-
Sérgio Ramos,
Collaboration,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beolè, [......],
F. Sigaudo,
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
T. Wu
[show abstract]
[hide abstract]
ABSTRACT: The NA50 experiment deals with Pb-Pb collisions at 158 GeV/nucleon at the CERN SPS accelerator. TheJ/ψ production is studied through the muon decay channel, using the Drell-Yan dimuons as a reference. New results based on recent
analyses, from data taken with improved experimental conditions and using different centrality estimators, are presented and
compared to an update of those already obtained from previous data samples. The stepwise pattern of the anomalousJ/ψ suppression as a function of centrality, already present in these previous results, is confirmed. This observation could
be a fingerprint of the theoretically predicted melting of charmonia resonances in a deconfined quark-gluon plasma.
Pramana 05/2012; 62(3):627-630. · 0.57 Impact Factor
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Paula bordalo,
M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beolé, [......],
F. Sigaudo,
S. Silva,
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis
[show abstract]
[hide abstract]
ABSTRACT: TheJ/Ψ production in 158 A GeV Pb-Pb interactions is studied, in the dimuon decay channel, as a function of centrality, as measured
with the electromagnetic or, alternatively, with the very forward hadronic calorimeters. After a first sharp variation at
mid-centrality, both patterns continue to fall down and exhibit a curvature change at high centrality values. This trend excludes
any conventional hadronic model and finds a natural explanation in a deconfined quark-gluon phase scenario.
Pramana 04/2012; 60(4):817-828. · 0.57 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The focusing property of thick chirped hologram PDLC gratings is investigated theoretically. Focal length's formula for linearly chirped gratings is obtained by using Bragg condition. Diffraction efficiency dependence on incident angle in focus point is calculated numerically and enhanced bandwidth is observed.
Transparent Optical Networks, 2007. ICTON '07. 9th International Conference on; 08/2007
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M. R. Atayan,
Bai Yuting,
E. A. De Wolf,
A. M. F. Endler,
Fu Jinghua,
H. Gulkanyan, R. Hakobyan,
Huang Yanping,
W. Kittel,
Liu Lianshou,
Li Zhiming,
Z. V. Metreveli,
L. N. Smirnova,
L. A. Tikhonova,
A. G. Tomaradze,
Wu Yuanfang,
S. A. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: Rapidity, azimuthal and multiplicity dependence of mean transverse momentum and transverse momentum correlations of charged particles is studied in π+p and K+p collisions at 250 GeV/c incident beam momentum. For the first time, it is found that the rapidity dependence of the two-particle transverse momentum correlation is different from that of the mean transverse momentum, but both have similar multiplicity dependence. In particular, the transverse momentum correlations are boost invariant. This is similar to the recently found boost invariance of the charge balance function. A strong azimuthal dependence of the transverse momentum correlations originates from the constraint of energy-momentum conservation. The results are compared with those from the PYTHIA Monte Carlo generator. The similarities to and differences with the results from current heavy ion experiments are discussed.
Phys. Rev. D. 04/2006; 73(7).
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F. Prino,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole,
V. Boldea, [......],
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
T. Wu,
N. A. collaboration
[show abstract]
[hide abstract]
ABSTRACT: Angular distributions of charged particles produced in Pb-Pb collisions at the CERN SPS have been measured by the NA50 experiment. Measurements have been performed with a silicon microstrip detector at two different beam energies (40 and 158 GeV/nucleon) and over a wide impact parameter (centrality) range. The centrality of the collision has been evaluated both by neutral transverse energy released in the interaction and by spectator nucleons energy (zero degree energy). The charged particle density at midrapidity shows a linear dependence on the number of participating nucleons at both beam energies. The particle density per participant pair and its root s dependence are also studied.
Focus on Multiplicity: International Workshop on Particle Multiplicity in Relativistic Heavy Ion Collisions. 01/2005; 5:86-96.
