Dileptons from ϱ-mesons as a fast clock for heavy-ion collisions

Heinz, Ulrich; Lee, Kang Seog

doi:10.1016/0375-9474(92)90606-k

Cited by 19 publications

(11 citation statements)

References 7 publications

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“…The "shining" method (also called time integration method) was introduced in [48] and [2] and assumes that a resonance can continuously emit dileptons over its whole lifetime. The dilepton yield is obtained by integration of the dilepton emission rate over time, taking the collisional broadening of each individual parent resonance into account:…”

Section: Shining Methodsmentioning

confidence: 99%

Production and evolution path of dileptons at energies accessible to the HADES detector

et al. 2009

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Dilepton production in intermediate energy nucleus-nucleus collisions as well as in elementary proton-proton reactions is analysed within the UrQMD transport model. For C+C collisions at 1 AGeV and 2 AGeV the resulting invariant mass spectra are compared to recent HADES data. We find that the experimental spectrum for C+C at 2 AGeV is slightly overestimated by the theoretical calculations in the region around the vector meson peak, but fairly described in the low mass region, where the data is satisfactorily saturated by the Dalitz decay of the η meson and the ∆ resonance. At 1 AGeV an underestimation of the experimental data is found, pointing that at lower energies the low mass region is not fully saturated by standardly parametrized ∆ Dalitz decays alone. Furthermore, predictions for dilepton spectra for pp reactions at 1.25 GeV, 2.2 GeV and 3.5 GeV and Ar+KCl reactions at 1.75 AGeV are presented. The study is complemented by a detailed investigation of the role of absorption of the parent particles on the corresponding dilepton yields in the regime which has so far been probed by HADES.

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Section: Shining Methodsmentioning

confidence: 99%

Production and evolution path of dileptons at energies accessible to the HADES detector

et al. 2009

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“…For the branching ratio at the meson pole mass m V we use the value from the particle data group, Γ φ→ee (m V )/Γ tot = 2.95 · 10 −4 [70]. An important difference compared to the procedure for the long-lived pseudo-scalar mesons is the assumption that the φ mesons continuously emit dileptons over their lifetime [71]. That means, we track the time of production and the decay (or absorption) of the φ and integrate over the corresponding lifetime in the particle's rest frame.…”

Section: φ Direct Decaymentioning

confidence: 99%

Dilepton production and reaction dynamics in heavy-ion collisions at SIS energies from coarse-grained transport simulations

et al. 2015

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Dilepton invariant-mass spectra for heavy-ion collisions at SIS 18 and BEVALAC energies are calculated using a coarse-grained time evolution from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. The coarse-graining of the microscopic simulations enables to calculate thermal dilepton emission rates by application of in-medium spectral functions from equilibrium quantum-field theoretical calculations. The results show that extremely high baryon chemical potentials dominate the evolution of the created hot and dense fireball. Consequently, a significant modification of the ρ spectral shape becomes visible in the dilepton invariant-mass spectrum, resulting in an enhancement in the low-mass region Mee = 200 to 600 MeV/c 2 . This enhancement, mainly caused by baryonic effects on the ρ spectral shape, can fully describe the experimentally observed excess above the hadronic cocktail contributions in Ar+KCl (E lab = 1.76 AGeV) reactions as measured by the HADES collaboration and also gives a good explanation of the older DLS Ca+Ca (E lab = 1.04 AGeV) data. For the larger Au+Au (E lab = 1.23 AGeV) system, we predict an even stronger excess from our calculations. A systematic comparison of the results for different system sizes from C+C to Au+Au shows that the thermal dilepton yield increases stronger (∝ A 4/3 ) than the hadronic background contributions, which scale with A, due to its sensitivity on the time evolution of the reaction. We stress that the findings of the present work are consistent with our previous coarse-graining results for the NA60 measurements at top SPS energy. We argue that it is possible to describe the dilepton results from SIS 18 up to SPS energies by considering the modifications of the ρ spectral function inside a hot and dense medium within the same model.However, this also means that lepton pairs from all stages of the reaction will reach the detector. Especially for a theoretical description this is a big challenge, as it demands a realistic description of the whole space-time evolution of the heavy-ion reaction and taking the various dilepton sources into account.On the experimental side several groups have undertaken the challenging task to measure dilepton spectra in heavy-ion collisions and thereby constrain the theoretical predictions. At SPS energies the NA60 Collaboration was able to measure the ρ in-medium spectral function for the first time, thanks to the high precision of the measurement [11]. The results were in line with previous CERES results [12] and found an excess in the invariant mass range from 0.2 to 0.6 GeV/c 2 . This excess can be explained by a broadening of the ρ meson inside the hot and dense medium with small mass shifts [13][14][15][16]. At RHIC, these investigations were extended to even higher collision energies with basically the same results except for less dominant baryonic effects and a larger fraction of dileptons stemming from the QGP [17,18].Still more challenging is the interpretation of the dilepton measurements, which were performed in the...

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“…The background of dileptons from ρ-decays is usually considered as undesirable in view of thermal dilepton identification. Recently it has been shown by Heinz and Lee (1992) that such dileptons may contain valuable information on the lifetime of the hadronic phase; that is why they are called "fast clocks" for heavy-ion collisions. The overall judgement is that the identification of thermal rates in the different phases is difficult but not completely unrealistic.…”

Section: Integration Over the Spacetime Historymentioning

confidence: 99%

Phase transitions in quantum chromodynamics

1996

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The current understanding of finite temperature phase transitions in QCD is reviewed. A critical discussion of refined phase transition criteria in numerical lattice simulations and of analytical tools going beyond the mean-field level in effective continuum models for QCD is presented. Theoretical predictions about the order of the transitions are compared with possible experimental manifestations in heavy-ion collisions. Various places in phenomenological descriptions are pointed out, where more reliable data for QCD's equation of state would help in selecting the most realistic scenario among those proposed. Unanswered questions are raised about the relevance of calculations which assume thermodynamic equilibrium. Promising new approaches to implement nonequilibrium aspects in the thermodynamics of heavy-ion collisions are described.

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Dileptons from ϱ-mesons as a fast clock for heavy-ion collisions

Cited by 19 publications

References 7 publications

Production and evolution path of dileptons at energies accessible to the HADES detector

Production and evolution path of dileptons at energies accessible to the HADES detector

Dilepton production and reaction dynamics in heavy-ion collisions at SIS energies from coarse-grained transport simulations

Phase transitions in quantum chromodynamics

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