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

A generalized method to calculate the excitation-energy dependent parity ratio in the nuclear level density is presented, using the assumption of Poisson distributed independent quasi particles combined with BCS occupation numbers. It is found that it is crucial to employ a sufficiently large model space to allow excitations both from low-lying shells and to higher shells beyond a single major shell. Parity ratios are only found to equilibrate above at least 5-10 MeV of excitation energy. Furthermore, an overshooting effect close to major shells is found where the parity opposite to the ground state parity may dominate across a range of several MeV before the parity ratio finally equilibrates. The method is suited for large-scale calculations as needed, for example, in astrophysical applications. Parity distributions were computed for all nuclei from the proton dripline to the neutron dripline and from Ne up to Bi. These results were then used to recalculate astrophysical reaction rates in a Hauser-Feshbach statistical model. Although certain transitions can be considerably enhanced or suppressed, the impact on astrophysically relevant reactions remains limited, mainly due to the thermal population of target states in stellar reaction rates.

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We studied the reaction 12 C(e,e'p) in quasielastic kinematics at momentum transfers between 0.6 and 1.8 (GeV/c) 2 covering the single-particle region. From this the nuclear transparency factors are extracted using two methods. The results are compared to theoretical predictions obtained using a generalization of Glauber theory described in this paper. Furthermore, the momentum distribution in the region of the 1s-state up to momenta of 300 MeV/c is obtained from the data and compared to the Correlated Basis Function theory and the Independent-Particle Shell model.

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