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M. R. Atayan,
Bai Yuting,
E A De Wolf,
A. M. F. Endler,
Fu Jinghua,
H. Gulkanyan, R. Hakobyan,
W. Kittel,
Liu Lianshou,
Li Zhiming,
Z V Metreveli,
L N Smirnova,
L A Tikhonova,
A G Tomaradze,
Wu Yuanfang,
S.A. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: We report on measurements of event-by-event charge fluctuations in $\pi^{+}\rp$ and $\rK^{+}\rp$ collisions at 250 GeV/$c$. The dependence of these fluctuations on the size of the rapidity windows are presented for the first time in the full phase space domain. The corrections for the influence of global charge conservation and leading-particle stopping are tested by the data. The discrepancy due to incomplete correction given by STAR and PHENIX are estimated. The dependence of the fluctuations on the position of the rapidity bin and on the multiplicity at different rapidity windows are also presented. Comment: 4pages, 3figures
11/2004;
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R. Arnaldi,
B. Alessandro,
C. Alexa,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole,
V. Boldea,
P. Bordalo, [......],
E. Scalas,
E. Scomparin,
S. Serci,
F. Sigaudo,
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
N. A. Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The NA50 experiment at CERN SPS has studied charmonium production in Pb-Pb collisions at 158 GeV/c per nucleon. According to the theoretical predictions the observation of the suppression of the J/psi production yield is expected to be an unambiguous probe for a phase transition from ordinary nuclear matter towards a state in which quarks and gluons are deconfined.
Acta Physica Hungarica New Series-Heavy Ion Physics. 01/2004; 19(3-4):337-341.
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Denis Jouan,
B Alessandro,
C Alexa,
R Arnaldi,
M Atayan,
C Baglin,
A Baldit,
M Bedjidian,
S Beolè,
V Boldea, [......],
F Sigaudo,
M Sitta,
P Sonderegger,
X Tarrago,
N S Topilskaya,
G L Usai,
E Vercellin,
L Villatte,
N Willis,
T Wu
[show abstract]
[hide abstract]
ABSTRACT: From proton, deuteron, S- and Pb-induced reactions, experiments NA38 and NA50 have measured muon pair production with various targets. In particular, the production rates of the , ω and ρ mesons have been simultaneously extracted and compared. Preliminary partial results of the most recent Pb–Pb measurement done in year 2000 by NA50 are presented here. They are also included in the comparison with the results obtained with lighter interacting nuclei.
Journal of Physics G Nuclear and Particle Physics 12/2003; 30(1):S277. · 4.18 Impact Factor
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Collaboration,
L. Ramello,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beolè, [......],
F. Sigaudo,
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
T. Wu
Nuclear Physics A 02/2003; 715:243-251. · 1.54 Impact Factor
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B. Alessandro,
C. Alexa,
R. Arnaldi,
J. Astruc,
M. Atayan,
C. Baglin,
A. Baldit,
S. Beole,
V. Boldea,
P. Bordalo, [......],
F. Sigaudo,
S. Silva,
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis
[show abstract]
[hide abstract]
ABSTRACT: The production of vector mesons phi, rho and omega has been measured in Pb-Pb collisions at 158 GeV/c per nucleon incident momentum at the CERN/SPS. The muon spectrometer of experiment NA50 detects phi, rho and omega mesons via their mu(+)mu(-) decay channel in the collision center of mass rapidity range 0 less than or equal to gamma(CM) less than or equal to 1. The results reported here show that the relative production of the phi compared to the (rho + omega) and the phi multiplicity per participant nucleon (N-part) increase with the centrality of the collision. On the other hand, the (p + w) multiplicity per participant does not exhibit any N-part dependence within our errors. The inverse slope parameter as deduced from an exponential fit to the phi transverse mass distribution is 228 +/- 10 MeV. Our results are compared with those obtained by experiment NA49 and with theoretical calculations. (C) 2003 Elsevier Science B.V. All rights reserved.
Physics Letters B. 01/2003; 555(3-4):147-154.
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M R Atayan,
Bai Yuting,
E A De Wolf,
A M F Endler,
Fu Jinghua,
H Gulkanyan, R Hakobyan,
W Kittel,
Liu Lianshou,
Z V Metreveli,
L N Smirnova,
L A Tikhonova,
A G Tomaradze,
F Verbeure,
Wu Yuanfang,
S A Zotkin
[show abstract]
[hide abstract]
ABSTRACT: We report results on event-by-event fluctuations of transverse momentum, Phi(p(t)), in pi(+)p and K(+)p collisions at 250 GeV/c. For the first time, their dependence on rapidity region, transverse momentum acceptance, multiplicity, mean transverse momentum per event, and on the correlation between transverse momentum and multiplicity are systematically presented. The results are compared with those from the PYTHIA Monte Carlo generator. The fluctuations under the same acceptance cuts as used in current heavy-ion experiments are also presented.
