Recent observation of short range nucleon correlations in nuclei and their implications for the structure of nuclei and neutron stars

TL;DR

This paper provides experimental evidence for short-range correlations in nuclei, discusses their implications for nuclear structure and neutron star cooling, and highlights the role of tensor forces and QCD in these phenomena.

Contribution

It presents unambiguous experimental evidence for SRCs, quantifies their prevalence, and explores their impact on nuclear and neutron star physics, including modifications to theoretical models.

Findings

Nearly all nucleons with momenta ≥ 300 MeV/c are in SRCs.

Probability of SRCs in medium/heavy nuclei is about 25%.

SRCs influence neutron star cooling and require theoretical model adjustments.

Abstract

Novel processes probing the decay of nucleus after removal of a nucleon with momentum larger than Fermi momentum by hard probes finally proved unambiguously the evidence for long sought presence of short-range correlations (SRCs) in nuclei. In combination with the analysis of large $Q^2$, A(e,e')X processes at $x>1$ they allow us to conclude that (i) practically all nucleons with momenta $\ge$ 300 MeV/c belong to SRCs, consisting mostly of two nucleons, ii) probability of such SRCs in medium and heavy nuclei is $\sim 25%$, iii) a fast removal of such nucleon practically always leads to emission of correlated nucleon with approximately opposite momentum, iv) proton removal from two-nucleon SRCs in 90% of cases is accompanied by a removal of a neutron and only in 10% by a removal of another proton. We explain that observed absolute probabilities and the isospin structure of two nucleon SRCs confirm the important role that tensor forces play in internucleon interactions. We find also that the presence of SRCs requires modifications of the Landau Fermi liquid approach to highly asymmetric nuclear matter and leads to a significantly faster cooling of cold neutron stars with neutrino cooling operational even for $N_p/N_n \le 0.1$. The effect is even stronger for the hyperon stars. Theoretical challenges raised by the discovered dominance of nucleon degrees of freedom in SRCs and important role of the spontaneously broken chiral symmetry in quantum chromodynamics (QCD) in resolving them are considered. We also outline directions for future theoretical and experimental studies of the physics relevant for SRCs.