-
D. Adamová,
G. Agakichiev,
A. Andronic,
D. Antończyk,
H. Appelshäuser,
V. Belaga,
J. Bielciková,
P. Braun-Munzinger,
O. Busch,
A. Cherlin, [......],
J. Stachel,
M. Sumbera, H. Tilsner,
I. Tserruya,
G. Tsiledakis,
J. P. Wessels,
T. Wienold,
J. P. Wurm,
S. Yurevich,
V. Yurevich
[show abstract]
[hide abstract]
ABSTRACT: Differential elliptic flow spectra v2(pT) of \pi-, K0short, p, \Lambda have
been measured at \sqrt(s NN)= 17.3 GeV around midrapidity by the
CERN-CERES/NA45 experiment in mid-central Pb+Au collisions (10% of
\sigma(geo)). The pT range extends from about 0.1 GeV/c (0.55 GeV/c for
\Lambda) to more than 2 GeV/c. Protons below 0.4 GeV/c are directly identified
by dE/dx. At higher pT, proton elliptic flow v2(pT) is derived as a
constituent, besides \pi+ and K+, of the elliptic flow of positive pion
candidates. The retrieval requires additional inputs: (i) of the particle
composition, and (ii) of v2(pT) of positive pions. For (i), particle ratios
obtained by NA49 were adapted to CERES conditions; for (ii), the measured
v2(pT) of negative pions is substituted, assuming \pi+ and \pi- elliptic flow
magnitudes to be sufficiently close. The v2(pT) spectra are compared to
ideal-hydrodynamics calculations. In synopsis of the series \pi- - K0short - p
- \Lambda, flow magnitudes are seen to fall with decreasing pT progressively
even below hydro calculations with early kinetic freeze-out (Tf= 160 MeV)
leaving not much time for hadronic evolution. The proton v2(pT) data show a
downward swing towards low pT with excursions into negative v2 values. The
pion-flow isospin asymmetry observed recently by STAR at RHIC, invalidating in
principle our working assumption, is found in its impact on proton flow
bracketed from above by the direct proton flow data, and not to alter any of
our conclusions. Results are discussed in perspective of recent viscous
dynamics studies which focus on late hadronic stages.
05/2012;
-
D. Adamová,
G. Agakichiev,
H. Appelshäuser,
V. Belaga,
P. Braun-Munzinger,
A. Cherlin,
S. Damjanović,
T. Dietel,
L. Dietrich,
A. Drees, [......],
M. Sumbera, H. Tilsner,
I. Tserruya,
J. P. Wessels,
T. Wienold,
B. Windelband,
J. P. Wurm,
W. Xie,
S. Yurevich,
V. Yurevich
[show abstract]
[hide abstract]
ABSTRACT: The CERES/NA45 experiment at the CERN SPS has previously measurede
+
e
- pair production in 160 A.GeV Pb-Au collisions. In the mass regionm > 02 GeV/c2, an enhancement of 2.7±04(stat.)±0.5(syst.) compared to the expectation from known hadronic decay sources was observed. In
the 40 A.GeV data taken in 1999, an enhancement is again found; a preliminary analysis gives an even larger value of 50 ±13(stat.).
The results are compared to theoretical model calculations based on π+π- annihilation with a modified ρ-propagator; they may be related to chiral symmetry restoration.
