-
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;
-
The Collaboration,
R. Arnaldi,
K. Banicz,
K. Borer,
J. Castor,
B. Chaurand,
W. Chen,
C. Cicalò,
A. Colla,
P. Cortese, [......],
J. Seixas,
S. Serci,
R. Shahoyan,
P. Sonderegger,
H. J. Specht,
R. Tieulent,
A. Uras,
G. Usai,
R. Veenhof,
H. K. Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment has measured muon pair production in In–In collisions at 158 AGeV at the CERN SPS. This paper presents
a high statistics measurement of φ→μ
μ meson production. Differential spectra, yields, mass and width are measured as a function of centrality and compared to previous
measurements in other colliding systems at the same energy. The width of the rapidity distribution is found to be constant
as a function of centrality, compatible with previous results. The decay muon polar angle distribution is measured in several
reference frames. No evidence of polarization is found as a function of transverse momentum and centrality. The analysis of
the p
T
spectra shows that the φ has a small radial flow, implying a weak coupling to the medium. The T
eff parameter measured in In–In collisions suggests that the high value observed in Pb–Pb in the kaon channel is difficult to
reconcile with radial flow alone. The absolute yield is compared to results in Pb–Pb collisions: though significantly smaller
than measured by NA50 in the muon channel, it is found to exceed the NA49 and CERES data in the kaon channel at any centrality.
The mass and width are found to be compatible with the PDG values at any centrality and at any p
T
: no evidence for in-medium modifications is observed.
European Physical Journal C 04/2012; 64(1):1-18. · 3.63 Impact Factor
-
Collaboration,
R. Arnaldi,
K. Banicz,
K. Borer,
J. Castor,
B. Chaurand,
W. Chen,
C. Cicalò,
A. Colla,
P. Cortese, [......],
E. Scomparin,
J. Seixas,
S. Serci,
R. Shahoyan,
P. Sonderegger,
H. J. Specht,
R. Tieulent,
G. Usai,
R. Veenhof,
H. K. Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158 AGeV In–In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2<M<2.6GeV. The mass spectrum for M<1GeV is consistent with a dominant contribution from π
+
π
−→ρ→μ
+
μ
− annihilation. The associated ρ spectral function shows a strong broadening, but essentially no shift in mass. For M>1GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell–Yan pairs.
The slope parameter T
eff associated with the transverse momentum spectra rises with mass up to the ρ, followed by a sudden decline above. The rise for M<1GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M>1GeV and its relation to parton–hadron duality is discussed in detail, suggesting a dominantly partonic emission source
in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated
empirical evidence, including also a Planck-like shape of the mass spectra at low p
T
and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude
with first results on ω in-medium effects.
European Physical Journal C 04/2012; 61(4):711-720. · 3.63 Impact Factor
-
Collaboration,
R. Arnaldi,
K Banicz,
J. Castor,
B Chaurand,
W Chen,
C Cicalò,
A. Colla,
P. Cortese, S. Damjanovic, [......],
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
A. Uras,
G. Usai,
R Veenhof,
H K Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has studied $\phi$ meson production in
In-In collisions at 158A GeV via both the $K^+K^-$ and the $\mu^+\mu^-$ decay
channels. The yields and inverse slope parameters of the $m_T$ spectra observed
in the two channels are compatible within errors, different from the large
discrepancies seen in Pb-Pb collisions between the hadronic (NA49) and dimuon
(NA50) decay channels. Possible physics implications are discussed.
04/2011;
-
R. Arnaldi,
K Banicz,
J. Castor,
B Chaurand,
W Chen,
C. Cicalo,
A. Colla,
P. Cortese, S. Damjanovic,
A David, [......],
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
A. Uras,
G. Usai,
R Veenhof,
H. K. Woehri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment has studied J/psi production in p-A collisions at 158 and
400 GeV, at the CERN SPS. Nuclear effects on the J/psi yield have been
estimated from the A-dependence of the production cross section ratios
sigma_{J/psi}^{A}/sigma_{J/psi}^{Be} (A=Al, Cu, In, W, Pb, U). We observe a
significant nuclear suppression of the J/psi yield per nucleon-nucleon
collision, with a larger effect at lower incident energy, and we compare this
result with previous observations by other fixed-target experiments. An attempt
to disentangle the different contributions to the observed suppression has been
carried out by studying the dependence of nuclear effects on x_2, the fraction
of nucleon momentum carried by the interacting parton in the target nucleus.
