Particle number fluctuations and correlations in transfer reactions obtained using the Balian-V\'en\'eroni variational principle

TL;DR

This paper employs the Balian-Véneroni variational principle within a mean-field framework to accurately compute particle number fluctuations and correlations in nuclear transfer reactions, aligning well with experimental data.

Contribution

It introduces a novel application of the BV variational principle to calculate particle number fluctuations and correlations in nuclear collisions, improving upon standard TDHF results.

Findings

Fluctuations are larger with the BV approach than with standard TDHF.

Calculated fluctuations closely match experimental data.

Proton-neutron correlations are significant, especially in exotic systems.

Abstract

The Balian-V\'en\'eroni (BV) variational principle, which optimizes the evolution of the state according to the relevant observable in a given variational space, is used at the mean-field level to determine the particle number fluctuations in fragments of many-body systems. For fermions, the numerical evaluation of such fluctuations requires the use of a time-dependent Hartree-Fock (TDHF) code. Proton, neutron and total nucleon number fluctuations in fragments produced in collisions of two 40Ca are computed for a large range of angular momenta at a center of mass energy E_cm=128 MeV, well above the fusion barrier. For deep-inelastic collisions, the fluctuations calculated from the BV variational principle are much larger than standard TDHF results, and closer to mass and charge experimental fluctuations. For the first time, correlations between proton and neutron numbers are determined within a quantum microscopic approach. These correlations are shown to be larger with exotic systems where charge equilibration occurs.