithms in the current times have become popular and useful as the method of choice for such large scale data analysis. In this work, we propose and implement an artificial neural network architecture to achieve the task of identifying precisely the parent particles from all the candidates arising out of track reconstruction from collision data in the future Compressed Baryonic Matter (CBM) experiment. Our framework performs comparably to the existing computational algorithm for this task even with a simple network architecture.

The FAIR Phase 0 program of the CBM TOF

In order to provide particle identification (PID) of charged hadrons at the future high-rate Compressed Baryonic Matter (CBM) experiment, the TOF group has developed a large-area Time-of-Flight (ToF) wall equipped with Multi-gap Resistive Plate Chambers (MRPC) capable to operate at incident particle fluxes of up to 30 kHz/cm2. Prior to its destined operation at the Facility for Antiproton and Ion Research (FAIR)—starting in 2025—this high-rate timing MRPC technology will be used for physics research at two scientific pillars of the FAIR Phase-0 program: the end-cap TOF upgrade of the STAR experiment at RHIC and the mini-TOF (mTOF) wall of the mini-CBM (mCBM) experiment at Schwerionensynchrotron18 (SIS18). At STAR, the fixed-target program of the Beam Energy Scan II (BES-II) will rely on 108 CBM MRPC detectors for forward PID at trigger rates of up to 2 kHz. At mCBM, high-performance benchmark runs of Lambda-baryon production at top SIS18 energies and CBM design interaction rates of 10 MHz will become feasible with a PID backbone consisting of 25 CBM MRPC detectors. Apart from the physics perspective, these pre-FAIR involvements will help gathering experience in operating the final CBM TOF wall comprising about 1500 MRPC detectors and 110,000 readout channels. The status of the FAIR phase 0 program will be discussed.

The readout system of the CBM Projectile Spectator Detector at FAIR

The Projectile Spectator Detector (PSD) is a sampling lead/scintillator forward hadron calorimeter with transverse and longitudinal segmentation and with MPPC photodetectors light readout. The PSD will be used at the Compressed Baryonic Matter (CBM) experiment at FAIR to measure the nucleus-nucleus collision centrality and orientation of the reaction plane. The CBM experiment will use a free-streaming data acquisition system (DAQ), which requires a coordinated time stamping of data in all sub-systems. To test prototypes of the CBM sub-detectors, front-end electronics (FEE) and readout electronics at high heavy ion beam rates the “mini CBM” (mCBM) installation has been assembled at SIS18 accelerator in GSI, Darmstadt, Germany in the framework of the FAIR Phase-0 program. A single “mini PSD” (mPSD) module has been integrated into the mCBM experiment. Details of the mPSD readout electronics and the first results of the data acquisition, processing and transmission within the common synchronized mCBM data transport system taken during the first beam tests are shown.

Throttling strategies and optimization of the trigger-less streaming DAQ system in the CBM experiment

The Compressed Baryonic Matter experiment (CBM) operating at high heavy-ion interaction rates of up to 10 MHz excludes conventional, latency-limited trigger architectures. Instead, CBM opted for a trigger-less streaming readout. To be able to operate the experiment at highest interaction rates, despite beam intensity fluctuations introduced by the slow extraction of the SIS 100 synchrotron, a time-based throttling mechanism is investigated. To achieve a high number of complete readout events, different throttling strategies are compared and the throttling algorithms and parameters are optimized.

