Melting rho Meson and Thermal Dileptons

The pion electromagnetic form factor at finite temperature is studied using an effective chiral lagrangian that includes explicitly vector mesons. We find that in the time-like region around the rho meson resonance it decreases with increasing temperature and leads to a suppression of dilepton production from pion-pion annihilation in a hot hadronic matter. Effects on dilepton production in high energy heavy ion collisions and its relevance to the phase transition in a hot ha...

In this comment we point out several problems concerning kinematical singularities which are encountered in the calculation of the dilepton rates in {Ruppert:2004yg}. We also comment on the method introduced in {vanHees:2000bp} and further used in refs. {Riek:2004kx,Renk:2006dt,Renk:2006ax,Ruppert:2004yg}

We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb collisions at LHC. Hadronic emission in the low-mass region is calculated using in-medium spectral functions of light vector mesons within hadronic many-body theory. In the intermediate-mass region thermal radiation from the Quark-Gluon Plasma, evaluated perturbatively with hard-thermal loop corrections, takes over. An important source over the entire mass range are decays of correlated open-charm hadrons, ...

Recently the NA60 collaboration has presented high precision measurements of dimuon spectra double differential in invariant mass $M$ and transverse pair momentum $p_T$ in In-In collisions at $158 {\rm AGeV}$. While the $M$-dependence is important for an understanding of in-medium changes of light vector mesons and is $p_T$ integrated insensitive to collective expansion, the $p_T$-dependence arises from an interplay between emission temperature and collective transverse flow....

The $\rho$ spectral function at finite temperature calculated using the real-time formalism of thermal field theory is used to evaluate the low mass dilepton spectra. The analytic structure of the $\rho$ propagator is studied and contributions to the dilepton yield in the region below the bare $\rho$ peak from the different cuts in the spectral function are discussed. The space-time integrated yield shows significant enhancement in the region below the bare $\rho$ peak in the...

Assuming that rho-mesons exist in a quark-gluon plasma close to the QCD phase transition, we calculate the dilepton production rate from quark-antiquark annihilation via a rho-meson state using Vector Meson Dominance. The result is compared to the rates from direct quark-antiquark annihilation and from pion annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the quark-gluon plasma.

Low-mass dilepton spectra as measured in high-energy heavy-ion collisions are a unique tool to obtain spectroscopic information about the strongly interacting medium produced in these reactions. Specifically, in-medium modifications of the vector spectral function, which is well known in the vacuum, can be deduced from the thermal radiation off the expanding QCD fireball. This, in particular, allows to investigate the fate of the $\rho$ resonance in the dense medium, and poss...

We review the current state of research on electromagnetic probes in the context of heavy-ion collisions. The focus is on thermal photons and dileptons which provide unique insights into the properties of the created hot and dense matter. This review is intended to provide an introductory overview of the topic as well as a discussion of recent theoretical and experimental results. In particular, we discuss the role of vector-meson spectral functions in the calculation of phot...

In this talk I first discuss predictions based on QCD sum rules and on hadronic models for the properties of vector mesons in the nuclear medium. I then describe possible experimental signatures and show detailed predictions for dilepton invariant mass spectra with a special emphasis on nuclear reactions involving elementary incoming beams and nuclear targets. I will in particular illustrate that the sensitivity of pion and photon induced reactions to in-medium effects is nea...

Dilepton production in proton- and nucleus-induced reactions at SPS energies is studied in the relativistic transport model using initial conditions determined by the string dynamics from RQMD. It is found that both the CERES and HELIOS-3 data for dilepton spectra in proton-nucleus reactions can be well described by the conventional mechanism of Dalitz decay and direct vector meson decay. However, to provide a quantitative explanation of the observed dilepton spectra in centr...