04/2010;
-
R. Arnaldi,
K. Banicz,
K. Borer,
J. Castor,
B. Chaurand,
W. Chen,
C. Cicalò,
A. Colla,
P. Cortese, S. Damjanovic, [......],
J. Seixas,
S. Serci,
R. Shahoyan,
P. Sonderegger,
H. J. Specht,
R. Tieulent,
A. Uras,
G. Usai,
R. Veenhof,
H. K. Wöhri
Nuclear Physics A 10/2009; 830:960-960. · 1.54 Impact Factor
-
A De Falco,
R. Arnaldi,
K Banicz,
K Borer,
J. Castor,
B Chaurand,
W Chen,
C. Cicalo,
A. Colla,
P. Cortese, [......],
E. Scomparin,
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
G. Usai,
R Veenhof,
H. Wöhri
[show abstract]
[hide abstract]
ABSTRACT: NA60 measured dimuon production in p-A and In-In collisions at the CERN SPS. This paper presents a high statistics measurement of $\phi$ meson production in In-In collisions at 158 AGeV. Both the transverse momentum, rapidity, decay angular distributions and the absolute yield were measured as a function of centrality. The results are compared to previous measurements in order to shed light on the long standing $\phi$ puzzle. In addition, highlights on $\eta$ meson production and on the dimuon excess below the J/$\psi$ mass are presented. Comment: 8 pages, 6 figures, proceedings of the Strangeness in Quark Matter 2008 conference (SQM08), Beijing, Oct.6-10, 2008
04/2009;
-
R Arnaldi,
K Banicz,
J Castor,
B Chaurand,
C Cicaì,
A Colla,
P Cortese, S Damjanovic,
A David,
A De Falco, [......],
E Scomparin,
J Seixas,
S Serci,
R Shahoyan,
P Sonderegger,
H J Specht,
R Tieulent,
G Usai,
R Veenhof,
H K Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158A GeV In-In collisions. The mass and p T spectra associated with peripheral collisions can quantitatively be described by the known neutral meson decays. The high data quality has allowed to remeasure the electromagnetic transition form factors of the Dalitz decays η→µ + µ − γ and ω→µ + µ − π 0 . Using the usual pole approximation F = (1 − M 2 /Λ 2) −1 for the form factors, we find Λ −2 (in GeV −2) to be 1.95±0.17(stat.)±0.05(syst.) for the η and 2.24±0.06(stat.)±0.02(syst.) for the ω. While the values agree with previous results from the Lepton-G experiment, the errors are greatly improved, confirming now on the level of 10σ the strong enhancement of the ω form factor beyond the expectation from vector meson dominance. An improved value of the branching ratio BR(ω → µ + µ − π 0) = [1.73±0.25(stat.)±0.14(syst.)]·10 −4 has been obtained as a byproduct.
03/2009; 8520.
-
R. Arnaldi,
K. Banicz,
K. Borer,
J. Castor,
B. Chaurand,
W. Chen,
C. Cicalò,
A. Colla,
P. Cortese, S. Damjanovic, [......],
E. Scomparin,
J. Seixas,
S. Serci,
R. Shahoyan,
P. Sonderegger,
H. J. Specht,
R. Tieulent,
G. Usai,
R. Veenhof,
H. K. Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The yield of muon pairs in the invariant mass region 1<M<2.5GeV/c
2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon
pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions.
In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson
production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of
this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to
the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons
are well described by an exponential function, with inverse slope values around 190MeV. The values are independent of mass
and significantly lower than those found at masses below 1GeV/c
2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1GeV/c
2 to be of largely partonic origin, when radial flow has not yet built up.
