Observation of the Mott effect in heavy ion collisions

Abstract

Possibility of observing the Mott momentum in the distribution of the deuterons produced in the process p + n → d + γ, in the first stage of a nuclear reaction is presented. 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. The two body phase-space and a weak dependence of the cross section σ np→dγ on energy make the p + N → d + γ process important for the high energy part of the photon spectrum. The deuteron in the final state is not Pauli-blocked. If we allowed for all deuteron momenta, that process would be the dominant source of high energy photons (E γ > 30MeV). However, the process p + n → d + γ requires the existence of the bound state of the final deuteron. That means, that the deuteron momentum p d must be above the Mott momentum p Mott [2][3][4], if the influence of the surrounding nucleons is taken into account. In particular, deuterons with low momentum cannot exist at a normal nuclear density. Typically, one finds the condition p d /2 > p Mott /2 ≃ 1.2p F for the existence of a deuteron around the normal nuclear density [4].The process involving a deuteron was not previously discussed in the context of hard photon production in heavy ion reactions [5]. Thus it seems important to test the relevance of that process in a more specific way, using the d − γ correlation. The correlation to a hard photon allows us to select the deuterons from this 2-body process. Additional condition on the minimal energy of the photon or the maximal energy of deuteron allows to select the deuteron production at the early stage of a nuclear reaction. Another way of producing deuterons involves 3-body collisions [4] and it also utilizes as a basic ingredient the value of the Mott momentum. Below, we show how in a more direct way the Mott effect can be tested in heavy ion reactions using the simpler p + n → d + γ process, where both the photon and the deuteron in the final state can be detected experimentally.To understand basic elements of the production process, the d − γ correlations will be studied in a simple firstchance collision model (FCCM). 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• in the nucleus-nucleus center of mass (c.m.). In describing the p + n → d +...

Deuteron Formation in Heavy Ion Collisions Within the Faddeev Approach

“…Deuteron formation is directly related to the Nd → NNN break-up cross section. Photoinduced reactions have also been considered [4]. Because of the energies considered, pion induced reactions can be neglected.…”

Squeezing mode in nuclear collisions

“…This pressure ionisation known as the Mott transition is well established in different fields of physics [1][2][3][4]. Alternatively in a many body system the density could be increased.…”

“…When a system with bound states is exposed to a compression beyond certain values the bound states break off and decompose into their constituents. This pressure ionisation known as the Mott transition is well established in different fields of physics [1][2][3][4]. Alternatively in a many body system the density could be increased.…”

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

“…We include also the radiative capture process : pn → dγ , which can be important in the description of high energy part of the photon spectrum. This process requires the existence of bound state of final deuteron, i.e., the deuteron momentum must be above the Mott momentum if the influence of the surrounding nucleons is taken into account [7,8] . The process pn → dγ is most important at E/A ≃ 150MeV [4,8] .…”

“…This process requires the existence of bound state of final deuteron, i.e., the deuteron momentum must be above the Mott momentum if the influence of the surrounding nucleons is taken into account [7,8] . The process pn → dγ is most important at E/A ≃ 150MeV [4,8] . The decay processes : π 0 → γγ and ∆ → Nγ , which could give rise to hard photons, have been included as well.…”