1,778 research outputs found
Benchmarking message queue libraries and network technologies to transport large data volume in the ALICE O system
No full textALICE (A Large Ion Collider Experiment) is the heavy-ion detector designed to study the physics of strongly interacting matter and the quark-gluon plasma at the CERN LHC (Large Hadron Collider). ALICE has been successfully collecting physics data of Run 2 since spring 2015. In parallel, preparations for a major upgrade, called O2 (Online-Offline) and scheduled for the Long Shutdown 2 in 2019-2020, are being made. One of the major requirements is the capacity to transport data between so-called FLPs (First Level Processors), equipped with readout cards, and the EPNs (Event Processing Node), performing data aggregation, frame building and partial reconstruction. It is foreseen to have 268 FLPs dispatching data to 1500 EPNs with an average output of 20 Gb/s each. In overall, the O2 processing system will operate at terabits per second of throughput while handling millions of concurrent connections. To meet these requirements, the software and hardware layers of the new system need to be fully evaluated. In order to achieve a high performance to cost ratio three networking technologies (Ethernet, InfiniBand and Omni-Path) were benchmarked on Intel and IBM platforms. The core of the new transport layer will be based on a message queue library that supports push-pull and request-reply communication patterns and multipart messages. ZeroMQ and nanomsg are being evaluated as candidates and were tested in detail over the selected network technologies. This paper describes the benchmark programs and setups that were used during the tests, the significance of tuned kernel parameters, the configuration of network driver and the tuning of multi-core, multi-CPU, and NUMA (Non-Uniform Memory Access) architecture. It presents, compares and comments the final results. Eventually, it indicates the most efficient network technology and message queue library pair and provides an evaluation of the needed CPU and memory resources to handle foreseen traffic
MAD - Monitoring ALICE Dataflow
No full textALICE (A Large Ion Collider Experiment) is the heavy-ion detector designed to study the physics of strongly interacting matter and the quark-gluon plasma at the CERN Large Hadron Collider (LHC). Following a successful Run 1, which ended in February 2013, the ALICE data acquisition (DAQ) entered a consolidation phase to prepare for Run 2 which will start in the beginning of 2015. A new software tool has been developed by the data acquisition project to improve the monitoring of the experiment's dataflow, from the data readout in the DAQ farm up to its shipment to CERN's main computer centre. This software, called ALICE MAD (Monitoring ALICE Dataflow), uses the MonALISA framework as core module to gather, process, aggregate and distribute monitoring values from the different processes running in the distributed DAQ farm. Data are not only pulled from the data sources to MAD but can also be pushed by dedicated data collectors or the data source processes. A large set of monitored metrics (from the backpressure status on the readout links to event counters in each of the DAQ nodes and aggregated data rates for the whole data acquisition) is needed to provide a comprehensive view of the DAQ status. MAD also injects alarms in the Orthos alarm system whenever abnormal conditions are detected. The MAD web-based GUI uses WebSockets to provide dynamic and on-time status displays for the ALICE shift crew. Designed as a widget-based system, MAD supports an easy integration of new visualization blocks and also customization of the information displayed to the shift crew based on the ALICE activities
The ALICE Electronic Logbook
No full textAll major experiments need tools that provide a way to keep a record of the events and activities, both during commissioning and operations. In ALICE (A Large Ion Collider Experiment) at CERN, this task is performed by the Alice Electronic Logbook (eLogbook), a custom-made application developed and maintained by the Data-Acquisition group (DAQ). Started as a statistics repository, the eLogbook has evolved to become not only a fully functional electronic logbook, but also a massive information repository used to store the conditions and statistics of the several online systems. It's currently used by more than 600 users in 30 different countries and it plays an important role in the daily ALICE collaboration activities. This paper will describe the LAMP (Linux, Apache, MySQL and PHP) based architecture of the eLogbook, the database schema and the relevance of the information stored in the eLogbook to the different ALICE actors, not only for near real time procedures but also for long term data-mining and analysis. It will also present the web interface, including the different used technologies, the implemented security measures and the current main features. Finally it will present the roadmap for the future, including a migration to the web 2.0 paradigm, the handling of the database ever-increasing data volume and the deployment of data-mining tools
The New Frontier of the DATA Acquisition Using 1 and 10 Gb/s Ethernet links
No full textALICE [1] (A Large Ion Collider Experiment) is the detector system at the LHC (Large Hadron Collider) optimized for the study of heavy-ion collisions. Its main aim is to study the behavior of strongly interacting matter and the quark gluon plasma. Currently all the information sent by the 18 sub-detectors composing ALICE are read out by DATE [2] (Data Acquisition and Test Environment), the ALICE data acquisition software, using several optical links called DDL [3] (Detector Data Link), each one with a maximum throughput of 200 MB/s. In the last year a commercial transmission link with a throughput of 10 Gb/s has become a reality, with a low price affordable for everyone. The DATE system has been upgraded to also support this technology in addition to the DDL. This contribution will describe the VHDL firmware of a detector readout board, sending data using the UDP protocol and the changes made to the readout [4] part of DATE software to receive information coming from the 1 or 10 Gb/s Ethernet link. It will also describe the relevant details of the test firmware and software and will conclude with the results of the performance tests done at CERN using the new setup