Pramana 04/2012; 60(5):1067-1072. · 0.57 Impact Factor
-
D. Adamová,
G. Agakichiev,
A. Andronic,
D. Antończyk,
H. Appelshäuser,
V. Belaga,
J. Bielčíková,
P. Braun-Munzinger,
O. Busch,
A. Cherlin, [......],
R. Soualah,
J. Stachel,
M. Šumbera, H. Tilsner,
I. Tserruya,
G. Tsiledakis,
J. P. Wessels,
J. P. Wurm,
S. Yurevich,
V. Yurevich
Nuclear Physics A 10/2009; 830:945-945. · 1.54 Impact Factor
-
Ceres Collaboration,
D. Adamova,
G. Agakichiev,
A. Andronic,
D. Antonczyk,
H. Appelshaeuser,
V. Belaga,
J. Bielcikova,
P. Braun-Munzinger,
O. Busch, [......],
J. Stachel,
M. Sumbera, H. Tilsner,
I Tserruya,
G. Tsiledakis,
J. P. Wessels,
T. Wienold,
J P Wurm,
S. Yurevich,
V. Yurevich
[show abstract]
[hide abstract]
ABSTRACT: We present results of a two-pion correlation analysis performed with the Au+Pb collision data collected by the upgraded CERES experiment in the fall of 2000. The analysis was done in bins of the reaction centrality and the pion azimuthal emission angle with respect to the reaction plane. The pion source, deduced from the data, is slightly elongated in the direction perpendicular to the reaction plane, similarly as was observed at the AGS and at RHIC. Comment: 5 pages, 2 figures
05/2008;
-
B. Becker,
S. Chattopadhyay,
C. Cicalo,
J. Cleymans,
G. de Vaux,
R.W. Fearick,
V. Lindenstruth,
M. Richter,
D. Rohrich,
F. Staley,
T.M. Steinbeck,
A. Szostak, H. Tilsner,
R. Weis,
Z.Z. Vilakazi
[show abstract]
[hide abstract]
ABSTRACT: The High Level Trigger (HLT) system of the ALICE experiment is an online event filter and trigger system designed for input bandwidths of up to 25 GB/s at event rates of up to 1 kHz. The system is designed as a scalable PC cluster, implementing several hundred nodes. The transport of data in the system is handled by an object-oriented data flow framework operating on the basis of the publisher-subscriber principle, being designed fully pipelined with lowest processing overhead and communication latency in the cluster. In this paper, we report the latest measurements where this framework has been operated on five different sites over a global north-south link extending more than 10,000 km, processing a ldquoreal-timerdquo data flow.
IEEE Transactions on Nuclear Science 05/2008; · 1.45 Impact Factor
-
B Becker,
S Chattopadhyay,
C. Cicalo J. Cleymans,
G. de Vaux,
R.W. Fearick,
V. Lindenstruth,
M Richter,
D. Rorich,
F. Staley,
T.M. Steinbeck,
A. Szostak, H. Tilsner,
R. Weis,
Z.Z. Vilakazi
[show abstract]
[hide abstract]
ABSTRACT: The High Level Trigger (HLT) system of the ALICE experiment is an online
event filter and trigger system designed for input bandwidths of up to 25 GB/s
at event rates of up to 1 kHz. The system is designed as a scalable PC cluster,
implementing several hundred nodes. The transport of data in the system is
handled by an object-oriented data flow framework operating on the basis of the
publisher-subscriber principle, being designed fully pipelined with lowest
processing overhead and communication latency in the cluster. In this paper, we
report the latest measurements where this framework has been operated on five
different sites over a global north-south link extending more than 10,000 km,
processing a ``real-time'' data flow.
01/2008;
-
M. Richter,
J. Alme,
T. Alt,
S. Bablok,
R. Campagnolo,
U. Frankenfeld,
C.G. Gutierrez,
R. Keidel,
Ch. Kofler,
T. Krawutschke,
D. Larsen,
V. Lindenstruth,
B. Mota,
L. Musa,
K. Roed,
D. Rohrich,
M.R. Stockmeier, H. Tilsner
[show abstract]
[hide abstract]
ABSTRACT: The ALICE detector is a dedicated heavy-ion detector currently built at the Large Hadron Collider (LHC) at CERN. The detector control system (DCS) covers the task of controlling, configuring and monitoring the detector. One sub-system is the control system for the Front-end electronics of the time projection chamber (TPC). It controls in total 216 readout systems with 4356 Front-End Cards serving roughly 560 000 channels. The system consists of a large number of distributed nodes in a layer-structured hierarchy. The low-level node controlling the Front-end electronics is an embedded computer system, the DCS board, which provides the opportunity to run a light-weight Linux system on the card. The board interfaces to the Front-end electronics via a dedicated hardware interface and connects to the higher DCS-layers via the DIM communication framework over Ethernet. Since the experiment will be running in a radiation environment, fault tolerance, error correction and system stability in general are major concerns. Already the low level devices carry out intelligent error handling and act automatically upon several conditions. This paper presents the architecture of the system, the application of the DCS board and experiences from integration tests.
