Dec 13, 2022
Nucleons (protons or neutrons) are the constituents of the nucleus of atoms. The exploration of their internal structure is traditionally done by determining "form factors". These quantities are accessible through the study of elastic electron-proton scattering and electron-positron annihilation reactions into proton-antiproton (or the time reverse reaction of proton-antiproton annihilation into electron-positron).
May 25, 2021
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.
Dec 08, 2020
In 2016, the announcement of the first direct detection of gravitational waves opened a new window of observation to probe our universe in a new way. The LISA (Laser Interferometer Space Antenna) space observatory promoted by ESA (European Space Agency) will allow the direct detection of gravitational waves undetectable by terrestrial interferometers.
Sep 25, 2019
It is possible to trace the shape of a drum from its vibration modes. Similarly, it is possible to measure the 3D structure of the proton and access its elementary components, quarks and gluons, from observables obtained using deeply virtual Compton scattering experiments off the proton.  By studying this scattering process, we can access this geometric information. This research topic is very active and mobilizes a large international theoretical and experimental community.
Aug 07, 2019
The series of Jefferson Laboratory (USA) experiments dedicated to the measurement of electron-proton elastic scattering showed that the extracted information on the proton structure did not agree when extracted from two kinds of experiments. To reconcile these results, it was suggested that, beyond the exchange of one photon, that is the dominant mechanism, the exchange of a second photon could become important.
Nov 07, 2018
As part of the new CLAS spectrometer project for the 12 GeV electron energy upgrade of the Jefferson Lab (USA) IRFU has been conducting R&D for more than 10 years to design and build a new generation tracker, using thin and flexible MICROMEGAS detectors that are now operating with the new CLAS12 spectrometer. After one year of installation, this tracker is operational and meets the expected characteristics with more than 95% detection efficiency and a spatial resolution of less than 100μm.
Aug 31, 2018
In an article published in August 2018 in the journal Nature [1], the CLAS collaboration of Jefferson Lab (USA) reports an extensive study on short-range correlations between nucleons in different nuclei. The conclusion goes against intuition, indicating that the greater the ratio of neutrons to protons in a nucleus, the greater the speed of protons relative to neutrons.
Jun 04, 2018
An important scientific program is devoted to the three-dimensional structure of the proton in particular its elementary constituents, quarks and gluons. A new generation of experimental facilities at Jefferson Lab (US), CERN, and perhaps later on at a future electron-ion collider (EIC), should make it possible to perform proton tomography with unprecedented accuracy.
May 04, 2018
A recent theoretical study of the IRFU has overturned a dark matter mechanism claiming to explain the anomaly in the neutron lifetime. Indeed, the strong constraints, extracted from this mechanism, make it impossible to theoretically predict the neutron stars of 2 solar masses whose existence is known. This study was conducted in collaboration with physicists from the University of Adelaide in Australia, and will soon be published in the journal J. Phys. G.
Nov 14, 2017
The physicists from the Compass collaboration at Cern, which comprises a team from Irfu, have just published the results of a new measurement of the quark structure of the proton [1]. This uncommon but eagerly awaited measurement tends to confirm one of the basic assumptions of the theory of the strong interaction, the Quantum Chromodynamics (QCD).
Jan 22, 2017
The fourth dimension of the nucleon
The dynamical view of the internal structure of the nucleon is conveniently described in terms of ‘electromagnetic form factors’, that contain the information on the charge and magnetic currents created by the constituent quarks and gluons. Electron scattering allows to characterize the nuclear matter, which distribution within a radius of 1 fm (10-15 m) is far from being uniform.


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