The ALICE experiment uses an optical read-out protocol called Detector Data Link (DDL) to connect the detectors with the computing clusters of Data Acquisition (DAQ) and High-Level Trigger (HLT). The ...interfaces of the clusters to these optical links are realized with FPGA-based PCI-Express boards. The High-Level Trigger is a computing cluster dedicated to the online reconstruction and compression of experimental data. It uses a combination of CPU, GPU and FPGA processing. For Run 2, the HLT has replaced all of its previous interface boards with the Common Read-Out Receiver Card (C-RORC) to enable read-out of detectors at high link rates and to extend the pre-processing capabilities of the cluster. The new hardware also comes with an increased link density that reduces the number of boards required. A modular firmware approach allows different processing and transport tasks to be built from the same source tree. A hardware pre-processing core includes cluster finding already in the C-RORC firmware. State of the art interfaces and memory allocation schemes enable a transparent integration of the C-RORC into the existing HLT software infrastructure. Common cluster management and monitoring frameworks are used to also handle C-RORC metrics. The C-RORC is in use in the clusters of ALICE DAQ and HLT since the start of LHC Run 2.
The ALICE High-Level Trigger (HLT) has a large high-performance computing cluster at CERN whose main objective is to perform real-time analysis on the data generated by the ALICE experiment and scale ...it down to at-most 4GB/sec - which is the current maximum mass-storage bandwidth available. Data-flow in this cluster is controlled by a custom designed software framework. It consists of a set of components which can communicate with each other via a common control interface. The software framework also supports the creation of different configurations based on the detectors participating in the HLT. These configurations define a logical data processing “chain” of detector data-analysis components. Data flows through this software chain in a pipelined fashion so that several events can be processed at the same time. An instance of such a chain can run and manage a few thousand physics analysis and data-flow components. The HLT software and the configuration scheme used in the 2011 heavy-ion runs of ALICE, has been discussed in this contribution.
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Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high ...temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (
s
N
N
=
2.7--4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (
μ
B
>
500
MeV), effects of chiral symmetry, and the equation of state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2024, in the context of the worldwide efforts to explore high-density QCD matter.
The ALICE High Level Trigger comprises a large computing cluster, dedicated interfaces and software applications. It allows on-line event reconstruction of the full data stream of the ALICE ...experiment at up to 25 GByte/s. The commissioning campaign has passed an important phase since the startup of the Large Hadron Collider in November 2009. The system has been transferred into continuous operation with focus on the event reconstruction and first simple trigger applications. The paper reports for the first time on the achieved event reconstruction performance in the ALICE central barrel region.
ALICE HLT High Speed Tracking on GPU Gorbunov, S.; Rohr, D.; Aamodt, K. ...
IEEE transactions on nuclear science,
08/2011, Letnik:
58, Številka:
4
Journal Article
Recenzirano
The on-line event reconstruction in ALICE is performed by the High Level Trigger, which should process up to 2000 events per second in proton-proton collisions and up to 300 central events per second ...in heavy-ion collisions, corresponding to an input data stream of 30 GB/s. In order to fulfill the time requirements, a fast on-line tracker has been developed. The algorithm combines a Cellular Automaton method being used for a fast pattern recognition and the Kalman Filter method for fitting of found trajectories and for the final track selection. The tracker was adapted to run on Graphics Processing Units (GPU) using the NVIDIA Compute Unified Device Architecture (CUDA) framework. The implementation of the algorithm had to be adjusted at many points to allow for an efficient usage of the graphics cards. In particular, achieving a good overall workload for many processor cores, efficient transfer to and from the GPU, as well as optimized utilization of the different memories the GPU offers turned out to be critical. To cope with these problems a dynamic scheduler was introduced, which redistributes the workload among the processor cores. Additionally a pipeline was implemented so that the tracking on the GPU, the initialization and the output processed by the CPU, as well as the DMA transfer can overlap. The GPU tracking algorithm significantly outperforms the CPU version for large events while it entirely maintains its efficiency.
The azimuthal correlations of D mesons with charged particles were measured with the ALICE apparatus in pp collisions at Formula: see text and p-Pb collisions at Formula: see text at the Large Hadron ...Collider. Formula: see text, Formula: see text, and Formula: see text mesons and their charge conjugates with transverse momentum Formula: see text and rapidity in the nucleon-nucleon centre-of-mass system Formula: see text (pp collisions) and Formula: see text (p-Pb collisions) were correlated to charged particles with Formula: see text. The yield of charged particles in the correlation peak induced by the jet containing the D meson and the peak width are compatible within uncertainties in the two collision systems. The data are described within uncertainties by Monte-Carlo simulations based on PYTHIA, POWHEG, and EPOS 3 event generators.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The azimuthal correlations of D mesons with charged particles were measured with the ALICE apparatus in pp collisions at s=7TeV and p–Pb collisions at sNN=5.02TeV at the Large Hadron Collider. D0, ...D+, and D∗+ mesons and their charge conjugates with transverse momentum 3<pT<16GeV/c and rapidity in the nucleon-nucleon centre-of-mass system |ycms|<0.5 (pp collisions) and -0.96<ycms<0.04 (p–Pb collisions) were correlated to charged particles with pT>0.3GeV/c. The yield of charged particles in the correlation peak induced by the jet containing the D meson and the peak width are compatible within uncertainties in the two collision systems. The data are described within uncertainties by Monte-Carlo simulations based on PYTHIA, POWHEG, and EPOS 3 event generators.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Measurements of charged jet production as a function of centrality are presented for p-Pb collisions recorded at Formula: see text TeV with the ALICE detector. Centrality classes are determined via ...the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon-nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-Formula: see text algorithm for resolution parameters Formula: see text and Formula: see text in the transverse momentum range 20 to 120 GeV/
. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p-Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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