Reaction Dynamics of Heavy Ion Collisions Studied by Hard Photon Emission

Abstract

Dedicated to the 200th Anniversary of Annalen der Physik.-Abstract. Tlic role of photons 11s n probe of heavy ion reaction dynamics is discus..ed. Experimental dtrta on tlie systems lUO + \V and 92310 + **Mo illustrate that hard photons render a time differentid information on the evolution of heavy ion collisions ranging from protonneutron brc.rnsstralilung in the initid phase to thermal emission from highly excited reaction products in the 1;ut stage of the reaction. Meuured hard photon multiplicities provide in addition a ncw approach to determine the impact parameter of heavy ion collisions. A systematics of hard photon emission prohxbilities reveals the role of tlie nucleonic Permi motion in the collision zone. Prospects for future c*.upcriments focussing on photon m d neutrnl meson production a t relativistic b o m b d i n g energies i~r e outlined. tTntorsuchungcn dcr Reaktionsdynamik yon Schwarionenreaktionen uher dio Emission hochenergetischer Photoneri lnlinltsubersiclit. Die Bedeutung von Photonen ills Sonden fur die Reaktionsdynamik voiiSchwerionenstoBcn wird diskutiert. Experimentelle Daten zu den Systemen l 6 0 + W und g2Mo -+-9 2 & I~ xeigen, daB Photonen iiber Proton-Neutron Brcmsstrahlung ~u s der Anfangsphase bis zur thcrmisclien Emission aus hochangeregten Reaktionsprodukten in der Endphase der Reaktion Aussagen zum zeitlichcn Ablauf von SchwerionenstoBcn ermoglichen. Gemessene Photonenmultiplizitten bieten zusgtzlich ein neues Verfahren zur Bestimmung des StoBparametera in Schwerionenreaktionen. Eine Systematik der Photonenemissionswahrscheinlichkeiten verdeutlicht, daB aus den Photonendaten auf die Impulsverteilung der Nukleonen in der Reaktionszone geschloesen werden kann. Ab-schlieBend werden die Perspektiven fiir zukunftige Experimente und neue physikalische Fragestel-1 ungen bei relativistischen Schwerionenstohn dargelegt.

The Δ-isobar and proton-proton bremsstrahlung

“…With the development of modern facilities to perform the necessary detailed experiments combined with more sophisticated theoretical models than were available in the past, we are now in a much better position to investigate off-shell effects. In addition to the intrinsic interest in the NNg, reaction, the observation of high energy photons produced in intermediate energy heavy ion collisions has also motivated a considerable effort to better understand the elementary NN~ process which is the main/eaction mechanism for producing hard photons in these collisions [9,10]. The weakness of the electromagnetic interaction, combined with the fact that these photons are very energetic, makes them (the photons) a clean probe of the reaction dynamics.…”

High energy γ rays fromN14+natLuke1, Vandenbosch2, Benenson3 et al. 1993Phys. Rev. C3020View full textAdd to dashboardCite

“…Finally, P" is the probability to produce a p ray per proton-neutron collision. This has been shown to have a simple projectile velocity dependence for a wide variety of systems [7,8]. This model has been able to systematize the yields of high energy p rays for a large number of systems at beam energies above 20 MeV/nucleon [7,1].…”