Quality assurance test of the STS-XYTERv2 ASIC for the silicon tracking system of the CBM experiment

The Compressed Baryonic Matter (CBM) Experiment will be one of the major scientific endeavors of the future Facility of Antiproton and Ion Research (FAIR) in Darmstadt. Nuclear collisions at an interaction rate of up to 10 MHz will provide the data for numerous observables, including rare probes with necessary statistical significance. Key to achieve this goal is a fast and radiation hard detector subsystem for particle tracking. In the CBM experiment, the Silicon Tracking System (STS) is the main system for particle tracking. Signal read-out from the 2x1024 channel sensors is based on the self-triggering STS-XYTERv2 ASIC specifically developed for this application. Towards final STS-operation, a down-scaled mini-CBM (mCBM) setup was taken into operation at the SIS18 accelerator at GSI. In this paper, the test measurements of the STS-XYTERv2 asıcs and operational tests performed for quality assurance during the assembly of the mSTS detector modules will be presented and discussed in detail. These measurement procedures will constitute fundamental processes for quality assurance (QA) in the assembly of the roughly 900 STS detector modules.

Probing dense QCD matter in the laboratory—The CBM experiment at FAIR

The ‘Facility for Antiproton and Ion Research’ (FAIR) in Darmstadt will provide unique research opportunities for the investigation of fundamental open questions related to nuclear physics and astrophysics, including the exploration of QCD matter under extreme conditions, which governs the structure and dynamics of cosmic objects and phenomena like neutron stars, supernova explosions, and neutron star mergers. The physics program of the Compressed Baryonic Matter (CBM) experiment is devoted to the production and investigation of dense nuclear matter, with a focus on the high-density equation-of-state (EOS), and signatures for new phases of dense QCD matter. According to the present schedule, the CBM experiment will receive the first beams from the FAIR accelerators in 2025. This article reviews promising observables, outlines the CBM detector system, and presents results of physics performance studies.

Astrophysics in the Laboratory—The CBM Experiment at FAIR

The future “Facility for Antiproton and Ion Research” (FAIR) is an accelerator-based international center for fundamental and applied research, which presently is under construction in Darmstadt, Germany. An important part of the program is devoted to questions related to astrophysics, including the origin of elements in the universe and the properties of strongly interacting matter under extreme conditions, which are relevant for our understanding of the structure of neutron stars and the dynamics of supernova explosions and neutron star mergers. The Compressed Baryonic Matter (CBM) experiment at FAIR is designed to measure promising observables in high-energy heavy-ion collisions, which are expected to be sensitive to the high-density equation-of-state (EOS) of nuclear matter and to new phases of Quantum Chromo Dynamics (QCD) matter at high densities. The CBM physics program, the relevant observables and the experimental setup will be discussed.

Simultaneous muon and reference hadron measurements in the compressed baryonic matter experiment at FAIR

The mission of the Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt is to explore the QCD phase diagram at high net baryon densities likely to exist in the core of neutron stars. The CBM detector system is designed to perform multi-differential measurements of hadrons and leptons in central gold-gold collisions at beam energies between 2 and 11 A GeV with unprecedented precision and statistics. In order to reduce the systematic errors of the lepton measurements, which generally suffer from a large combinatorial background, both electrons and muons will be measured with the same acceptance. Up to now, no di-muon measurements have been performed in heavy-ion collisions at beam energies below 158 A GeV. The main device for electron identification, a Ring Imaging Cherenkov (RICH) detector, can be replaced by a setup comprising hadron absorbers and tracking detectors for muon measurements. In order to obtain a complete picture of the reaction, it is important to measure simultaneously leptons and hadrons. This requirement is fulfilled for the RICH, which has a low material budget, and only little affects the trajectories of hadrons on their way to the Time-of-Flight (TOF) detector. In contrast, the simultaneous measurement of muons and hadrons within the same experimental acceptance poses a substantial challenge. This article reviews the simulated performance of the CBM experiment for muon identification, together with the possibility of simultaneous hadron measurements.