European Physical Journal C 01/2009; 59(3):607-623. · 3.63 Impact Factor
-
NA60 Collaboration,
R. Arnaldi,
K Banicz,
K Borer,
J. Castor,
B Chaurand,
W Chen,
C. Cicalo,
A. Colla,
P. Cortese, [......],
E. Scomparin,
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
G. Usai,
R Veenhof,
H. K. Woehri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2<M<2.6 GeV has previously been interpreted as thermal radiation. We now present first results on the associated angular distributions. Using the Collins-Soper reference frame, the structure function parameters \lambda, \mu and \nu are measured to be zero, and the projected distributions in polar and azimuth angles are found to be uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system. Comment: Submitted to Physical Review Letters
Physical Review Letters 12/2008; · 7.37 Impact Factor
-
NA60 Collaboration,
R. Arnaldi,
K Banicz,
K Borer,
J. Castor,
B Chaurand,
W Chen,
C. Cicalo,
A. Colla,
P. Cortese, [......],
E. Scomparin,
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
G. Usai,
R Veenhof,
H. K. Woehri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158A GeV In-In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2<M<2.6 GeV. The mass spectrum for M<1 GeV is consistent with a dominant contribution from pi+pi- -> rho -> mu+mu- annihilation. The associated rho spectral function shows a strong broadening, but essentially no shift in mass. For M>1 GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell-Yan pairs. The slope parameter Teff associated with the transverse momentum spectra rises with mass up to the rho, followed by a sudden decline above. The rise for M<1 GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M>1 GeV and its relation to parton-hadron duality is discussed in detail, suggesting a dominantly partonic emission source in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated empirical evidence, including also a Planck-like shape of the mass spectra at low pT and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude with first results on omega in-medium effects. Comment: 10 pages, 12 figures, submitted to Eur. Phys. J. C
12/2008;
-
NA60 Collaboration: R. Arnaldi,
K Banicz,
K Borer,
J. Castor,
B Chaurand,
W Chen,
C. Cicalo,
A. Colla,
P. Cortese, S. Damjanovic, [......],
E. Scomparin,
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
G. Usai,
R Veenhof,
H. K. Wohri
[show abstract]
[hide abstract]
ABSTRACT: The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c^2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c^2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c^2 to be of largely partonic origin, when radial flow has not yet built up.
11/2008;
-
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;
-
R Arnaldi,
K Banicz,
J Castor,
B Chaurand,
C Cicalò,
A Colla,
P Cortese, S Damjanovic,
A David,
A de Falco, [......],
E Scomparin,
J Seixas,
S Serci,
R Shahoyan,
P Sonderegger,
H J Specht,
R Tieulent,
G Usai,
R Veenhof,
H K Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff extracted from the spectra rises with dimuon mass up to the rho, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.
Physical Review Letters 02/2008; 100(2):022302. · 7.37 Impact Factor
-
R Arnaldi,
K Banicz,
J Castor,
B Chaurand,
C Cicalò,
A Colla,
P Cortese, S Damjanovic,
A David,
A de Falco, [......],
E Scomparin,
J Seixas,
S Serci,
R Shahoyan,
P Sonderegger,
H J Specht,
R Tieulent,
G Usai,
R Veenhof,
H K Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment studies muon pair production at the CERN Super Proton Synchrotron. In this Letter we report on a precision measurement of J/psi in In-In collisions. We have studied the J/psi centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than approximately 80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results.
Physical Review Letters 10/2007; 99(13):132302. · 7.37 Impact Factor
-
J Seixas,
R Arnaldi,
R Averbeck,
K Banicz,
J Castor,
B Chaurand,
C Cicalò,
A Colla,
P Cortese, S Damjanovic, [......],
P Rosinsky,
E Scomparin,
S Serci,
R Shahoyan,
P Sonderegger,
H J Specht,
R Tieulent,
G Usai,
R Veenhof,
H K Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 AGeV In–In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of close to 400K events and the good mass resolution of about 2% have made it possible to isolate the excess by subtraction of the decay sources (keeping the ρ). The shape of the resulting mass spectrum exhibits considerable broadening, but essentially no shift in mass. The acceptance-corrected transverse-momentum spectra have a shape atypical for radial flow and show a significant mass dependence, pointing to different sources in different mass regions.
