The D meson yields as a function of charged-particle multiplicity in pp collisions at s=7 TeV and in p-Pb collisions at sNN=5.02 TeV are presented. The measurement of the yields of electrons from ...heavy-flavour hadron decays as a function of charged-particle multiplicity in p-Pb collisions at sNN=5.02 TeV are shown as well. The measurement of azimuthal correlations of prompt D mesons and charged hadrons in pp collisions at s=7 TeV and in p-Pb collisions at sNN=5.02 TeV are also presented. The results are compared with expectations from models.
A cloud-based Virtual Analysis Facility (VAF) for the ALICE experiment at the LHC has been deployed in Bari. Similar facilities are currently running in other Italian sites with the aim to create a ...federation of interoperating farms able to provide their computing resources for interactive distributed analysis. The use of cloud technology, along with elastic provisioning of computing resources as an alternative to the grid for running data intensive analyses, is the main challenge of these facilities. One of the crucial aspects of the user-driven analysis execution is the data access. A local storage facility has the disadvantage that the stored data can be accessed only locally, i.e. from within the single VAF. To overcome such a limitation a federated infrastructure, which provides full access to all the data belonging to the federation independently from the site where they are stored, has been set up. The federation architecture exploits both cloud computing and XRootD technologies, in order to provide a dynamic, easy-to-use and well performing solution for data handling. It should allow the users to store the files and efficiently retrieve the data, since it implements a dynamic distributed cache among many datacenters in Italy connected to one another through the high-bandwidth national network. Details on the preliminary architecture implementation and performance studies are discussed.
The present work aims at optimizing the use of computing resources available at the grid Italian Tier-2 sites of the ALICE experiment at CERN LHC by making them accessible to interactive distributed ...analysis, thanks to modern solutions based on cloud computing. The scalability and elasticity of the computing resources via dynamic ("on-demand") provisioning is essentially limited by the size of the computing site, reaching the theoretical optimum only in the asymptotic case of infinite resources. The main challenge of the project is to overcome this limitation by federating different sites through a distributed cloud facility. Storage capacities of the participating sites are seen as a single federated storage area, preventing the need of mirroring data across them: high data access efficiency is guaranteed by location-aware analysis software and storage interfaces, in a transparent way from an end-user perspective. Moreover, the interactive analysis on the federated cloud reduces the execution time with respect to grid batch jobs. The tests of the investigated solutions for both cloud computing and distributed storage on wide area network will be presented.
In 2012, 14 Italian institutions participating in LHC Experiments won a grant from the Italian Ministry of Research (MIUR), with the aim of optimising analysis activities, and in general the Tier2 ...Tier3 infrastructure. We report on the activities being researched upon, on the considerable improvement in the ease of access to resources by physicists, also those with no specific computing interests. We focused on items like distributed storage federations, access to batch-like facilities, provisioning of user interfaces on demand and cloud systems. R&D on next-generation databases, distributed analysis interfaces, and new computing architectures was also carried on. The project, ending in the first months of 2016, will produce a white paper with recommendations on best practices for data-analysis support by computing centers.
ALICE at the CERN LHC will investigate the physics of strongly interacting matter at extreme energy densities where the formation of the Quark Gluon Plasma is expected. Its properties can be studied ...from observations like the production of mesons with charm and beauty quarks. These signals have to be studied as a function of energy density, which is determined by the centrality of collisions. One of the physics observables that is closely related with the centrality of the collision is the number of spectator nucleons that can be measured by the Zero Degree Calorimeters (ZDC). Having a direct geometric interpretation allows to extract the impact parameter with minimal model assumptions. This paper describes the readout system of the ZDC. The ZDC readout consists of a VME system with a ZDC Readout Card, a VME Processor, Discriminators, a ZDC Trigger Card, scalers, QDCs and TDCs. The system was successfully tested during the 2009 ALICE data taking and is currently operational at the LHC.
The Zero Degree Calorimeters (ZDCs) for the ALICE experiment will measure the energy of the spectator nucleons in heavy ion collisions at the CERN LHC. Since all the spectator nucleons have the same ...energy, the calorimeter reponse is proportional to their umber providing a direct information on the centrality of the collision. Two sets of ZDCs are located at opposite sides with respect to the interaction point (I), 116 m away from it Each set consists of a neutron (ZN) calorimeter, placed between the two beam pipes, an a proton (ZP) calorimeter, posioned externally to the outgoing beam pipe. The ZDCs spaghetti calorimeters, which detect the Cherenkov light produced by the shower particle in silica optical fibers embedded in a dense absorber. In summer 2007 the ZN and ZP calorimeters have been placed on a movable platform and then installed in the LHC tunnel. The results of the commissioning studies and in particular the solutions adopted to control the stability of the PMTs response will be shown: light injection with a larser diode and cosmic rays. The foreseen calibration with e.m. dissociation event in Pb-Pb collisions will also be disussed. Finally the it meaurements carried out during the commissining in the LHC tunnel will be presentend.
Commissioning of the ALICE muon spectrometer trigger at LHC Ahn, S.; Arnaldi, R.; Baek, Y. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2012, Letnik:
661
Journal Article
Recenzirano
ALICE (a large ion collider experiment) is the LHC experiment dedicated to the study of ultra-relativistic heavy ion collisions. The ALICE muon spectrometer covers a large range in pseudo-rapidity ...and is designed to study quarkonia and heavy flavours decaying into (di-)muons. The high particle multiplicities environment in such collisions require a specific, fast and efficient trigger system, the muon trigger. It consists of four planes of RPC detectors, covering an area of 36
m
2 each, 21k front-end channels and a fast-decision electronics. The muon trigger is designed to reconstruct (muon) tracks and deliver a trigger signal each 25
ns (40
MHz) with a total latency of 800
ns. The hit position on the RPC is measured in two orthogonal directions with an accuracy of about 1
cm. The performance measured with the first p–p collisions at
(
s
)
=
900
GeV
carried out in December 2009 is reported.
ALICE is the dedicated heavy-ion experiment at the LHC collider. It will also collect proton-proton and proton-nucleus data as reference to study the onset of the transition to the Quark-Gluon Plasma ...state predicted by the Standard Model. The ALICE experimental setup essentially consists of a central barrel for particle tracking and identification, a forward spectrometer for muon detection and forward rapidity detectors to provide the triggers and to characterize the event. Among the forward detectors, the Zero Degree Calorimeter (ZDC) will measure the centrality in nucleus-nucleus and in proton-nucleus collisions. In A-A interactions the observable most directly correlated to the geometry of the collision is the energy carried forward by non interacting (spectator) nucleons. In p-A collisions the centrality evaluation relies instead on the detection of the so called “slow” nucleons emitted by the nucleus. In both cases the simulation results show that the ZDC can be used to trigger on centrality with good accuracy over the whole centrality range. The ZDC will also provide an estimate of the beam luminosity in A-A collisions by measuring the rate of neutron emission in electromagnetic dissociation processes.
A group of Early-Career Researchers (ECRs) has been given a mandate from the European Committee for Future Accelerators (ECFA) to debate the topics of the current European Strategy Update (ESU) for ...Particle Physics and to summarise the outcome in a brief document 1. A full-day debate with 180 delegates was held at CERN, followed by a survey collecting quantitative input. During the debate, the ECRs discussed future colliders in terms of the physics prospects, their implications for accelerator and detector technology as well as computing and software. The discussion was organised into several topic areas. From these areas two common themes were particularly highlighted by the ECRs: sociological and human aspects; and issues of the environmental impact and sustainability of our research.
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