Tensor correlations in nuclei and exclusive electron scattering

Abstract

The effect of tensor nucleon-nucleon correlations upon exclusive and semiexclusive electronuclear reactions is studied. Differential cross sections for the semiexclusive 16 O(e,eЈp) and exclusive 16 O(e,eЈpn) processes are computed by explicitly evaluating the dynamical electromagnetic coupling to a tensor correlated nucleon pair. In both reaction channels the tensor correlations contribute in a very substantial way. Tensor correlations are found to generate more electronuclear strength than central Jastrow correlations do.PACS number͑s͒: 25.30. Ϫc, 21.30.Fe, 24.10.Ϫi In the history of nuclear physics, it has been notoriously difficult to detect signals that directly point towards phenomena beyond the scope of the effective mean-field theories. This holds, in particular, for the short-range correlations that reflect the remnants of the hard-core part of the nucleonnucleon (NN) force in the medium. Recently, manifestations for strongly correlated proton pairs and the existence of Jastrow-like correlations emerged from the simultaneous detection of two protons upon absorption of one ͑virtual͒ photon by an atomic nucleus ͓1,2͔. Nuclear many-body theories have produced vastly different predictions for the short-range behavior of nuclei. The ongoing exclusive A(e,eЈpp) studies are expected to provide stringent tests of these theories. The correlations probed in proton-proton knockout are predominantly the state-independent scalar ones ͑often referred to as Jastrow correlations͒ related to the hard core part of the NN force. The tensor force, which is operative at intermediate internucleon distances (Ϸ1 -2.5 fm͒, is established to be an important ingredient of the NN force in the medium and is believed to be another source of important NN correlations which go beyond the mean-field level ͓3͔. High momentum components in the deuteron wave function, for example, are ascribed to a D-state admixture and are a direct manifestation of the presence of tensor correlations in the proton-neutron system. For a long time, the tensor interaction has been established to be a rather weak but essential ingredient of the effective NN force. Despite intensive research a recent review ͓4͔ quoted its role as ''elusive.'' Earlier studies of the role played by tensor correlations in electron scattering concentrated on inclusive A(e,eЈ) response functions, for which there are many competing effects and unambiguous information on the tensor correlations, might be difficult to extract ͓5,6͔. In the near future, exclusive experiments that aim at probing both the proton-proton and proton-neutron correlations will be performed at MAMI and TJNAF. At MAMI, where central short-range correlations in nuclei are being studied with the aid of the A(e,eЈpp) reaction ͓2,7͔, highresolution A(e,eЈpn) measurements have been scheduled for the target nuclei 3 He ͓8͔ and 16O ͓9͔. These measurements will be performed at four-momentum transfers of the order Q 2 Ϸ0.05 (GeV/c) 2 . At TJNAF, on the other hand, the small distance structure of nuclei will be probe...

Quantifying short-range correlations in nuclei

“…Theoretical (e, e pn) calculations [36,41,42] have predicted that the tensor parts of the SRC are responsible for the fact that the correlated pn strength is typically a factor of 10 bigger than the correlated pp strength. Calculations indicated that the tensor correlations are strongest for pn pairs pairs with "deuteronlike" |l 12 = 0, S = 1 relative states [41,42]. Recently, the dominance of the pn correlations over pp and nn ones has been experimentally confirmed [43,44].…”

A(e⃗,e′p⃗)Bresponses: From bare nucleons to com

“…In recent years important efforts have been devoted to provide more realistic theoretical descriptions of these processes [4][5][6][7][8][9][10][11][12][13][14][15][16]. However, there are still uncertainties associated to the various ingredients that enter in the reaction dynamics: final state interactions (FSI), off-shell effects, nuclear correlations, relativistic degrees of freedom or meson exchange currents (MEC).…”

First measurements of the 16O(e, e'pn)14N reaction

“…The real photon studies of the 16 O(γ,pn) reaction [27,28] 14 N marked in figure 6 [44]. The calculations were carried out in the same super-parallel kinematics as the measurement; again these calculations predict cross sections roughly an order of magnitude smaller than the data.…”