Correlated Strength in the Nuclear Spectral Function

Abstract

We have carried out an (e,e'p) experiment at high momentum transfer and in parallel kinematics to measure the strength of the nuclear spectral function S(k, E) at high nucleon momenta k and large removal energies E. This strength is related to the presence of short-range and tensor correlations, and was known hitherto only indirectly and with considerable uncertainty from the lack of strength in the independent-particle region. This experiment locates by direct measurement the correlated strength predicted by theory.PACS numbers: 21.10. Jx, 25.30.Fj Introduction. The concept of independent particle (IP) motion has been rather successful in the description of atomic nuclei; the shell model, based on the assumption that nucleons move, independently from each other, in the average potential created by the interaction with all other nucleons, has been able to explain many nuclear properties. This success often comes at the expense of the need to use effective operators that implicitly account for the shortcomings of the IP basis.A more fundamental approach to the understanding of nuclei has to start from the underlying nucleon-nucleon (N-N) interaction. This N-N interaction is well known from many experiments on N-N scattering, and several modern parameterizations are available. The N-N interaction exhibits a strongly repulsive central interaction at small internucleon distances, and at medium distances a strong tensor component. These features lead to properties of nuclear wave functions that are beyond what is describable in terms of an IP model. In particular, strong short-range correlations (SRC) are expected to occur.The effects of the short-range correlations were studied for systems where the Schrödinger equation can be solved for a realistic N-N interaction [1]. Very light nuclei (today up to A≤10) and infinite nuclear matter are amongst the systems where this is feasible [2,3,4]. The corresponding calculations show that in a microscopic description of nuclear systems the short-range and tensor parts of the N-N interaction have a very important, not to say dominating, influence without which not even nuclear binding can be explained.The consequences of these short-range correlations are that the momentum distributions of nucleons acquire a tail extending to very high momenta k and at the same

New properties of the high-momentum distribution of nucleons in asymmetric nuclei

“…Moreover the (e,e N ) experiments will allow to extract nuclear spectral functions, which contain additional information on the structure of SRCs, such as the correlation between the missing energy and missing momentum. One of the first measurements [26] of the nuclear spectral function at the SRC region confirmed the high potential of the (e,e N ) reactions in correlation studies.…”

Quasifree (e,e′p) reactions on nuclei with neutron excess

“…The short-range and tensor correlations, which arise from the characteristics of the bare nucleon-nucleon interaction, account for a reduction factor of at most 10%-15% [49][50][51][52][53][54]. The remaining, and larger, part of the quenching is due to long-range correlations related to the coupling between s.p.…”

Effects of nonlocal potentials on(p,d)transfer reactions

“…In addition the real potential required a more complicated non-locality than the standard Gaussian form. The final result includes an accurate representation of the nuclear charge density, spectral information including highmomentum nucleons obtained from (e, e p) data [27] in addition to all elastic scattering data up to 200 MeV. Note that since the Perey factor [17] was derived explicitly for a potential with the simple form of the Perey and Buck interaction, it cannot be easily generalized to the DOM case.…”