IEEE Transactions on Nuclear Science 07/2006; · 1.45 Impact Factor
-
T. Alt,
H. Appelshauser,
S. Bablok,
B. Becker,
S. Chattopadhyay,
C. Cheshkov,
C. Cicalo,
J. Cleymans,
R.W. Fearick,
H. Helstrup, [......],
T. Steinbeck,
A. Szostak, H. Tilsner,
K. Ullaland,
G. de Vaux,
A. Vestbo,
T. Vik,
Z.Z. Vilakazi,
A. Wiebalck,
G. vrebekk
[show abstract]
[hide abstract]
ABSTRACT: The ALICE High Level Trigger combines and processes the full information from all major detectors in a large computer cluster. Data rate reduction is achieved by reducing the event rate by selecting interesting events (software trigger) and by reducing the event size by selecting sub-events and by advanced data compression. Reconstruction chains for the barrel detectors and the forward muon spectrometer have been benchmarked. The HLT receives a replica of the raw data via the standard ALICE DDL link into a custom PCI receiver card (HLT-RORC). These boards also provide a FPGA co-processor for data-intensive tasks of pattern recognition. Some of the pattern recognition algorithms (cluster finder, Hough transformation) have been re-designed in VHDL to be executed in the Virtex-4 FPGA on the HLT-RORC. HLT prototypes were operated during the beam tests of the TPC and TRD detectors. The input and output interfaces to DAQ and the data flow inside of HLT were successfully tested. A full-scale prototype of the dimuon-HLT achieved the expected data flow performance. This system was finally embedded in a GRID-like system of several distributed clusters demonstrating the scalability and fault-tolerance of the HLT.
IEEE Transactions on Nuclear Science 07/2006; · 1.45 Impact Factor
-
D Adamová,
G Agakichiev,
D Antończyk,
H Appelshäuser,
V Belaga,
J Bielcíková,
P Braun-Munzinger,
O Busch,
A Cherlin,
S Damjanovic, [......],
J Stachel,
M Sumbera, H Tilsner,
I Tserruya,
G Tsiledakis,
J P Wessels,
T Wienold,
J P Wurm,
S Yurevich,
V Yurevich
[show abstract]
[hide abstract]
ABSTRACT: We report on results of a measurement of meson production in central Pb-Au collisions at E(lab) = 158A GeV. For the first time in the history of high energy heavy-ion collisions, phi mesons were reconstructed both in the K+K- and the dilepton decay channels in the same experiment. This measurement yields rapidity densities near midrapidity, from the two decay channels, of 2.05 +/- 0.14(stat) +/- 0.25(syst) and 2.04 +/- 0.49(stat) +/- 0.32(syst), respectively. The shape of the measured transverse momentum spectrum is also in close agreement in both decay channels. The data rule out a possible enhancement of the phi yield in the leptonic over the hadronic decay channel of a factor 1.6 or larger at the 95% C.L. This rules out the discrepancy reported in the literature between measurements of the hadronic and dimuon decay channels by two different experiments.
Physical Review Letters 05/2006; 96(15):152301. · 7.37 Impact Factor
-
T. Alt,
V. Lindenstruth,
T. Steinbeck, H. Tilsner,
A. Wiebalck,
H. Appelshauser,
C. Loizides,
B Becker,
J. Cleymans,
G. de Vaux, [......],
C Cheshkov,
C. Cicalo,
H. Helstrup,
M Richter,
D. Rohrich,
K. Ullaland,
A. Vestbo,
B. Skaali,
T. Vik,
F. Staley
[show abstract]
[hide abstract]
ABSTRACT: The ALICE high level trigger combines and processes the full information from all major detectors in a large computer cluster. Data rate reduction is achieved by reducing the event rate by selecting interesting events (software trigger) and by reducing the event size by selecting sub-events and by advanced data compression. Reconstruction chains for the barrel detectors and the forward muon spectrometer have been benchmarked. The HLT receives a replica of the raw data via the standard ALICE DDL link into a custom PCI receiver card (HLT-RORC). These boards also provide a FPGA co-processor for data-intensive tasks of pattern recognition. Some of the pattern recognition algorithms (cluster finder, Hough transformation) have been re-designed in VHDL to be executed in the Virtex-4 FPGA on the HLT-RORC. HLT prototypes were operated during the beam tests of the TPC and TRD detectors. The input and output interfaces to DAQ and the data flow inside of HLT were successfully tested. A full-scale prototype of the dimuon-HLT achieved the expected data flow performance. This system was finally embedded in a GRID-like system of several distributed clusters demonstrating the scalability and fault-tolerance of the HLT.
