NA60 results on<i>p<sub>T</sub></i>spectra and the ρ spectral function in In–In collisions

Seixas, J.; Arnaldi, R.; Averbeck, R.; Banicz, K.; Castor, J.; Chaurand, B.; Cicalò, C.; Colla, A.; Cortese, P.; Damjanović, S.; David, A.; Falco, A. De; Devaux, A.; Drees, A.; Ducroux, L.; En’yo, H.; Ferretti, A.; Floris, M.; Förster, A.; Force, P.; Guettet, N.; Guichard, A.; Gulkanian, H.; Keil, M.; Kluberg, L.; Lourenço, C.; Lozano, J.; Manso, F.; Masoni, A.; Martins, P.; Neves, A.; Ohnìshì, H.; Oppedisano, C.; Parracho, P. G. Ferreira; Pillot, P.; Puddu, G.; Radermacher, E.; Ramalhete, P.; Rosinský, P.; Scomparin, E.; Serci, S.; Shahoyan, R.; Sonderegger, P.; Specht, H.J.; Tieulent, R.; Usai, G. L.; Veenhof, R.; Wöhri, H. K.

doi:10.1088/0954-3899/34/8/s148

Cited by 20 publications

(10 citation statements)

References 13 publications

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“…However, for a robust conclusion one needs to subtract the D-meson background as e.g. in the NA60 data [74]. This gives a strong motivation for the STAR detector upgrade with a muon telescope [75].…”

Section: B Electromagnetic Observablesmentioning

confidence: 99%

Examinations of the early degrees of freedom in ultrarelativistic nucleus-nucleus collisions

et al. 2016

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The Parton-Hadron-String-Dynamics (PHSD) transport model is used to study the impact on the choice of initial degrees of freedom on the final hadronic and electromagnetic observables in Au+Au collisions at √ sNN = 200 GeV. We find that a non-perturbative system of massive gluons (scenario I) and a system dominated by quarks and antiquarks (scenario II) lead to different hadronic observables when imposing the same initial energy-momentum tensor Tµν (x) just after the passage of the impinging nuclei. In case of the gluonic initial condition the formation of s,s pairs in the QGP proceeds rather slow such that the anti-strange quarks and accordingly the K + mesons do not achieve chemical equilibrium even in central Au+Au collisions at √ sNN = 200 GeV. Accordingly, the K + rapidity distribution is suppressed in the gluonic scenario and in conflict with the data from the BRAHMS Collaboration. The proton and antiproton rapidity distributions also disfavor the scenario I. Furthermore, a clear suppression of direct photon and dilepton production is found for the pure gluonic initial conditions which is not so clearly seen in the present photon and dilepton spectra from Au+Au collisions at √ sNN = 200 GeV due to a large contribution from other channels. It is argued that dilepton spectra in the invariant mass range 1.2 GeV < M < 3 GeV will provide a definitive answer once the background from correlated D-meson decays is subtracted experimentally.

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Section: B Electromagnetic Observablesmentioning

confidence: 99%

Examinations of the early degrees of freedom in ultrarelativistic nucleus-nucleus collisions

et al. 2016

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“…For this it is necessary to separate the background from known dilepton sources -Dalitz decays of baryonic and mesonic resonances as well as pN and πN bremsstrahlung. At SPS energies of 40 and 158 AGeV such an enhancement above the known background has been measured by the CERES [15] and the NA60 [16] collaborations. The experimental results are compatible with the assumption that in the medium the peak position of the ρ meson mass distribution remains rather unchanged while the width increases considerably (cf.…”

Section: Introductionmentioning

confidence: 99%

System size and energy dependence of dilepton production in heavy-ion collisions at 1-2 GeV/nucleon energies

et al. 2013

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We study the dilepton production in heavy-ion collisions at energies of 1-2 AGeV as well as in proton induced pp, pn, pd and p + A reactions from 1 GeV up to 3.5 GeV where data have been taken by the HADES collaboration. For the analysis we employ three different transport modelsthe microscopic off-shell Hadron-String-Dynamics (HSD) transport approach, the Isospin Quantum Molecular Dynamics (IQMD) approach as well as the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) approach. We find that the HSD and IQMD models describe very reasonably the elementary pp, pn and πN reactions despite of different assumptions on quantities like the excitation function of the ∆ multiplicity, where solid experimental constraints are not available. Taking these data on elementary collisions as input, the three models provide a good description of the presently available heavy ion data. In particular, we confirm the experimentally observed enhancement of the dilepton yield (normalized to the multiplicity of neutral pions N π 0 ) in heavy-ion collisions with respect to that measured in N N = (pp + pn)/2 collisions. We identify two contributions to this enhancement: a) the pN bremsstrahlung which scales with the number of collisions and not with the number of participants, i.e. pions; b) the dilepton emission from intermediate ∆'s which are part of the reaction cycles ∆ → πN ; πN → ∆ and N N → N ∆; N ∆ → N N . With increasing system size more generations of intermediate ∆'s are created. If such ∆ decays into a pion, the pion can be reabsorbed, however, if it decays into a dilepton, the dilepton escapes from the system. Thus, experimentally one observes only one pion (from the last produced ∆) whereas the dilepton yield accumulates the contributions from all ∆'s of the cycle. We show as well that the Fermi motion enhances the production of pions and dileptons in the same way. Furthermore, employing the off-shell HSD approach, we explore the influence of in-medium effects like the modification of self-energies and spectral functions of the vector mesons due to their interactions with the hadronic environment. We find only a modest influence of the in-medium effects on the dilepton spectra in the invariant mass range where data with small error bars exist.

