Nucleons are social particles. Not only do they enjoy living in communities inside nuclei, but they also form couples within these communities. Indeed, one can observe protons and neutrons forming pairs inside nuclei. DPhN physicists have played a decisive role in the first measurement of such pairs of nucleons using a new method, that will pave the way to the study of these close (or short range) interactions in radioactive nuclei. The results have recently been published in Nature Physics [Pat21]. The study of these nucleon pairs in radioactive nuclei is the goal of the ANR project COCOTIER led by IRFU.
Understanding how the nuclear interaction emerges from the basic constituents of matter is one of the challenges of contemporary physics. The nuclear interaction between nucleons (proton or neutron) is seen as a manifestation of the strong force between quarks, which is mediated by the exchange of gluons and holds the nucleon together. In spite of the longstanding efforts, a unified nuclear interaction that allows predicting the properties of all nuclei does not exist yet.
Two state-of-the-art instruments, GLAD and COCOTIER, were designed and built at Irfu in the last few years and are now operational in the R3B experimental room of the GSI heavy ion accelerator (Darmstadt, Germany). Both are intended to be part of the equipment that will be used at FAIR, the new machine under construction at the GSI site. GLAD is a large acceptance spectrometer for the analysis of relativistic radioactive heavy ion beam reactions. It was installed on site in 2015 and saw the beam for the first time in the fall of 2018. In some experiments, these beams will have interacted upstream on the COCOTIER liquid hydrogen target. The latter, funded in part by the Agence Nationale de la Recherche, has just been used for the first time in an experiment in March 2021. These two pieces of equipment are key elements for measuring the properties of nuclei at the limit of nuclear stability and allow current nuclear models to evolve towards more predictive ones.
The ancients understood that heroes, like Orion with Sirius, need their faithful companion. IRFU engineers and physicists and their collaborators are no exception to the rule and have just completed the development of a modern Sirius, a key element of the super spectrometer separator (S3) under construction at GANIL. The tests having been successful and the system has been moved to GANIL for its final installation.
In Greek mythology, Sirius, Orion's faithful four-legged companion, an outstanding hunter, was transformed into a constellation and placed at his side. This famous canid also gave its name to the brightest star in the night sky. IRFU physicists have just honoured him in their own way, this time in the world of detectors.
Two “mirror” nuclei, in which the numbers of neutrons and protons are interchanged, have markedly different shapes—a finding that defies current nuclear theories. This striking result has been obtained by Irfu researchers in collaboration with an international team and has been recently published in Physics Review Letter [1] and highlighted as editor’s suggestion [2].
Since 2010 the question of the size of the proton is at the heart of a controversy between atomic physicists and hadronic physicists. Indeed, very precise measurements of atomic physics have concluded that the size of the proton is much smaller than expected, in very strong disagreement with the experiments of elastic scattering. In collaboration with the University of Perugia, a physicist from IRFU has investigated to find the reason for such a difference. The results have been published in European Journal of Physics A [3].
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Dernière mise à jour : Nov 13th, 2024