Real Time Conference, 2005. 14th IEEE-NPSS; 07/2005
-
[show abstract]
[hide abstract]
ABSTRACT: The ALICE high level trigger has to process data online, in order to select interesting (sub)events, or to compress data efficiently by modeling techniques. Focusing on the main data source, the time projection chamber (TPC), we present two pattern recognition methods under investigation: a sequential approach (cluster finder and track follower) and an iterative approach (track candidate finder and cluster deconvoluter). We show, that the former is suited for pp and low multiplicity PbPb collisions, whereas the latter might be applicable for high multiplicity PbPb collisions of dN/dy>3000. Based on the developed tracking schemes we show that using modeling techniques, a compression factor of around 10 might be achievable.
IEEE Transactions on Nuclear Science 07/2004; · 1.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The ALICE High-Level Trigger processes data online, to either select interesting (sub-) events, or to compress data efficiently by modeling techniques. Focusing on the main data source, the Time Projection Chamber, the architecure of the system and the current state of the tracking and compression methods are outlined. Comment: 6 pages, 5 figures, to be published in NIM A
03/2004;
-
H. Tilsner,
T. Alt,
K. Aurbakken,
G. Grastveit,
H. Helstrup,
V. Lindenstruth,
C. Loizides,
J. Nystrand,
D. Roehrich,
B. Skaali,
T. Steinbeck,
K. Ullaland,
A. Vestbo,
T. Vik
[show abstract]
[hide abstract]
ABSTRACT: One of the main tracking detectors of the forthcoming ALICE Experiment at the LHC is a cylindrical Time Projection Chamber (TPC) with an expected data volume of about 75MByte per event. This data volume, in combination with the presumed maximum bandwidth of 1.2GByte/s to the mass storage system, would limit the maximum event rate to 20Hz. In order to achieve higher event rates, online data processing has to be applied. This implies either the detection and read-out of only those events which contain interesting physical signatures or an efficient compression of the data by modeling techniques. In order to cope with the anticipated data rate, massive parallel computing power is required. It will be provided in form of a clustered farm of SMP-nodes, based on off-the-shelf PCs, which are connected with a high bandwidth low overhead network. This High-Level Trigger (HLT) will be able to process a data rate of 25GByte/s online. The front-end electronics of the individual sub-detectors is connected to the HLT via an optical link and a custom PCI card which is mounted in the clustered PCs. The PCI card is equipped with an FPGA necessary for the implementation of the PCI-bus protocol. Therefore, this FPGA can also be used to assist the host processor with first-level processing. The first-level processing done on the FPGA includes conventional cluster-finding for low multiplicity events and local track finding based on the Hough Transformation of the raw data for high multiplicity events. PACS: 07.05.-t Computers in experimental physics – 07.05.Hd Data acquisition: hardware and software – 29.85.+c Computer data analysis
European Physical Journal C 01/2004; 33:s1041-s1043. · 3.63 Impact Factor
-
G Agakichiev,
H Appelshäuser,
R Baur,
J Bielcikova,
P Braun-Munzinger,
A Cherlin,
A Drees,
S I Esumi,
K Filimonov,
Z Fraenkel, [......],
H J Specht,
J Stachel, H Tilsner,
I Tserruya,
C Voigt,
S Voloshin,
C Weber,
J P Wessels,
J P Wurm,
V Yurevich
[show abstract]
[hide abstract]
ABSTRACT: Elliptic flow and two-particle azimuthal correlations of charged hadrons and high-p(T) pions (p(T)>1 GeV/c) have been measured close to midrapidity in 158A GeV/c Pb+Au collisions by the CERES experiment. Elliptic flow (v(2)) rises linearly with p(T) to a value of about 10% at 2 GeV/c. Beyond p(T) approximately 1.5 GeV/c, the slope decreases considerably, possibly indicating a saturation of v(2) at high p(T). Two-pion azimuthal anisotropies for p(T)>1.2 GeV/c exceed the elliptic flow values by about 60% in midcentral collisions. These nonflow contributions are attributed to nearside and back-to-back jetlike correlations, the latter exhibiting centrality dependent broadening.
