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Register a new userDiffraction on nuclei: effects of nucleon-nucleon correlations and inelastic shadowing within an improved Glauber-Gribov approach
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Authors
Claudio Ciofi degli Atti
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The importance of the effects of nucleon-nucleon (NN) short-range correlations (SRC) and Gribov inelastic shadowing (IS) on various high energy scattering processes involving nuclear targets is demonstrated within an improved Glauber-Gribov approach.
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Different types of high-energy hadron-nucleus cross sections are discussed emphasizing the role played by Nucleon-Nucleon (NN) Short-Range Correlations (SRC) and Gribov Inelastic Shadowing (IS)
This article reviews our current understanding of how the internal quark structure of a nucleon bound in nuclei differs from that of a free nucleon. We focus on the interpretation of measurements of the EMC effect for valence quarks, a reduction in the Deep Inelastic Scattering (DIS) cross-section ratios for nuclei relative to deuterium, and its possible connection to nucleon-nucleon Short-Range Correlations (SRC) in nuclei. Our review and new analysis (involving the amplitudes of non-nucleonic configurations in the nucleus) of the available experimental and theoretical evidence shows that there is a phenomenological relation between the EMC effect and the effects of SRC that is not an accident. The influence of strongly correlated neutron-proton pairs involving highly virtual nucleons is responsible for both effects. These correlated pairs are temporary high-density fluctuations in the nucleus in which the internal structure of the nucleons is briefly modified. This conclusion needs to be solidified by the future experiments and improved theoretical analyses that are discussed herein.
By analyzing recent microscopic many-body calculations of few-nucleon systems and complex nuclei performed by different groups in terms of realistic nucleon-nucleon (NN) interactions, it is shown that NN short-range correlations (SRCs) have a universal character, in that the correlation hole that they produce in nuclei appears to be almost A-independent and similar to the correlation hole in the deuteron. The correlation hole creates high-momentum components, missing in a mean-field (MF) description and exhibiting several scaling properties and a peculiar spin-isospin structure. In particular, the momentum distribution of a pair of nucleons in spin-isospin state $(ST)=(10)$, depending upon the pair relative ($k_{rel}$) and center-of-mass (c.m.) ($K_{c.m.}$) momenta, as well as upon the angle $Theta$ between them, exhibits a remarkable property: in the region $k_{rel}gtrsim 2,fm^{-1}$ and $K_{c.m.}lesssim 1,fm^{-1} $, the relative and c.m. motions are decoupled and the two-nucleon momentum distribution factorizes into the deuteron momentum distribution and an A-dependent momentum distribution describing the c.m. motion of the pair in the medium. The impact of these and other properties of one- and two-nucleon momentum distributions on various nuclear phenomena, on ab initio calculations in terms of low-momentum interactions, as well as on ongoing experimental investigations of SRCs, are briefly commented.
A new linked cluster expansion for the calculation of ground state observables of complex nuclei with realistic interactions has been developed [1-3]; using the V8 potential [4] the ground state energy, density and momentum distribution of complex nuclei have been calculated and found to be in good agreement with the results of [5], obtained within the Fermi Hyper Netted Chain, and Variational Monte Carlo [6] approaches. Using the same cluster expansion, with wave function and correlations Realistic Calculation of the Effects of Nucleon-Nucleon Correlations in High-Energy Scattering Processes Off Nuclei parameters fixed from the calculation of the ground-state observables, the semi-inclusive reaction of type A(e,ep)X has been calculated taking final state interaction effects into account within a Glauber type calculation as in Ref. [7]; the comparison between the resulting distorted and undistorted momentum distributions provides an estimate of the transparency of the nuclear medium to the propagation of the hit proton. The effect of color transparency has also been considered within the approach of [8,9]; it is shown that at high values of Q^2 finite formation time effects strongly reduce the final state interaction, consistently with the idea of a reduced interaction of the hadron produced inside the nucleus [10]. The total neutron-nucleus cross section at high energies has also been calculated [11] by considering the effects of nucleon-nucleon correlations, which are found to increase the cross section by about 10% in disagreement with the experimental data. The inclusion of inelastic shadowing effects of Refs. [12,13] decreases back the cross section, leading to a good agreement between experimental data and theoretical calculations.
Energy-dependent and single-energy fits to the existing nucleon-nucleon database have been updated to incorporate recent measurements. The fits cover a region from threshold to 3 GeV, in the laboratory kinetic energy, for proton-proton scattering, with an upper limit of 1.3 GeV for neutron-proton scattering. Experiments carried out at the COSY-WASA and COSY-ANKE facilities have had a significant impact on the partial-wave solutions. Results are discussed in terms of both partial-wave and direct reconstruction amplitudes.
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