Transverse-momentum and event-shape dependence of D-meson flow harmonics in Pb-Pb collisions at root(S)(NN)=5 . 02 TeV
No full textThe elliptic and triangular flow coefficients v(2) and v(3) of prompt D-0 , D+ , and D*(+) mesons were measured at midrapidity (|y| < 0.8) in Pb-Pb collisions at the centre-of-mass energy per nucleon pair of root(S)(NN) = 5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decays in the transverse momentum interval 1 < p(T) < 36 GeV/c in central (0-10%) and semi-central (30-50%) collisions. Compared to pions, protons, and J/psi mesons, the average D-meson v(n) harmonics are compatible within uncertainties with a mass hierarchy for p(T) less than or similar to 3 GeV/c , and are similar to those of charged pions for higher p(T). The coupling of the charm quark to the light quarks in the underlying medium is further investigated with the application of the event-shape engineering (ESE) technique to the D-meson v(2) and p(T)-differential yields. The D-meson v(2) is correlated with average bulk elliptic flow in both central and semi-central collisions. Within the current precision, the ratios of per-event D meson yields in the ESE-selected and unbiased samples are found to be compatible with unity. All the measurements are found to be reasonably well described by theoretical calculations including the effects of charm-quark transport and the recombination of charm quarks with light quarks in a hydrodynamically expanding medium. (C) 2020 The Author(s). Published by Elsevier B.V
J/ψ elliptic flow in Pb-Pb collisions at TeV
No full textWe report on the first measurement of inclusive J/psi elliptic flow v(2) in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at root s(NN) = 2.76 TeV in the rapidity range 2.5 < y < 4.0. The dependence of the J/psi v(2) on the collision centrality and on the J/psi transverse momentum is studied in the range 0 <= p(T) < 10 GeV/c. For semicentral Pb-Pb collisions at root s(NN) = 2.76 TeV, an indication of nonzero v(2) is observed with a largest measured value of v(2) = 0.116 +/-0.046(stat) +/- 0.029(syst) for J/psi in the transverse momentum range 2 <= p(T) < 4 GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/psi nuclear modification factor and favors the scenario of a significant fraction of J/psi production from charm quarks in a deconfined partonic phase
J/psi elliptic and triangular flow in Pb-Pb collisions at root s(NN)=5.02 TeV
No full textThe inclusive J/psi (v(2)) and triangular (v(3)) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (vertical bar y vertical bar < 0.9) in Pb-Pb collisions at root s(NN) = 5.02TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 mu b(-1) at forward rapidity and 93 mu b(-1) at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum p(T) and collision centrality. At midrapidity, the J psi v(2) is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/psi v(3) with a significance of more than 5 sigma at forward rapidity in the p(T) range 2 < p(T) < 5 GeV/c. The forward rapidity v(2), v(3), and v(3)/v(2) results at low and intermediate p(T) (p(T) < 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher p(T). At low and intermediate p(T), the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high p(T), path-length dependent effects seem to dominate. The J/psi v(2) measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/flow
Anisotropic flow and flow fluctuations of identified hadrons in Pb–Pb collisions at √sNN = 5.02 TeV
No full textThe first measurements of elliptic flow of π ±, K ±, p + p ̄ , KS0 , Λ + Λ ̄ , φ, Ξ −+ Ξ ̄ + , and Ω −+ Ω ̄ + using multiparticle cumulants in Pb–Pb collisions at sNN = 5.02 TeV are resented. Results obtained with two- (v 2{2}) and four-particle cumulants (v 2{4}) are shown as a function of transverse momentum, p T, for various collision centrality intervals. Combining the data for both v 2{2} and v 2{4} also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark–gluon plasma. The characteristic features observed in previous p T-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low p T and the approximate scaling with the number of constituent quarks at intermediate p T, are similarly present in the four-particle correlations and the combinations of v 2{2} and v 2{4}. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide p T range. [Figure not available: see fulltext.]
Systematic studies of correlations between different order flow harmonics in Pb-Pb collisions at root s(NN)=2.76 TeV
No full textThe correlations between event-by-event fluctuations of anisotropic flow harmonic amplitudes have been measured in Pb-Pb collisions at root s(NN) = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The results are reported in terms of multiparticle correlation observables dubbed symmetric cumulants. These observables are robust against biases originating from nonflow effects. The centrality dependence of correlations between the higher order harmonics (the quadrangular v(4) and pentagonal v(5) flow) and the lower order harmonics (the elliptic v(2) and triangular v(3) flow) is presented. The transverse momentum dependences of correlations between v(3) and v(2) and between v(4) and v(2) are also reported. The results are compared to calculations from viscous hydrodynamics and a multiphase transport (AMPT) model calculations. The comparisons to viscous hydrodynamic models demonstrate that the different order harmonic correlations respond differently to the initial conditions and the temperature dependence of the ratio of shear viscosity to entropy density (eta/s). Asmall average value of eta/s is favored independent of the specific choice of initial conditions in the models. The calculations with the AMPT initial conditions yield results closest to the measurements. Correlations among the magnitudes of v(2), v(3), and v(4) show moderate p(T) dependence in midcentral collisions. This might be an indication of possible viscous corrections to the equilibrium distribution at hadronic freeze-out, which might help to understand the possible contribution of bulk viscosity in the hadronic phase of the system. Together with existing measurements of individual flow harmonics, the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions
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