Status of the Compressed Baryonic Matter experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment will investigate high-energy heavy-ion collisions at the international Facility for Antiproton and Ion Research (FAIR), which is under construction in Darmstadt, Germany. The CBM research program is focused on the exploration of QCD matter at neutron star core densities, such as study of the equation-of-state and the search for phase transitions. Key experimental observables include (multi-) strange (anti-) particles, electron-positron pairs and dimuons, particle correlations and fluctuations, and hyper-nuclei. In order to measure these diagnostic probes multi-differentially with unprecedented precision, the CBM detector and data acquisition systems are designed to run at reaction rates up to 10 MHz. This requires the development of fast and radiation hard detectors and readout electronics for track reconstruction, electron and muon identification, time-of-flight (TOF) determination and event characterization. The data are read-out by ultra-fast, radiation-tolerant, and free-streaming front-end electronics, and then transferred via radiation-hard data aggregation units and high-speed optical connections to a high-performance computing center. A fast and highly parallelized software will perform online track reconstruction, particle identification and event analysis. The components of the CBM experimental setup will be discussed and results of physics performance studies will be presented.

Event Reconstruction in the Tracking System of the CBM Experiment

The Compressed Baryonic Matter experiment (CBM) will investigate strongly interacting matter at high net-baryon densities by measuring nucleus-nucleus collisions at the FAIR research centre in Darmstadt, Germany. Its ambitious aim is to measure at very high interaction rates, unprecedented in the field of experimental heavy-ion physics so far. This goal will be reached with fast and radiation-hard detectors, self-triggered read-out electronics and streaming data acquisition without any hardware trigger. Collision events will be reconstructed and selected in real-time exclusively in software. This puts severe requirements to the algorithms for event reconstruction and their implementation. We will discuss some facets of our approaches to event reconstruction in the main tracking device of CBM, the Silicon Tracking System, covering local reconstruction (cluster and hit finding) as well as track finding and event definition.

Exploring Cosmic Matter in the Laboratory—The Compressed Baryonic Matter Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment is one of four scientific pillars of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. In collisions between heavy nuclei at FAIR energies, it is expected that the matter in the reaction zone is compressed to more than five times saturation density, corresponding to the density in the core of a massive neutron star. This offers the unique opportunity to study in the laboratory the high-density equation-of-state (EOS) of nuclear matter, and to search for new phases of Quantum Chromo Dynamics (QCD) matter at large baryon-chemical potentials. Promising experimental observables sensitive to the EOS and to possible phase transitions will be discussed, together with a brief description of the CBM experiment.

Scheduling data streams for low latency and high throughput on a Cray XC40 using Libfabric

SummaryAchieving efficient many‐to‐many communication on a given network topology is a challenging task when many data streams from different sources have to be scattered concurrently to many destinations with low variance in arrival times. In such scenarios, it is critical to saturate but not to congest the bisectional bandwidth of the network topology in order to achieve a good aggregate throughput. When there are many concurrent point‐to‐point connections, the communication pattern needs to be dynamically scheduled in a fine‐grained manner to avoid network congestion (links, switches), overload in the node's incoming links, and receive buffer overflow. Motivated by the use case of the Compressed Baryonic Matter experiment (CBM), we study the performance and variance of such communication patterns on a Cray XC40 with different routing schemes and scheduling approaches. We present a distributed Data Flow Scheduler (DFS) that reduces the variance of arrival times from all sources at least 30 times and increases the achieved aggregate bandwidth by up to 50%.

Track based alignment procedure for the CBM silicon tracking detector

The CBM (Compressed Baryonic Matter) experiment at FAIR is being designed for the study of the QCD phase diagram in the region of the high baryon chemical potential at relatively moderate temperatures. The Silicon Tracking System (STS) is the central detector for momentum reconstruction of the produced charged particles in the CBM experiment. It consists of 8 layers of altogether ∼ 900 double sided silicon micro strip sensors. Limited mechanical precision(> 100μm) during the mounting, temperature differences during the experiment, influence of the applied magnetic field result in misalignment to the detector component positions. Therefore, the intrinsic spatial resolution(∼ 20μm) of the detector components has to be recovered by a track based alignment method. In this conference paper, the current status of implementation of the alignment algorithm is presented. For this work, the GBL (General broken line) track refit model is employed to create the necessary input data structure to provide the input to the standalone PEDE part of the χ2 minimization based MILLEPEDE II alignment algorithm.

