Electromagnetic Dissociation as a Tool for Nuclear Structure and Astrophysics

Coulomb dissociation is an especially simple and important reaction mechanism. Since the perturbation due to the electric field of the nucleus is exactly known, firm conclusions can be drawn from such measurements. Electromagnetic matrix elements and astrophysical S-factors for radiative capture processes can be extracted from experiments. We describe the basic theory, new results concerning higher order effects in the dissociation of neutron halo nuclei, and briefly review the experimental results obtained up to now. Some new applications of Coulomb dissociation for nuclear astrophysics and nuclear structure physics are discussed.Comment: 10 pages, 1 figure, to appear in Proceedings of the International School on Nuclear Physics; 22nd Course: ``Radioactive Beams for Nuclear and Astro Physics'', Erice/Sicily/Italy, September 16 - 24, 200

Dirac-Brueckner Hartree-Fock Approach: from Infinite Matter to Effective Lagrangians for Finite Systems

One of the open problems in nuclear structure is how to predict properties of finite nuclei from the knowledge of a bare nucleon-nucleon interaction of the meson-exchange type. We point out that a promising starting point consists in Dirac-Brueckner-Hartree-Fock (DBHF) calculations us- ing realistic nucleon-nucleon interactions like the Bonn potentials, which are able to reproduce satisfactorily the properties of symmetric nuclear matter without the need for 3-body forces, as is necessary in non-relativistic BHF calculations. However, the DBHF formalism is still too com- plicated to be used directly for finite nuclei. We argue that a possible route is to define effective Lagrangians with density-dependent nucleon-meson coupling vertices, which can be used in the Relativistic Hartree (or Relativistic Mean Field (RMF)) or preferrably in the Relativistic Hartree- Fock (RHF) approach. The density-dependence is matched to the nuclear matter DBHF results. We review the present status of nuclear matter DBHF calculations and discuss the various schemes to construct the self-energy, which lead to differences in the predictions. We also discuss how effective Lagrangians have been constructed and are used in actual calculations. We point out that completely consistent calculations in this scheme still have to be performed.Comment: 16 pages, to be published in Journal of Physics G: Nuclear and Particle Physics, special issue

Heavy Ion Fragmentation Reactions at Energies of 35-140 MeV in a Combined Transport and Statistical Approach

Fragment formation in heavy ion collisions at low to intermediate energy is described by a combined application of transport theory of the Boltzmann type and of a statistical program for the decay of the fragments at the late stage. The transport equations are solved by simulations using the test particle method as a finite element representation of the phase space distribution. The description of experimental data is reasonable overall, but the fragment velocity distributions point to the presence of other mechanisms and the role of fluctuations

Observation of the γγ→ττ process in Pb+Pb collisions and constraints on the τ -lepton anomalous magnetic moment with the ATLAS detector

This Letter reports the observation of τ -lepton-pair production in ultraperipheral lead-lead collisions Pb + Pb → Pb ( γ γ → τ τ ) Pb and constraints on the τ -lepton anomalous magnetic moment a τ . The dataset corresponds to an integrated luminosity of 1.44     nb − 1 of LHC Pb + Pb collisions at √ s NN = 5.02     TeV recorded by the ATLAS experiment in 2018. Selected events contain one muon from a τ -lepton decay, an electron or charged-particle track(s) from the other τ -lepton decay, little additional central-detector activity, and no forward neutrons. The γ γ → τ τ process is observed in Pb + Pb collisions with a significance exceeding 5 standard deviations and a signal strength of μ τ τ = 1.0 3 + 0.06 − 0.05 assuming the standard model value for a τ . To measure a τ , a template fit to the muon transverse-momentum distribution from τ -lepton candidates is performed, using a dimuon ( γ γ → μ μ ) control sample to constrain systematic uncertainties. The observed 95% confidence-level interval for a τ is − 0.057 < a τ < 0.024