NA60 results on the ρ spectral function in In-In collisions

Damjanović, S.

doi:10.1016/j.nuclphysa.2006.11.015

Cited by 119 publications

(163 citation statements)

References 14 publications

(23 reference statements)

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“…[95]). Specifically, we evaluate the following scenarios, as sum-marized in the six panels of [15][16][17][18][19][20] MeV in the LMR, approximately reflecting the increase in the hadronic fireball temperatures (e.g., T fo = 136 MeV compared to T fo = 120 MeV at thermal freezeout). Scenario EoS-B (b) additionally improves around the ρ peak due to a larger weight of the relatively hard components from decays of freezeout and primordial ρ, since the overall thermal hadronic emission is smaller than for EoS-A and EoS-C (compare Fig.…”

Section: Slope Analysismentioning

confidence: 99%

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Dilepton radiation at the CERN super-proton synchrotron

2008

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A quantitative evaluation of dilepton sources in heavy-ion reactions is performed taking into account both thermal and non-thermal production mechanisms. The hadronic thermal emission rate is based on an electromagnetic current-correlation function with a low-mass region (LMR, M 1 GeV) dominated by vector mesons (ρ, ω, φ) and an intermediate-mass region (IMR, 1 GeV ≤ M ≤ 3 GeV) characterized by (the onset of) a multi-meson continuum. A convolution of the emission rates over a thermal fireball expansion results in good agreement with experiment in the low-mass spectra, confirming the predicted broadening of the ρ meson in hadronic matter in connection with the prevalence of baryon-induced medium effects. The absolute magnitude of the LMR excess is mostly controlled by the fireball lifetime, which in turn leads to a consistent explanation of the dilepton excess in the IMR in terms of thermal radiation. The analysis of experimental transversemomentum (qT ) spectra reveals discrepancies with thermal emission for qT 1 GeV in noncentral In-In collisions, which we address by extending our calculations by: (i) a refined treatment of ρ decays at thermal freezeout, (ii) primordially produced ρ's subject to energy-loss, (iii) Drell-Yan annihilation, and (iv) thermal radiation from t-channel meson exchange processes. We investigate the sensitivity of dilepton spectra to the critical temperature and hadro-chemical freezeout of the fireball. The ρ broadening in the LMR turns out to be robust, while in the IMR Quark-Gluon Plasma radiation is moderate unless the critical temperature is rather low.

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Section: Slope Analysismentioning

confidence: 99%

“…[16,17]). While the inclusive mass spectra are well described, the comparison of the calculations with newly released transverse pair-momentum (q T ) spectra [18] reveals some discrepancies at q T > 1 GeV in semicentral In-In.…”

Section: Introductionmentioning

confidence: 99%

Dilepton radiation at the CERN super-proton synchrotron

2008

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“…The acceptance shows strong variations with mass and p T [9,10], but is understood on the level of <10%, mainly based on a detailed study of the peripheral data for the particle ratios =! and =!…”

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confidence: 99%

Evidence for Radial Flow of Thermal Dileptons in High-Energy Nuclear Collisions

Arnaldi¹,

Banicz²,

Castor³

et al. 2008

Phys. Rev. Lett.

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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 T eff extracted from the spectra rises with dimuon mass up to the , 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.

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“…The latter are, in turn, obtained with acceptance corrections determined in an iterative way from MC simulations matched to the data in M and p T . The y-distribution is found to have the same rapidity width as dN ch /dη, σ y ∼ 1.5 [18]. The cosθ CS distributions for two mass windows of the excess and the ω are contained in [14].…”

Section: Introductionmentioning

confidence: 81%

“…The remainder of this paper is solely concerned with excess data fully corrected for acceptance and pair efficiencies [13,18]. In principle, the correction requires a 4-dimensional grid in the space of Mp T -y-cosθ CS (where θ CS is the polar angle of the muons in the Collins Soper frame).…”

Section: Introductionmentioning

confidence: 99%

Thermal dileptons in high-energy nuclear collisions

Damjanović

2009

Progress in Particle and Nuclear Physics

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Clear signs of excess dileptons above the known sources were found at the SPS since long. However, a real clarification of these observations was only recently achieved by NA60, measuring dimuons with unprecedented precision in 158A GeV In-In collisions. The excess mass spectrum in the region M <1 GeV is consistent with a dominant contribution fromThe associated ρ spectral function shows a strong broadening, but essentially no shift in mass. In the region M >1 GeV, the excess is found to be prompt, not due to enhanced charm production. The inverse slope parameter T eff associated with the transverse momentum spectra rises with mass up to the ρ, followed by a sudden decline above. While the initial rise, coupled to a hierarchy in hadron freeze-out, points to radial flow of a hadronic decay source, the decline above signals a transition to a low-flow source, presumably of partonic origin. The mass spectra show the steep rise towards low masses characteristic for Planck-like radiation. The polarization of the excess referred to the Collins Soper frame is found to be isotropic. All observations are consistent with a global interpretation of the excess as thermal radiation. We conclude with a short discussion of a possible link to direct photons.

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NA60 results on the ρ spectral function in In-In collisions

Cited by 119 publications

References 14 publications

Dilepton radiation at the CERN super-proton synchrotron

Dilepton radiation at the CERN super-proton synchrotron

Evidence for Radial Flow of Thermal Dileptons in High-Energy Nuclear Collisions

Thermal dileptons in high-energy nuclear collisions

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