Nuclear momentum distributions at high momenta and energies --- a window on dense forms of nuclear matter

[Coaching: Wim Cosyn and Jan Ryckebusch (supervisor) ]

General Context

Nuclei are prototypical examples of self-bound and strongly correlated quantum systems. Nuclear one-body and two-body momentum distributions contain the information about the nuclear ground state in the momentum space. At momenta lower than the Fermi momentum nuclear momentum distributions are reminiscent for a strongly degenerate two-component (protons and neutrons) system of Fermions. Nuclear momentum distributions also contain a fat tail: nucleons have a finite probability to adopt a momentum that is considerably larger than the Fermi momentum. Those high-momentum components can be connected with the physics of nuclei at small inter-nucleon distances. The fat tails of the momentum distribution represent about 20% of the probability distribution and are responsible for a very large fraction of the average nuclear kinetic energy [1]. The fat tails are expected to play an increasingly more important role as one faces exotic forms of nuclear matter (e.g. neutron stars). Wigner distributions (see for example [2]) can be computed from the momentum distributions and provide a direct connection between the quantum information in the coordinate and momentum space (see for example [3]). Wigner distributions are quasi-probability distributions and can become negative in restricted ranges.
Research goals of the MSc thesis

The group has recently developed a technique [1] to compute nuclear momentum distributions over the full momentum range. The technique is applicable across the nuclear range which allows us to address also nuclei with a large neutron-to-proton ratio. The technique provides an explanation [1] for recent experimental observations that found their to prestiguous journals (see [4]
(see [4] and [5]). Another result of the developed technique is that it could determine the quantum numbers of the high-momentum nucleon pairs in nuclei [6]. The goal of the MSc thesis is to compute Wigner distributions starting from momentum distributions. The Wigner distributions provide a more profound insight into the high-momentum (or short-distance) physics of nuclei. As a result of the investigations conducted in the context of the MSc thesis, it will be possible to gain a deeper insight of the isospin dependence, of the mass dependence, and of the proton-to-neutron dependence of nuclear short-distance physics. We are seeking a student with a strong interest in statistical physics, in theoretical nuclear physics and in computational physics.
Mobility in the context of the MSc thesis

The group has several research partners on this topic which facilitates research visits to other institutes.
- [1]
Jan Ryckebusch, Wim Cosyn, Sam Stevens, Corneel Casert, Jannes Nys,
*"The isospin and neutron-to-proton excess dependence of short-range correlations",*Physics Letters B792 (2019) 21-28. - [2] Wigner quasiprobability distribution on Wikipedia.
- [3] Phase-space formulation of quantum mechanics.
- [4]
*"Momentum Sharing in Imbalanced Fermi Systems"*, Science 1256785 (2014) - [5]
*"Probing high-momentum protons and neutrons in neutron-rich nuclei”*Nature 560 (2018) 617–621. - [6]
C. Colle, O. Hen, W. Cosyn, I. Korover, E. Piasetzky, J. Ryckebusch and L.B. Weinstein,
*"Extracting the Mass Dependence and Quantum Numbers of Short-Range Correlated Pairs from A(e,e'p) and A(e,e'pp) Scattering",*Physical Review C 92 (2015) 024604

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