Speaker
Description
Electromagnetic probes ($\gamma$, $\gamma*$) are an excellent probe to investigate strong-interaction matter under extreme conditions. Their penetrating nature not only enables e.g. temperature measurements unbiased by the collective expansion of the fireball, but also an insight to the microscopic structure of the matter under investigation. The HADES experiment has measured virtual photons in their di-electron decay channel in heavy-ion collisions as well as in proton- and pion-induced reactions in the energy range of a few GeV.
In this contribution, we emphasize multi-differential spectra and collective behavior of dilepton sources in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.42 GeV and Ag+Ag collisions at $\sqrt{s_{NN}}$ = 2.55 and 2.42 GeV and contrast them with hadronic probes at the freeze-out stage.
The exclusive $\pi^-+p \to n_\mathrm{missing}+e^++e^-$ reactions at the center-of-mass energy in the second resonance region revealed the role of the intermediary $\rho$ meson and was the first measurement of a baryon electromagnetic transition form factor in the time-like region.
It is now accompanied by the measurement in p+p reactions at $\sqrt{s}$ = 3.7 GeV and 2.65 GeV that also serves as a baseline for dilepton studies in heavy-ion collisions at facilities under construction such as FAIR.
We also give an outlook to the study of microscopic properties of the matter with low-invariant-mass and low-momentum dileptons and the sensitivity to the phase structure of baryon-dominated matter with the new HADES programme at even lower beam energies collected at the nominal and reduced values of the magnetic field.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | The HADES Collaboration |