Journal of Physics G Nuclear and Particle Physics 07/2007; 34(8):S1023. · 4.18 Impact Factor
-
A Ferretti,
R. Arnaldi,
R Averbeck,
K Banicz,
J. Castor,
B Chaurand,
C Cicalò,
A. Colla,
P. Cortese, S. Damjanovic, [......],
E. Scomparin,
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
G. Usai,
R Veenhof,
H. Wöhri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment is a fixed-target experiment at the CERN SPS. It has measured the dimuon yield in Indium--Indium collisions with an In beam of 158 AGeV/c and in p-A collisions with a proton beam of 400 and 158 AGeV/c. The results allow to address three important physics topics, namely the study of the rho spectral function in nuclear collisions, the clarification of the origin of the dimuon excess measured by NA50 in the intermediate mass range, and the J/psi suppression pattern in a collision system different from Pb-Pb. An overview of these results will be given in this paper.
06/2007;
-
R. Arnaldi,
NA60 Collaboration: R. Arnaldi,
R Averbeck,
K Banicz,
J. Castor,
B Chaurand,
C. Cicalo,
A. Colla,
P. Cortese, S. Damjanovic, [......],
E. Scomparin,
J Seixas,
S. Serci,
R. Shahoyan,
P Sonderegger,
H J Specht,
R. Tieulent,
G. Usai,
R Veenhof,
H. K. Wohri
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment has studied J/$\psi$ production in Indium-Indium collisions at 158 A$\cdot$GeV. In this paper we present an updated set of results obtained with the complete set of available statistics and an improved alignment of the vertex tracker. The centrality dependence of the J/$\psi$ production, obtained with an analysis technique based only on the J/$\psi$ sample, indicates that a suppression beyond that induced by nuclear absorption is present in In-In collisions, setting in at $\sim$80 participant nucleons. A first study of the systematic errors related with this measurement is discussed. We also present preliminary results on the J/$\psi$ azimuthal distributions.
02/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 AGeV In-In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. After subtraction of the decay sources, the shape of the resulting mass spectrum is largely consistent with a dominant contribution from pi+pi- -> rho -> mu+mu- annihilation. The associated rho spectral function exhibits considerable broadening, but essentially no shift in mass. The acceptance-corrected pT spectra have a shape atypical for radial flow. They also significantly depend on mass, pointing to different sources in different mass regions. Both mass and pT spectra are compared to recent theoretical predictions.
02/2007;
-
R. Arnaldi,
R. Averbeck,
K. Banicz,
J. Castor,
B. Chaurand,
C. Cicalo,
A. Colla,
P. Cortese, S. Damjanovic,
A. David, [......],
J. Seixas,
S. Serci,
R. Shahoyan,
P. Sonderegger,
H.J. Specht,
R. Tieulent,
G. Usai,
R. Veenhof,
H.K. Wöhri,
The Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158A GeV In–In collisions. A strong excess of pairs
is observed above the yield expected from neutral meson decays. The unprecedented sample size close to 400000 events and the
good mass resolution of about 2% made it possible to isolate the excess by subtraction of the decay sources. The shape of
the resulting mass spectrum shows some non-trivial centrality dependence, but is largely consistent with a dominant contribution
from π+π-→ϱ→μ+μ- annihilation. The associated ϱ spectral function exhibits considerable broadening, but essentially no shift in mass. The
pT-differential mass spectra show the excess to be much stronger at low pT than at high pT. The results are compared to theoretical model predictions; they tend to rule out models linking hadron masses directly to
the chiral condensate.
European Physical Journal C 12/2006; 49(1):235-241. · 3.63 Impact Factor
