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Register a new userRecent observation of short range nucleon correlations in nuclei and their implications for the structure of nuclei and neutron stars
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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.
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The single-particle spectrum of the two nuclei 133Sb and 101Sn is studied within the framework of the time-dependent degenerate linked-diagram perturbation theory starting from a class of onshell-equivalent realistic nucleon-nucleon potentials. These potentials are derived from the CD-Bonn interaction by using the so-called V-low-k approach with various cutoff momenta. The results obtained evidence the crucial role of short-range correlations in producing the correct 2s1d0g0h shell structure.
Universality of short range correlations has been investigated both in coordinate and in momentum space, by means of one-and two-body densities and momentum distributions. In this contribution we discuss one- and two-body momentum distributions across a wide range of nuclei and their common features which can be ascribed to the presence of short range correlations. Calculations for few-body nuclei, namely 3He and 4He, have been performed using exact wave functions obtained with Argonne nucleon-nucleon interactions, while the linked cluster expansion technique is used for medium-heavy nuclei. The center of mass motion of a nucleon-nucleon pair in the nucleus, embedded in the full two-body momentum distribution n_NN(krel,KCM), is shown to exhibit the universal behavior predicted by the two-nucleon correlation model, in which the nucleon-nucleon pair moves inside the nucleus as a deuteron in a mean-field. Moreover, the deuteron-like spin-isospin (ST)=(10) contribution to the pn two-body momentum distribution is obtained, and shown to exactly scale to the deuteron momentum distribution. Universality of correlations in two-body distributions is cast onto the one-body distribution n(k1), obtained by integration of the two-body n_NN(k1, k2): in particular, the high momentum part of n(k1) exhibits the same pattern for all considered nuclei, in favor of a universal character of the short range structure of the nuclear wave function. Perspectives of this work, namely the calculation of reactions involving light and complex nuclei with realistic wave functions and effects of Final State Interactions (FSI), investigated by means of distorted momentum distributions within the Glauber multiple scattering approach, are eventually discussed.
Atomic nuclei are complex strongly interacting systems and their exact theoretical description is a long-standing challenge. An approximate description of nuclei can be achieved by separating its short and long range structure. This separation of scales stands at the heart of the nuclear shell model and effective field theories that describe the long-range structure of the nucleus using a mean- field approximation. We present here an effective description of the complementary short-range structure using contact terms and stylized two-body asymptotic wave functions. The possibility to extract the nuclear contacts from experimental data is presented. Regions in the two-body momentum distribution dominated by high-momentum, close-proximity, nucleon pairs are identified and compared to experimental data. The amount of short-range correlated (SRC) nucleon pairs is determined and compared to measurements. Non-combinatorial isospin symmetry for SRC pairs is identified. The obtained one-body momentum distributions indicate dominance of SRC pairs above the nuclear Fermi-momentum.
We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive 4He/3He cross section ratio is observed to be both x and Q2 independent for 1.5 < x < 2, confirming the dominance of two- nucleon (2N) short-range correlations (SRCs). For x > 2, our data do not support a previous claim of three-nucleon (3N) correlation dominance. While contributions beyond those from stationary 2N- SRCs are observed, our data show that isolating 3N-SRCs is more complicated than for 2N-SRCs.
Nuclear dynamics at short distances is one of the most fascinating topics of strong interaction physics. The physics of it is closely related to the understanding the role of the QCD in generating nuclear forces at short distances as well as understanding the dynamics of the super-dense cold nuclear matter relevant to the interior of neutron stars. With an emergence of high energy electron and proton beams there is a significant recent progress in high energy nuclear scattering experiments aimed at studies of short-range structure of nuclei. This in turn stimulated new theoretical studies resulting in the observation of several new phenomena specific to the short range structure of nuclei. In this work we review recent theoretical and experimental progress in studies of short-range correlations in nuclei and their importance for advancing our understanding of the dynamics of nuclear interactions at small distances.
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