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“…The figure is taken from Refs. [244,245,246,247,243]. mass spectrum that in our picture are influenced by the radiation from the sQGP: M = 2M µ − 0.6 GeV and M > 1 GeV.…”

Section: Sps Energiesmentioning

confidence: 70%

“…43. Including the partonic dilepton sources allows to reproduce in PHSD the m Tspectra as well as the finding of the NA60 Collaboration [243,244,245,246,247] that the effective temperature of the dileptons (slope parameters) in the intermediate mass range is lower than that of the dileptons in the mass bin 0.6 < M < 1 GeV, which is dominated by hadronic sources (cf. Fig.…”

Section: Sps Energiesmentioning

confidence: 85%

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Effective QCD and transport description of dilepton and photon production in heavy-ion collisions and elementary processes

Linnyk

Bratkovskaya

Cassing

2016

Progress in Particle and Nuclear Physics

145

108

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In this review we address the dynamics of relativistic heavy-ion reactions and in particular the information obtained from electromagnetic probes that stem from the partonic and hadronic phases. The out-of-equilibrium description of strongly interacting relativistic fields is based on the theory of Kadanoff and Baym. For the modeling of the partonic phase we introduce an effective dynamical quasiparticle model (DQPM) for QCD in equilibrium. In the DQPM, the widths and masses of the dynamical quasiparticles are controlled by transport coefficients that can be compared to the corresponding quantities from lattice QCD. The resulting off-shell transport approach is denoted by Parton-Hadron-String Dynamics (PHSD) which includes covariant dynamical transition rates for hadronization and keeps track of the hadronic interactions in the final phase. It is shown that the PHSD captures the bulk dynamics of heavy-ion collisions from lower SPS to LHC energies and thus provides a solid basis for the evaluation of the electromagnetic emissivity on the basis of the same dynamical parton propagators that are employed for the dynamical evolution of the partonic system. The production of direct photons in elementary processes and heavy-ion reactions is discussed and the present status of the photon v 2 "puzzle" -a large elliptic flow v 2 of the direct photons experimentally observed in heavy-ion collisions -is addressed for nucleus-nucleus reactions at RHIC and LHC energies. The role of hadronic and partonic sources for the photon spectra and the flow coefficients v 2 and v 3 are considered as well as the possibility to subtract the QGP signal from the experimental observables. Furthermore, the production of e + e − or µ + µ − pairs in elementary processes and A+A reactions is addressed. The calculations within the PHSD from SIS to LHC energies show an increase of the low mass dilepton yield essentially due to the in-medium modification of the ρ-meson and at the lowest energy also due to a multiple regeneration of ∆-resonances. Furthermore, pronounced traces of the partonic degrees-of-freedom are found in the intermediate dilepton mass regime (1.2 GeV < M < 3 GeV) at relativistic energies, which will also shed light on the nature of the very early degrees-of-freedom in nucleus-nucleus collisions.

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NA60 results onp_Tspectra and the ρ spectral function in In–In collisions

Cited by 20 publications

References 13 publications

Examinations of the early degrees of freedom in ultrarelativistic nucleus-nucleus collisions

Examinations of the early degrees of freedom in ultrarelativistic nucleus-nucleus collisions

System size and energy dependence of dilepton production in heavy-ion collisions at 1-2 GeV/nucleon energies

Effective QCD and transport description of dilepton and photon production in heavy-ion collisions and elementary processes

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NA60 results onpTspectra and the ρ spectral function in In–In collisions

Cited by 20 publications

References 13 publications

Examinations of the early degrees of freedom in ultrarelativistic nucleus-nucleus collisions

Examinations of the early degrees of freedom in ultrarelativistic nucleus-nucleus collisions

System size and energy dependence of dilepton production in heavy-ion collisions at 1-2 GeV/nucleon energies

Effective QCD and transport description of dilepton and photon production in heavy-ion collisions and elementary processes

Contact Info

Product

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NA60 results onp_Tspectra and the ρ spectral function in In–In collisions