Pauli blocking and medium effects in nucleon knockout reactions

We study medium modifications of the nucleon-nucleon (NN) cross sections and their influence on the nucleon knockout reactions. Using the eikonal approximation, we compare the results obtained with free NN cross sections with those obtained with a purely geometrical treatment of Pauli-blocking and with NN obtained with more elaborated Dirac-Bruecker methods. The medium effects are parametrized in terms of the baryon density. We focus on symmetric nuclear matter, although the geometrical Pauli-blocking allows for the treatment of asymmetric nuclear matter. It is shown that medium effects can change the nucleon knockout cross sections and momentum distributions up to 10% in the energy range E=50-300 MeV/nucleon. The effect is more evident in reactions involving halo nuclei.Comment: 10 pages, 9 figures, accepted for publication in Physics Review

And there was light

I discuss the use of light as a collection of real and virtual photons to study lingering questions in particle and nuclear physics.Comment: 9 pages, 5 figures, 4 tables, Invited Lecture at the Carpathian Summer School of Physics 2014, Exotic Nuclei and Nuclear/Particle Astrophysics (V), July 13-26, Sinaia, Romani

Pygmy resonances and symmetry energy

I present a brief summary of the first three decades of studies of pygmy resonances in nuclei and their relation to the symmetry energy of nuclear matter. I discuss the first experiments and theories dedicated to study the electromagnetic response in halo nuclei and how a low energy peak was initially identified as a candidate for the pygmy resonance. This is followed by the description of a collective state in medium heavy and heavy nuclei which was definitely identified as a pygmy resonance. The role of the slope parameter of the symmetry energy in determining the properties of neutron stars is stressed. The theoretical and experimental information collected on pygmy resonances, neutron skins, and the numerous correlations found with the slope parameter is briefly reviewed.Comment: 9 pages, Contribution to the special issue of EPJA on the topic "Giant, Pygmy, Pairing Resonances and related topics" dedicated to the memory of Pier Francesco Bortignon. Additional references include

Nuclear astrophysics studies with ultra-peripheral heavy-ion collisions

I describe in very simple terms the theoretical tools needed to investigate ultra-peripheral nuclear reactions for nuclear astrophysics purposes. For a more detailed account, see arXiv:0908.4307.Comment: 12 pages, 8 figures, Lecture notes presented at the 5th European Summer School on Experimental Nuclear Astrophysics, Sep. 20- 27, 2009, Santa Tecla, Sicily, Italy. AIP proceedings, to be publishe

One and Two-photon Physics with Relativistic Heavy Ions

The physics of peripheral collisions with relativistic heavy ions (PCRHI) is reviewed. One- and two-photon processes are discussed.Comment: 14 pages, Invited talk at the 17th Winter Workshop on Nuclear Dynamics, Park City, Utah, March 10-17, 200

Geometry of Borromean Halo Nuclei

We discuss the geometry of the highly quantal nuclear three-body systems composed of a core plus two loosely bound particles. These Borromean nuclei have no single bound two-body subsystem. Correlation plays a prominent role. From consideration of the $B(E1)$ value extracted from electromagnetic dissociation, in conjunction with HBT-type analysis of the two valence-halo particles correlation, we show that an estimate of the over-all geometry can be deduced. In particular we find that the opening angle between the two neutrons in $^{6}$He and $^{11}$Li are, respectively, $\theta_{nn} = {83^{\circ}}^{+20}_{-10}$ and ${66^{\circ}}^{+22}_{-18}$. These angles are reduced by about 12% to $\theta_{nn} = {78^{\circ}}^{+13}_{-18}$ and ${58^{\circ}}^{+10}_{-14}$ if the laser spectroscopy values of the rms charge radii are used to obtain the rms distance between the cores and the center of mass of the two neutrons. The opening angle in the case of $^{11}$Li is more than 20% larger than recently reported by Nakamura \cite{Nak06}. The analysis is extended to $^{14}$Be and the two-proton Borromean nucleus $^{17}$Ne where complete data is still not available. Using available experimental data and recent theoretical calculations we find, $\theta_{nn} = {64^{0}}^{+9}_{-10}$ and $\theta_{pp} = 110^{0}$, respectively.Comment: 5 pages, one figure, version to appear in PRC, Rapid Communication