In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose–Einstein correlations of identical bosons at low relative momentum. The source ...radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correlations in pp, p–Pb and Pb–Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p–Pb collisions are found to be 5–15% larger than those in pp, while those in Pb–Pb are 35–55% larger than those in p–Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p–Pb as compared to pp collisions at similar multiplicity.
Results of a two-particle correlation analysis of high-pt charged particles in Pb–Au collisions at 158A GeV/c are presented. The data have been recorded by the CERES experiment at the CERN-SPS. The ...correlations are studied as function of transverse momentum, particle charge and collision centrality. We observe a jet-like structure in the vicinity of a high-pt trigger particle and a broad back-to-back distribution. The yields of associated particles per trigger show a strong dependence on the trigger/associate charge combination. A comparison to PYTHIA confirms the jet-like pattern at the near-side but suggests a strong modification at the away-side, implying significant energy transfer of the hard-scattered parton to the medium.
The CERES/NA45 experiment at the CERN-SPS is dedicated to study the production of e
+e
−-pairs in ultrarelativistic heavy ion collisions. Compared to extrapolations from results obtained in ...proton-induced reactions, it has previously observed an enhanced production in S-Au 1 and Pb-Au 2 collisions. To verify this enhancement and to study its properties, higher statistics were accumulated during a runtime in 1996. We report here, for the first time, on the results of this analysis (for details see ref. 3).
Hadronic spectra from interactions of Pb on Au at 158 AGeV/c have been measured by the CERES experiment at the CERN SPS. We report on preliminary results on transverse mass spectra of identified ...pions and negative hadrons as well as spectra of the positive charge excess obtained by subtracting the negative particle distribution from that of positive tracks. We have also performed a study of the event azimuthal anisotropies which give evidence for directed and elliptic flow in non-central collisions.
Event-by-event fluctuations at SPS Appelshäuser, Harald; Sako, Hiro; Adamová, D. ...
Nuclear physics. A,
04/2005, Letnik:
752
Journal Article
Recenzirano
Odprti dostop
Results on event-by-event fluctuations of the mean transverse momentum and net charge in Pb-Au collisions, measured by the CERES Collaboration at CERN-SPS, are presented. We discuss the centrality ...and beam energy dependence and compare our data to cascade calculations.
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.
The CERES/NA45 experiment at the CERN SPS was upgraded in 1998 by the addition of a cylindrical Time Projection Chamber. The aim is to improve the mass resolution of e
+e
− pairs in the ρ/ω/φ region ...to Δ
m/
m < 2%. A progress report is given on the TPC performance during the 1998 commissioning runs (laser rays, beam halo muons, and particles produced by proton/π and lead beams hitting Pb and Au targets).
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