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High Energy, Nuclear, Particle Physics
Quark Gluon Plasma In the Presence of Charged Leptons?
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[QUOTE="vanhees71, post: 6173584, member: 260864"] The nice thing of leptons (and also photons) in the context of heavy-ion collisions is that for them the medium is transparent. Thus one can neglect "final-state interactions". When produced they leave the fireball practically completely unperturbed. Thus they are the only probes of the hot and dense medium that carry information over the whole history of the fireball evolution. Of particular importance are lepton-antilepton pairs (socalled dileptons, i.e., electron-positron or muon-antimuon pairs). Their spectral shape is directly related with the in-medium autocorrelation function of the electromagnetic current of the strongly interacting matter. Among other things they thus give some hint about the spectral properties of the light vector mesons, ##\rho##, ##\omega##, and ##\phi## and the related change of their spectral properties in the context of the chiral phase transition (in the socalled "low-mass range", ie., invariant masses of the dileptons below the ##\phi## peak). In the intermediate-mass range at high collision energies (top SPS and RHIC energies, LHC) one has a unstructured piece in the spectrum (as already in the vacuum, which is given by ##\mathrm{e}^+ + \mathrm{e}^- \rightarrow \text{hadrons}##). The main sources of dileptons there are (a) thermal radiation from the QGP and (b) correlated ##\text{D}##-##\bar{\text{D}}## (and particularly at the LHC also ##\text{B}## -##\bar{\text{B}}##) decays. If one is able to subtract this open-heavy-flavor component (as was possible in the NA60 experiment on dimuons at the SPS), one has a clear signal from the QGP, and since the invariant-mass spectrum is unaffected by the Doppler-blueshift from the flow of the medium, it's a direct space-time-weighted average of the temperature reached. Already at the SPS this mean temperature is above the pseudo-critical temperature, which is a clear indication that already at the SPS a QGP has been formed. For more information, have a look at my habilitation thesis [URL unfurl="true"]https://th.physik.uni-frankfurt.de/~hees/publ/habil.pdf[/URL] For some pedagogical introduction, see my presentations prepared for some graduate-student lecture weeks in recent years: [URL]https://th.physik.uni-frankfurt.de/~hees/hgs-hire-lectweek18/index.html[/URL] [URL]https://th.physik.uni-frankfurt.de/~hees/hgs-hire-lectweek17/[/URL] [URL unfurl="true"]https://th.physik.uni-frankfurt.de/~hees/publ/graz15-1.pdf[/URL] [URL unfurl="true"]https://th.physik.uni-frankfurt.de/~hees/publ/graz15-2.pdf[/URL] [URL]https://th.physik.uni-frankfurt.de/~hees/hqm-lectweek14/index.html[/URL] [/QUOTE]
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Quark Gluon Plasma In the Presence of Charged Leptons?
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