Antiprotons

Antiprotons

One of the most fascinating quantum phenomena in Nature is the occurrence of neutron halos and neutron skins in atomic nuclei. Thick neutron skins and halos have not yet been seen in medium mass nuclei. Their study should greatly enhance our knowledge of nuclear structure and of the nuclear equation of state, intimately linked to the structure of neutron stars.

PUMA (antiProton Unstable Matter Annihilation) is a new physics program to investigate the neutron-to-proton densities at the nuclear surface for the most exotic nuclei that can be produced today. This research, funded by the ERC [1], aims at evidencing and at characterizing neutron halos and skins in medium and heavy mass nuclei. PUMA explores a new way to study radioactive nuclei produced at very low kinetic energy: the interaction of antiprotons with unstable nuclei. This approach has never been developed anywhere thus far.

PUMA is based on a new apparatus: a transportable electromagnetic trap to store antiprotons and capture them on short-lived isotopes in order to trigger annihilations and measure the resulting radiations. The PUMA methodology involves two steps. (i) The storage of antiprotons will be performed at the new AD/ELENA facility of CERN in collaboration with the GBAR collaboration. (ii) The stored antiprotons will be transported to CERN/ISOLDE where the PUMA experiment will be conducted.

Sketch of the antiproton capture and the following annihilation.
Sketch of the antiproton capture and the following annihilation.
Simulations of pion tracks following an annihilation in PUMA. Credit: A. Corsi, CEA.
Simulations of pion tracks following an annihilation in PUMA. Credit: A. Corsi, CEA

The device is to be built within an international collaboration. Most important parts are the superconducting solenoid, the trap, the ultra-high vacuum cryostat, the tracking detection system and the analysis tools and techniques.

The project begins in January 2018. The venture is just starting.

[1] ERC Consolidator Grant, PUMA, A. Obertelli (01/2018-12/2022)