This report reviews the study of open heavy-flavour and quarkonium production in high-energy hadronic collisions, as tools to investigate fundamental aspects of Quantum Chromodynamics, from the ...proton and nucleus structure at high energy to deconfinement and the properties of the Quark–Gluon Plasma. Emphasis is given to the lessons learnt from LHC Run 1 results, which are reviewed in a global picture with the results from SPS and RHIC at lower energies, as well as to the questions to be addressed in the future. The report covers heavy flavour and quarkonium production in proton–proton, proton–nucleus and nucleus–nucleus collisions. This includes discussion of the effects of hot and cold strongly interacting matter, quarkonium photoproduction in nucleus–nucleus collisions and perspectives on the study of heavy flavour and quarkonium with upgrades of existing experiments and new experiments. The report results from the activity of the SaporeGravis network of the I3 Hadron Physics programme of the European Union 7
th
Framework Programme.
We report on a precision measurement of low-mass muon pairs in 158 AGeV indium-indium collisions at the CERN SPS. A significant excess of pairs is observed above the yield expected from neutral meson ...decays. The unprecedented sample size of 360,000 dimuons and the good mass resolution of about 2% allow us to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum is consistent with a dominant contribution from pi+pi- -->rho -->mu+mu- annihilation. The associated space-time averaged spectral function shows a strong broadening, but essentially no shift in mass. This may rule out theoretical models linking hadron masses directly to the chiral condensate.
The NA60 experiment has studied low-mass muon pair production in proton–nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The ...transverse momentum spectra of the
ρ
/
ω
and
ϕ
mesons are measured in the full
p
T
range accessible, from
p
T
=
0
up to
2
GeV/c
. The nuclear dependence of the production cross sections of the
η
,
ω
and
ϕ
mesons has been found to be consistent with the power law
σ
pA
∝
A
α
, with the
α
parameter increasing as a function of
p
T
for all the particles, and an approximate hierarchy
α
η
≈
α
ϕ
>
α
ω
. The cross section ratios
σ
η
/
σ
ω
,
σ
ρ
/
σ
ω
and
σ
ϕ
/
σ
ω
have been studied as a function of the size A of the production target, and an increase of the
η
and
ϕ
yields relative to the
ω
is observed from p–Be to p–U collisions.
We report a new determination of the strange quark contribution to the proton's magnetic form factor at a four-momentum transfer Q2=0.1 (GeV/c)2 from parity-violating e–p elastic scattering. The ...result uses a revised analysis of data from the SAMPLE experiment which was carried out at the MIT-Bates Laboratory. The data are combined with a calculation of the proton's axial form factor GeA to determine the strange form factor GsM(Q2=0.1)=0.37±0.20±0.26±0.07. The extrapolation of GsM to its Q2=0 limit and comparison with calculations is also discussed.
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.
NA60 results on thermal dimuons Arnaldi, R.; Banicz, K.; Borer, K. ...
European physical journal. C, Particles and fields,
06/2009, Letnik:
61, Številka:
4
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158
A
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
π
+
π
−
→
ρ
→
μ
+
μ
−
annihilation. The associated
ρ
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
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
<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
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.
The NA60 experiment has studied J/ψ production in p–A collisions at 158 and 400 GeV, at the CERN SPS. Nuclear effects on the J/ψ yield have been estimated from the A-dependence of the production ...cross section ratios σJ/ψA/σJ/ψBe (A=Al, Cu, In, W, Pb, U). We observe a significant nuclear suppression of the J/ψ 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 x2, the fraction of the nucleon momentum carried by the interacting parton in the target nucleus.
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.
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
π
+
π
−
→
ρ
→
μ
+
μ
−
annihilation. The associated
ρ spectral function exhibits considerable broadening, but essentially no shift in mass. The acceptance-corrected
p
T
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
p
T
spectra are compared to recent theoretical predictions.
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