Scientific challenges and project framework
The COCOTIER project (for short-range COrrelations and Isotopic spin at R3B - COrrélations à COurte porTée et spin IsotopiquE à R3B) aims at studying the short-range correlations in the exotic nuclei produced by fragmentation by the radioactive ion beam factory FAIR at GSI. The short-range correlations formed by the combination between the intermediate-range attraction with the short-range repulsive term of the NN potential produce the nucleon pairing in a very compact spatial configuration (1-1.5 fm) with a large relative momentum impulse. That is the reason why these correlations may constitute a way to probe in the laboratory the short-range correlations of the nuclear interaction.
Region covered by the short-range correlation studies, as a function of the asymmetry ratio (N/Z) and of the mass number. Points in blue: JLab data; In red: estimates for the COCOTIER project.
These correlations were studied only in the region of the stable nuclei with values of the asymetry ratio between neutron and proton numbers (N/Z) close to 1 (N/Z~1-1.5): the studies were mainly carried out with a series of experiments done at electron accelerator of the Jefferson Lab, JLab (United States). These measurements are limited to stable nuclei, and they were obtained with a low statistics. The objective of the COCOTIER project is to overcome these two limitations by performing measurements at high luminosity in inverse kinematics. The study of the short-range correlations in the isotopic chain of Oxygen nuclei (14O-24O) will constitute the goal of the first experiment at the R3B facility.
For the study of these correlations, we use the mechanism of the quasi free scattering in inverse kinematics: the exotic ion beam is sent on at a proton target, and all the reaction products are detected. It is then possible to count the pair numbers, and to deduce the momentum impulse of the nucleons forming the pair. With this goal, a liquid Hydrogen target will be built at IRFU. It will be coupled to the R3B detection system. This system combines a trajectograph (Silicon tracker), the CALIFA calorimeter, the NeuLAND neutron detector, and the analysis system of the fragment residue and of the charged particles, which are emitted at forward angles and deviated by the magnetic field of GLAD, a very large acceptance dipolar magnet built at IRFU.
The COCOTIER project is funded with an ANR (project PI: IRFU, A. Corsi) starting from October 1st, 2017. The Liquid H2 target will be built at IRFU and it will be available to perform measurements at GSI, starting from June 2019. The first experiment on the short range correlations is foreseen in 2020-2021. Other experiments using the liquid H2 target built at IRFU are also foreseen starting from 2019, the scientific objectives being to study the structure and spectroscopy of exotic nuclei produced at FAIR.
Contact : IRFU, DPhN
Last update : 01/03 2018 (4181)
Structure of exotic nuclei via direct reactions
The structure group of the DPhN conducts experimental studies to determine the structure and reactions of radioactive nuclei far from the valley of stability. These nuclei of short life, unstable, radioactive, are called exotic when they develop unusual structures (large extension of matter, halo or neutron skin, shell structure with new magic numbers). The properties (nuclear size, nucleon shell occupation) can become very different from what is observed for the stable isotope (s).