Subthreshold Pion Dynamics as a Source for Hard Photons beyond Proton-Neutron Bremsstrahlung in Heavy-Ion Collisions

Abstract

We report on the study of extremely high energy photons, pions and etas, produced in intermediate energy heavy-ion collisions. Possibility of imaging the final-state phase space in these collisions by the Bose-Einstein correlations for photons is critically examined.

Observation of the Mott effect in heavy ion collisions

“…These can form background pairs either with a correlated γ or deuteron, or with themselves. The bremsstrahlung of photons is known to take place at very low rates for high energy photons [1,9], comparable to the rates of production for the d − γ channel. This 2 The Mott condition (1) implies that the deuterons are mostly emitted in the direction of c.m.…”

“…The correlation of a hard photon with a deuteron allows to select those deuterons produced at the beginning of a reaction.PACS numbers: 25., 25.90.+k, 25.70.Lm Corresponding author : M. Ploszajczak GANIL, BP 5027 F-14076 Caen Cedex 05 France * E-mail : bozek@solaris.if j.edu.pl 1 Recent analysis of the hard photon production in heavy ion collisions shows the importance of the two-body process π + N → N + γ in the description of the high energy part of the photon spectrum observed experimentally by the TAPS collaboration [1]. The inclusion of the processes p + n → d + π and p + n → d + γ seems to be necessary in order to improve, simultaneously, the description of the data for the pion and photon production.…”

“…Recent analysis of the hard photon production in heavy ion collisions shows the importance of the two-body process π + N → N + γ in the description of the high energy part of the photon spectrum observed experimentally by the TAPS collaboration [1]. The inclusion of the processes p + n → d + π and p + n → d + γ seems to be necessary in order to improve, simultaneously, the description of the data for the pion and photon production.…”

“…The photon spectrum obtained in correlation with a deuteron can be compared to the total photon yield in order to show directly which part of the spectrum is due to the photons produced in the d− γ channel. This channel of hard photon production is important especially at energies above 140MeV [1] . Finally, it should be noted that the absorption of the deuterons is quite substantial, unlike for the absorption of photons.…”

“…In this model of the initial phase of a heavy ion reaction, the initial momentum distribution of nucleons, that limits the deuteron momenta, is given by the two Fermi spheres 1 . For that distribution, the deuterons are emitted predominantly at 90…”