Physical Review Letters 01/2004; 92(3):032301. · 7.37 Impact Factor
-
T Alt,
G Grastveit,
H Helstrup,
V Lindenstruth,
C Loizides,
D Röhrich,
B Skaali,
T Steinbeck,
R Stock, H Tilsner,
K Ullaland,
A Vestbø,
T Vik,
A Wiebalck
[show abstract]
[hide abstract]
ABSTRACT: The ALICE experiment at LHC will implement a high-level trigger system for online event selection and/or data compression. The largest computing challenge is posed by the TPC detector, which requires real-time pattern recognition. The system entails a very large processing farm that is designed for an anticipated input data stream of 25 GB s −1 . In this paper, we present the architecture of the system and the current state of the tracking methods and data compression applications.
J. Phys. G: Nucl. Part. Phys. 01/2004; 30:1097-1100.
-
D. Adamová,
G. Agakichiev,
H. Appelshäuser,
V. Belaga,
P. Braun-Munzinger,
R. Campagnolo,
A. Castillo,
A. Cherlin,
S. Damjanović,
T. Dietel, [......],
M. Šumbera, H. Tilsner,
I. Tserruya,
J.P. Wessels,
T. Wienold,
B. Windelband,
J.P. Wurm,
W. Xie,
S. Yurevich,
V. Yurevich
[show abstract]
[hide abstract]
ABSTRACT: Measurements of event-by-event fluctuations of the mean transverse momentum in PbAu collisions at 40, 80, and 158 are presented. A significant excess of mean pT fluctuations at mid-rapidity is observed over the expectation from statistically independent particle emission. The results are somewhat smaller than recent measurements at RHIC. A possible non-monotonic behavior of the mean pT fluctuations as function of collision energy, which may have indicated that the system has passed the critical point of the QCD phase diagram in the range of μB under investigation, has not been observed. The centrality dependence of mean pT fluctuations in PbAu is consistent with an extrapolation from pp collisions assuming that the non-statistical fluctuations scale with multiplicity. The results are compared to calculations by the rqmd and urqmd event generators.
Nuclear Physics A 10/2003; · 1.54 Impact Factor
-
G. Grastveit,
H. Helstrup,
V. Lindenstruth,
C. Loizides,
D. Roehrich,
B. Skaali,
T. Steinbeck,
R. Stock, H. Tilsner,
K. Ullaland,
A. Vestbo,
T. Vik
[show abstract]
[hide abstract]
ABSTRACT: The High Level Trigger (HLT) of the ALICE experiment requires massive parallel computing. One of the main tasks of the HLT system is two-dimensional cluster finding on raw data of the Time Projection Chamber (TPC), which is the main data source of ALICE. To reduce the number of computing nodes needed in the HLT farm, FPGAs, which are an intrinsic part of the system, will be utilized for this task. VHDL code implementing the Fast Cluster Finder algorithm, has been written, a testbed for functional verification of the code has been developed, and the code has been synthesized
07/2003;
-
D Adamová,
G Agakichiev,
H Appelshäuser,
V Belaga,
P Braun-Munzinger,
A Cherlin,
S Damjanović,
T Dietel,
L Dietrich,
A Drees, [......],
M Sumbera, H Tilsner,
I Tserruya,
J P Wessels,
T Wienold,
B Windelband,
J P Wurm,
W Xie,
S Yurevich,
V Yurevich
[show abstract]
[hide abstract]
ABSTRACT: We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2<m</=1 GeV/c(2) is enhanced over the expectation from neutral meson decays by a factor of 5.9+/-1.5(stat)+/-1.2(syst data)+/-1.8(syst meson decays), somewhat larger than previously observed at the higher energy of 158 AGeV. The results are discussed with reference to model calculations based on pi(+)pi(-)-->e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.
Physical Review Letters 07/2003; 91(4):042301. · 7.37 Impact Factor
-
Nuclear Physics A 02/2003; 715:607-610. · 1.54 Impact Factor
-
D Adamová,
G Agakichiev,
H Appelshäuser,
V Belaga,
P Braun-Munzinger,
A Castillo,
A Cherlin,
S Damjanović,
T Dietel,
L Dietrich, [......],
M Sumbera, H Tilsner,
I Tserruya,
J P Wessels,
T Wienold,
B Windelband,
J P Wurm,
W Xie,
S Yurevich,
V Yurevich
[show abstract]
[hide abstract]
ABSTRACT: Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda(f) reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider.
Physical Review Letters 02/2003; 90(2):022301. · 7.37 Impact Factor
