Particle Physics Division

Using a range of detectors developed with the participation of the CEA, physicists at CEA-Irfu have scrutinized the region from which the gravitational wave was detected on August 17, 2017 by LIGO-VIRGO facilities. Unlike the four previous detections of waves of the same type discovered since 2015, this new vibration of space, called GW170817, is of different origin. It does not result from the fusion of two black holes but of two densest known stars, the neutron stars.
Thanks to the INTEGRAL satellite in orbit, the astrophysicists of the Department of Astrophysics-AIM Laboratory (CEA, CNRS, Univ Paris Diderot) were able to show that the wave GW170817 was accompanied by a gamma burst, a brief emission of gamma rays emitted just 2 seconds after the fusion of the two stars. By pointing in record time one of the giant telescopes of the VLT (Chile), they also participated in the study of the visible light emission that followed the fusion, showing in particular that this light was not polarized.
Physicists from the Department of Particle Physics of CEA-Irfu also analyzed the data obtained by the ANTARES experiments for neutrino and H.E.S.S. for the search for very high energy gamma rays, showing that the GW170817 wave did not provide detectable emission.

The study of this new phenomenon, never observed directly so far, offers many exciting perspectives for astrophysics as the possibility of better understanding the origin of the heavy elements of the Universe and even the ability to measure in a complete independent way the rate of expansion of the Universe.
All of these outstanding results are published in a series of articles presented in the journals Nature, Astrophysical Journal and Physical Review Letters on October 16, 2017.

For more information : see the French version

The Cherenkov Telescope Array (CTA) consortium brings together 1300 scientists from 32 countries. They have published their scientific aims in a document over 200 pages long. This is the result of several years of work, and includes contributions from approximately fifteen Irfu researchers involved in X-ray and gamma-ray observatories (Fermi, Integral, XMM-Newton, H.E.S.S., etc.).

The electronics developed by IRFU now equips the four oldest gamma-ray telescopes of H.E.S.S. (High Energy Stereoscopic System) in Namibia. Making it possible to optimize the simultaneous operation of all five H.E.S.S. telescopes, and confirming the technical choices for its successor CTA (Cherenkov Telescope Array).  

The LHC's Atlas collaboration at Cern has observed a rare process: the production of Higgs bosons in association with a top quark and top antiquark pair. This work, supervised by an Irfu researcher, opens up perspectives on the study of the Higgs mechanism that gives mass to particles.

Data collected at the LHC (Cern) were processed to provide the most accurate assessment of an asymmetry in top quark and top antiquark production. The result is that the measured value is compatible with the prediction of the standard particle model.

Physicists from IRFU have announced that no "big brother" of the Higgs boson has been detected at the ATLAS experiment at CERN's LHC. Their results rely on new analyzes with higher sensitivity.

Light-by-light scattering, predicted in 1936, was observed for the first time by the ATLAS experiment at the LHC, thanks to "ultra-peripheral" collisions of lead ions. It is of particular interest to physicists, as it is the result of interactions between a vacuum and intense electromagnetic fields.

The data collected between 2010 and 2017 by the T2K collaboration (Tokai To Kamiokande) and the reactor neutrino experiments strengthens the trend announced a year ago—neutrinos and antineutrinos have seemingly different behavior.

The new-generation liquid argon detector used in the WA105 experiment at CERN has collected its first signals. This prototype is used in preparation of the Deep Underground Neutrino Experiment (DUNE) for neutrino observations on a mass scale, which is due to start in 2026 in the USA. This research involving IRFU aims, in particular, to shed light on the origin of matter and antimatter.

After four years of study, the Luminescent Underground Molybdenum Investigation for Neutrino mass and nature (LUMINEU) collaboration has selected lithium molybdate for the manufacture of scintillating bolometers. These ultrasensitive particle detectors will be used for neutrinoless double-beta-decay searches. Should evidence of the latter be highlighted, neutrinos would merge with their antiparticle and the absolute mass of the neutrino would become accessible.

Several decades after its discovery, dark matter remains enigmatic. Researchers from IRFU have tested three models of dark matter in which the formation of large structures was modeled using supercomputing. The reconstruction of large structures from observations of quasar spectra favors the hypothesis of a standard "cold" dark matter and sets some of the strongest constraints on these invisible masses.

An international team from the Sloan Digital Sky Survey (SDSS) has carried out the first large-scale spectroscopic analysis of quasars, and was able to create a full 3D map of the universe and its large structures as it was 6 billion years ago. For now, the standard model of Cosmology, based upon Einstein's general theory of relativity, is confirmed.

The Dark Energy Spectroscopic Instrument (Desi) will analyze the light emitted by 35 million galaxies and quasars at various times in the past of the Universe and up to 11 billion years to better understand dark energy. Its move into the construction phase in 2016 crowns several years of research and development that have resulted in a solid design and a credible observation strategy. Irfu, a partner in the project from the outset, has played a key role. A look back at a year that saw the project become a reality.

A new phase begins for DESI