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...

Expérience GANIL/SPIRAL/MUST2/E525SThe low-lying spectroscopy of 6He was investigated via the 2-neutron transfer reaction p(8He, t) with the 8He beam delivered by the SPIRAL facility at 15.4 A MeV. The light charged particles produced by the direct reactions were measured using the MUST2 Si-strip telescope array. Above the known 2+ state, two new resonances were observed: at E∗ = 2.6±0.3 MeV (width Γ = 1.6±0.4 MeV) and at 5.3±0.3 MeV with Γ = 2 ± 1 MeV. Through the analysis of the angular distributions, they correspond to a 2+ state and to an L = 1 state, respectively. These new states, challenging the nuclear theories, could be used as benchmarks for checking the microscopic inputs of the newly improved structure models, and should trigger development of models including the treatments of both core excitation and continuum coupling effects

Energies and spectroscopic factors of the first 7=2 − , 3=2 − , 1=2 − , and 5=2 − states in the 35 Si 21 nucleus were determined by means of the (d, p) transfer reaction in inverse kinematics at GANIL using the MUST2 and EXOGAM detectors. By comparing the spectroscopic information on the 35 Si and 37 S isotones, a reduction of the p 3=2 -p 1=2 spin-orbit splitting by about 25% is proposed, while the f 7=2 -f 5=2 spin-orbit splitting seems to remain constant. These features, derived after having unfolded nuclear correlations using shell model calculations, have been attributed to the properties of the two-body spin-orbit interaction, the amplitude of which is derived for the first time in an atomic nucleus. The present results, remarkably well reproduced by using several realistic nucleon-nucleon forces, provide a unique touchstone for the modeling of the spin-orbit interaction in atomic nuclei. Introduction.-The spin-orbit (SO) interaction, which originates from the coupling of a particle spin with its orbital motion, plays an essential role in quantum physics. In atomic physics it causes shifts in electron energy levels due to the interaction between their spin and the magnetic field generated by their motion around the nucleus. In the field of spintronics, spin-orbit effects for electrons in materials [1] are used for several remarkable technological applications. In atomic nuclei, the amplitude of the SO interaction is very large, typically of the order of the mean binding energy of a nucleon. It is an intrinsic property of the nuclear force that must be taken into account for their quantitative description.An empirical one-body SO force was introduced in atomic nuclei in 1949 [2] to account for the magic numbers and shell gaps that could not be explained otherwise at that time. In this framework each nucleon experiences a coupling between its orbital momentum l⃗ and intrinsic spin ⃗ s. This ls coupling is attractive for nucleons having their orbital angular momentum aligned with respect to