Limited Asymmetry Dependence of Correlations from Single Nucleon Transfer

Abstract

Single nucleon pickup reactions were performed with a 18:1 MeV=nucleon 14 O beam on a deuterium target. Within the coupled reaction channel framework, the measured cross sections were compared to theoretical predictions and analyzed using both phenomenological and microscopic overlap functions. The missing strength due to correlations does not show significant dependence on the nucleon separation energy asymmetry over a wide range of 37 MeV, in contrast with nucleon removal data analyzed within the sudden-eikonal formalism. DOI: 10.1103/PhysRevLett.110.122503 PACS numbers: 24.50.+g The existence of single-particle-like modes in nuclei, near the Fermi surface, is particularly important because these are at the basis of the nuclear shell model and thus govern the low energy nuclear dynamics. Yet, they result from nontrivial many-body correlations, which affect energy ordering and filling of active orbits. Spectroscopic factors (SFs) are a unique tool to address the question of correlations as they are strictly linked to the notion of shell occupancies and can be probed using direct reaction cross section measurements [1,2]. Information for stable nuclei was formerly provided by the electromagnetic probe (e, e 0 p) [3][4][5]. Even for closed shell nuclei like 16 O or 208 Pb, a cross section reduction by 30%-40% relative to an independent-particle-based model was observed. Different origins are now well established, like short range correlations [1] and couplings to collective modes at high excitation energy [6] or to the continuum [7]. Single nucleon pickup reactions were also used for stable nuclei yielding results consistent with (e, e 0 p) measurements [8,9].For nuclei away from the valley of stability, new approaches have been developed in inverse kinematics at various incident energies, knockout and transfer reactions. From knockout reactions at intermediate energy, a reduction factor R s was deduced as the ratio between the experimental cross section and a theoretical value obtained in a sudden-eikonal approach [10]. A strong dependence was claimed for R s versus the asymmetry (difference in separation energy) ÁS ¼ ðS p À S n Þ with ¼ þ1 (À1) for proton (neutron) removal reactions, with a reduction as high as 70% for large positive ÁS values. This reduction is still not understood and was first accounted for by possible missing correlations in shell-model calculations [10]. Different conclusions were drawn from (i) the possibility of dissipative processes beyond the sudden approximation [11,12], and (ii) transfer reactions at lower incident energies showing no ÁS dependence of R s [13]. From a theoretical point of view, ab initio calculations suggest only a mild dependence of SFs on ÁS [7,14], with equal SFs found for the nucleon removals from 56 Ni [6] despite significant ÁS values (AE 9:5 MeV). Coupled-cluster calculations [7] pointed out a further decrease of proton SFs for isotopes at the neutron dripline, due to coupling to the continuum. This has the substantial effect of enhancing the dependence on...

Structure ofC14andB14from theBedoor1, Wuosmaa2, Albers3 et al. 2016Phys. Rev. C17130View full textAdd to dashboardCite

“…Away from A=12, however, the proton p 1/2 occupancy seems to change significantly, to approximately 3% of the ground-state value for 14 C [6]. In the mirror nucleus 14 O, the corresponding neutron p 3/2 occupancy measured with the 14 O(d, t) 13 O reaction agreed with with theoretical expectations [7] when a renormalization consistent with that obtained from other analyses (see [8,9]) was applied, although no direct measurement of the neutron p 1/2 occupancy was reported. This change to a more nearly closed p 3/2 subshell for A=14 was already suggested from early calculations of spectroscopic factors for transfer reactions in the 0p-shell [10].…”

Experimental study of the knockout reaction mechanism usingO14at 60 MeV/nucleon

“…Recently, the inclusive knockout reaction with very asymmetric nucleus 14 O (|∆S| = 18.6 MeV) was performed [10], and show a strong reduction of the deeply-bound neutron removal cross section. 13 N transfer reactions however indicates that no strong reduction was observed [11]. The structure of 14 O (Z = 8) could be reasonably described, as it can be reached by the ab initio calculations [12][13][14].…”

“…The neutron bound state wave function of 14 O was calculated in a Woods-Saxon potential with depth V 0 = 81.46 MeV, r 0 = 2.5 fm and a = 0.6 fm to reproduce the experimental separation energy S n = 23.2 MeV [42]. In addition, we adopted the ground-state-to-ground-state spectroscopic factor of 3.15 [10,11], which was calculated using the code OXBASH [43] with the WBT interaction in the (0 + 2)hω psd model space.…”

“…A coincidence measurement of the knockout residues and the associated decay protons was performed, which allows us to investigate the core excitation strength quantitatively using the invariant mass method. Exclusive data from this measurement, in addition with the inclusive knockout [10] and transfer [11] results using the same nucleus 14 O will provide a benchmark for direct nuclear reaction mechanisms, shedding light on the long-standing intriguing puzzle of the discrepancy between measurements and eikonalmodel predictions for knockout reaction involving deeplybound nucleons.…”

Optical model potential for deuteron elastic scattering with1p-shell nuclei

“…DA1p is found to give satisfactory reproduction to the angular distributions of deuteron elastic scattering from both stable and radiative 1p-shell nuclei. The experimental total reaction cross sections for 9 Be, 12 C and 16 O targets are found to be overpredicted by [78] 15 N 15 14.37 12.87 13.00 [79] theoretical calculations with systematic deuteron potentials, which was found to be due to the breakup cross sections of deuterons and will be further studied in a following paper. …”