Physical Review Letters 10/2002; 89(12):121802. · 7.37 Impact Factor
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C Quintans,
M C Abreu,
B Alessandro,
C Alexa,
R Arnaldi,
M Atayan,
C Baglin,
A Baldit,
M Bedjidian,
S Beolè, [......],
F Sigaudo,
S Silva,
M Sitta,
P Sonderegger,
X Tarrago,
N S Topilskaya,
G L Usai,
E Vercellin,
L Villatte,
N Willis
[show abstract]
[hide abstract]
ABSTRACT: The experiment NA50 studies the strangeness production by means of the BRμμσ/(BRρμμσρ + BRωμμσω) cross-sections ratio in relativistic heavy ion collisions with respect to proton and light ion collisions. New results for Pb+Pb interactions at 158 A GeV/c are presented (1998 data) and analysed with a different method. The BRμμσ/(BRρμμσρ + BRωμμσω) ratio shows an increase with the number of participants, in agreement with previous results. The inverse slope parameter extracted from the MT universal scaling is also studied.
Journal of Physics G Nuclear and Particle Physics 06/2002; 28(7):1809. · 4.18 Impact Factor
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P. Bordalo,
M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole, [......],
S. Silva,
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
N. A. Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The J/psi production in Pb-Pb interactions induced by 158 GeV/c incident Pb ions is studied as a function of centrality, as estimated from the neutral transverse energy or, alternatively, from the very forward hadronic energy of the collision. The J/psi yield exhibits a similar pattern with a first drop for mid-peripheral collisions and a steady decrease for the most central reactions. Conventional hadronic models are unable, to fairly reproduce this trend which finds a natural explanation in a deconfined quark-gluon phase scenario. The J/psi transverse momentum distributions and their dependence with centrality are also reviewed in this presentation.
Nuclear Physics A. 01/2002; 698:127C-134C.
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M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
F. Bellaiche,
S. Beole, [......],
M. Sitta,
C. Soave,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
N. A. Collaboration
[show abstract]
[hide abstract]
ABSTRACT: Muon pairs produced in Pb-Pb interactions at 158 GeV/c per nucleon are used to study the transverse momentum distributions of the J/psi, psi' and dimuons in the mass continuum. In particular, the dependence of these distributions on the centrality of the Pb-Pb collision is investigated in detail. (C) 2001 Published by Elsevier Science B.V.
Physics Letters B. 01/2001; 499(1-2):85-96.
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P. Saturnini,
M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole, [......],
M. Sitta,
C. Soave,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
N. A. Collaborat
[show abstract]
[hide abstract]
ABSTRACT: In the search for the quark-gluon plasma at CERN SPS, several signals were observed suggesting that this new state of matter was actually produced in the interactions induced by the lead beam at 158A GeV. The transverse flow phenomena characterize the distribution of the particles in the final state of the collision, and are expected to provide some indications about the initial state. More precisely the existence of an elliptic flow directed along the reaction plane in the case of the non central collisions of two spherical nuclei, has been proposed to probe the thermalisation of the initial state. Indeed. the NA50 collaboration has measured these kind of effects in Pb-Pb collisions at 158A GeV, and we can conclude that the thermalisation of the initial state is actually present in these interactions. Conversely. there is no evidence for such a thermalisation in the NA38 data which were obtained with the sulphur beam at 200A GeV, neither in S-S nor in S-Cu interactions.
Nuclear Physics B-Proceedings Supplements. 01/2001; 92:55-61.
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D. Jouan,
M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole, [......],
M. Sitta,
C. Soave,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
N. A. experiment
[show abstract]
[hide abstract]
ABSTRACT: We present a set of results obtained by experiment NA50 at the CERN SPS. In Pb-Pb collisions, the phi meson yield and the muon pair mass continuum in the invariant mass range (1.5 - 2.5 GeV/c(2)) exhibit a significant enhancement which increases with the centrality of the collision. The measured J/psi suppression pattern rules out conventional hadronic scenarios and provides evidence for quark-gluon deconfinement.
