Dilepton Radiation from Hot Nuclear Matter and Nucleon-Nucleon Collisions
Still very little is known about the properties of excited nuclear matter in temperature and density Repions far removed from equilibrium. Such conditions are achieved in the laboratory when heavy nuclei collide at high energies. Nuclear matter, which is initially in its ground state, is first heated and compressed. A phase of cooling and decompression then follows and the system finally evolves to its asymptotic state. The final configurations of this strongly interacting many-body system have been analyzed using a variety of methods. Inclusive spectra of protons and composites have been measured1 and particle production channels have also been investigated2. At present, some promising analysis methods are liked to variables reflecting the momentum flow during the collision. These are the kinetic flow tensor3 and the transverse momentum distribution4. However, the unambiguous extraction of the nuclear equation of state from such measurements is not without technical difficulties5. Recently, much attention has been drawn to the observation of direct photon production6. The advantage of observing an electromagnetic signal from a strongly interacting many-body system is that it will travel relatively unperturbed from the production point to the detector. Depending on the angle and on the energy of the emitted quanta, this should provide information on nuclear stopping power7 and on the dynamics of baryon-baryon cascading in hot and dense nuclear matter8.
KeywordsNuclear Matter Lepton Pair Transverse Momentum Distribution4 Soft Photon Inclusive Spectrum
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