Prototype single-ended and pseudo-differential charge processing circuit for micro-strip silicon and gaseous sensors read-out

Detector read-out electronics for Physics Experiments as for example Compressed Baryonic Matter experiment at FAIR, Darmstadt, Germany, should meet tight requirements concerning noise (ENC < 1000 e− rms to guarantee event reconstruction), power consumption (< 10 mW/channel) and average input hit frequency of 250 kHit/s/channel. The ICs design should take into account not only the charge processing parameters but also the impact of the environmental and system-level conditions like radiation, noisy power supply, and temperature to ensure reliable and stable operation during an experiment in a system built with tens of thousands of devices. The operation with gaseous detectors requires particularly effective protection of the inputs against electrostatic discharge. The ESD protection circuit (in particular based on MOS transistors), together with the sensor itself, or AC-coupling capacitors (after irradiation) can be however a source of additional leakage current flowing into the first stage of charge processing chain and affecting the performance. The read-out electronics (in particular first stage—charge sensitive amplifier, CSA) and detector-related noise can be mitigated using proper filtration and signal shaping. However, noise introduced by external sources, like power supply interference, can not be limited only via proper shaping and filtration. When LC filtering is not possible (due to high magnetic fields), it may be beneficial to use differential or pseudo-differential signal processing. The purpose of this work was to test several ideas to improve noise performance and to make the architecture of charge processing chain configurable to better adapt to different target radiation imaging applications. The ASIC comprises four single-ended and four pseudo-differential signal processing channels. In both types of channels configurable slow shaper configuration is used—it is switchable CR-RC2 type shaper and complex conjugate poles 3rd order shaper. CSA feedback in single-ended architecture can be selected between MOS transistor working in a linear region and double-polarity Krummenacher circuit for leakage current compensation capability. The chip was designed and fabricated in Q4 2018 using 180 nm process. Front-end single-ended and differential channels occupy the area from 950 × 60 μm2 up to 1150 × 125 μm2 and consume 5 mW up to 12 mW of power respectively. The work presents design and measurements results.

The Silicon Tracking System of the CBM Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) aims to study the properties of nuclear matter at high net-baryon densities and moderate temperatures.The Silicon Tracking System (STS) is the key detector to reconstruct with a high efficiency up to 1000 charged particle trajectories created in heavy-ion collisions at interaction rates of up to 10 MHz. It will determine the momentum of the particles with a momentum resolution Δp/p ≈ 1-2% which requires ultra-low detector material budget of 0.3-1% X0 per layer. The detector comprise eight layers of double-sided silicon micro-strip sensors and will be placed inside the 1 Tm superconducting magnet which limits the space available, which in turn requires advanced cooling approaches and mechanical design with precise tracking layers alignment. The micro-strip sensors have to be radiation hard and checked for their quality optically and electrically before the assembly.This contribution gives an overview of the STS and presents the status of its component quality control and assembly procedures.

Operating large size GEM detectors using a novel optocoupler based biasing scheme for the Muon Chamber system of CBM experiment

An assembly of large area (∼2000 cm2) triple GEM detector modules will be used for the first two stations of Muon Chamber (MUCH) system of Compressed Baryonic Matter (CBM) experiment at FAIR. Each GEM foil has its top surface segmented into 24 divisions. A novel HV distribution schematic has been implemented to power the individual segments. This design based on optocouplers is not only cost-effective but also has the capability to isolate the faulty segments if required, during the process of data taking. A large size prototype based on this layout was designed and fabricated. The performance of such a prototype has been discussed. Radiation and stability tests of the optocouplers with regards to CBM requirements (a ten-year integrated dose of ∼1012neq/cm2 for neutrons and ∼30 krad for Gammas) has been reported.