Nuclear Physics A. 01/2001; 681:157C-164C.
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M. Monteno,
M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole, [......],
M. Sitta,
C. Soave,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
N. A. Collaborat
[show abstract]
[hide abstract]
ABSTRACT: The NA50 experiment has measured, at the CERN SPS: the dimuon production in Pb-Pb collisions at 158 GeV/c per nucleon, following the program of the previous NA38 and NA51 experiments, performed with proton and light ion beams. The J/psi production has been studied by NA50 as a function of the centrality of the collisions. The results of the analyses performed on three data samples, collected from 1995 to 1998 show that for peripheral collisions the J/Psi cross section can be understood in terms of ordinary nuclear absorption: consistently with the extrapolation of previous measurements extending from p-p to S-U. On the contrary, the central events show an anomalous J/Psi suppression, and the pattern of J/Psi yield versus centrality features two discontinuities that cannot be described by conventional models based on hadronic scenarios. These results can be considered as a strong indication of the creation of a new state of matter in central Pb-Pb collisions at the SPS.
Nuclear Physics B-Proceedings Supplements. 01/2001; 92:43-54.
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M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole,
V. Boldea, [......],
S. Silva,
M. Sitta,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
N. A. Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The observation of an anomalous J/psi suppression in Pb-Pb collisions by the NA50 Collaboration can be considered as the most striking indication for the deconfinement of quarks and gluons at SPS energies. In this Letter, we determine the J/psi suppression pattern as a function of the forward hadronic energy E-ZDC measured in a Zero Degree Calorimeter (ZDC). The direct connection between EZDC and the geometry of the collision allows us to calculate, within a Glauber approach, the precise relation between the number of participant nucleons N-part and E-ZDC. Then, we check if the experimental data can be better explained by a sudden or a smooth onset of the anomalous J/psi suppression as a function of the number of participants. (C) 2001 Elsevier Science B.V. All rights reserved.
Physics Letters B. 01/2001; 521(3-4):195-203.
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M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
M. Atayan,
C. Baglin,
A. Baldit,
M. Bedjidian,
S. Beole,
V. Boldea, [......],
M. Sitta,
C. Soave,
P. Sonderegger,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
E. Vercellin,
L. Villatte,
N. Willis,
N. A. Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The J/psi production in 158 A GeV Pb-Pb interactions is studied as a function of centrality. Its pattern, after a first sharp variation around E-T= 40 GeV, continues to fall down and exhibits a curvature change around E-T= 90 GeV. This trend excludes any conventional hadronic model and is in agreement with a deconfined quark-gluon phase scenario.
Intersections of Particle and Nuclear Physics. 01/2000; 549:341-345.
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M. C. Abreu,
B. Alessandro,
C. Alexa,
R. Arnaldi,
J. Astruc,
M. Atayan,
C. Baglin,
A. Baldisseri,
A. Baldit,
M. Bedjidian, [......],
M. Sitta,
C. Soave,
P. Sonderegger,
F. Staley,
X. Tarrago,
N. S. Topilskaya,
G. L. Usai,
J. Varela,
E. Vercellin,
N. Willis
[show abstract]
[hide abstract]
ABSTRACT: The low mass dimuon spectra collected in p-U collisions by the NA38 experiment significantly exceeds the total cross section expected from previous analysis, done by other experiments. The 'excess' events have a harder p(T) distribution than the muon pairs from eta and omega Dalitz decays, expected to dominate the mass window 0.4-0.65 GeV/c(2). We conjecture that the excess events may be due to q (q) over bar annihilations, negligible at low p(T) but made visible by the m(T) cut applied in the NA38 data. Taking this assumption to parametrise the p-U spectra, we proceed with the corresponding analysis of the S-Cu, S-U and Pb-Pb data, collected by the NA38 and NA50 experiments, comparing the measured low mass dimuon spectra with the 'expected cocktail'.
European Physical Journal C. 01/2000; 13(1):69-78.
