The KATRIN collaboration has just recently reported a new upper limit of 0.8 eV/c2 on the mass of neutrinos. The KATRIN spectrometer also has a strong potential to search for new, so-called "sterile" neutrinos, based on a fine analysis of the tritium beta decay spectrum. The collaboration has just published its new results in Physical Review D based on the first two data campaigns acquired in 2019. This work reveals no evidence of a fourth neutrino, and KATRIN may well be a key player in clarifying the anomalies observed by some neutrino oscillation experiments over the past 20 years or so.
The KATRIN (KArlsruhe TRItium Neutrino Experiment) located at the Karlsruhe Institute of Technology (KIT) has just crossed a symbolic threshold. In a paper published in the prestigious journal Nature Physics, the collaboration reveals a new upper limit of 0.8 eV/c^2 for the mass of neutrinos. This result is of fundamental interest for both particle physics and cosmology.
At Irfu, neutrino physics is studied using different sources such as reactors, accelerators and radioactive sources.
Irfu teams have been engaged for several decades in a long quest to study the neutrino in all its aspects, to understand its place in the Standard Model of particle physics and even more, but also its contribution to the evolution of the Universe since its first moments. The traditional summer conferences organized last year were an opportunity to measure the progress made by the armada of international experiments with which our institute is working to achieve this ultimate goal. A look back at year 2021, full of lessons and promises for the future...
A new window into the deformation of nuclei has been recently opened with the realisation that nuclear collision experiments performed at high-energy colliders, such as the BNL Relativistic Heavy Ion Collider (RHIC) or the CERN Large Hadron Collider (LHC), give access to the shape of the colliding isotopes. A collaboration between high- and low-energy theorists, including researchers from IRFU, has demonstrated that quantitative information on nuclear deformations can be obtained and has shown that the isotope 129Xe appears as triaxial, i.e. a spheroid with three unequal axes. This result represents the first evidence of triaxiality in nuclear ground states attained in high-energy experiments. Moreover, it opens the way to exciting future investigations at the interface of low- and high-energy nuclear physics.
The first measurement of Short-Range Correlations (SRC) in an exotic nucleus took place in May 2022 with the Cocotier instrument at the GSI facility in Darmstadt, Germany. This experiment is a milestone in the program that was started in 2017 with a grant from the French Research Agency that allowed physicists to build a liquid hydrogen target (see previous highlight). The goal of this experiment is to test the hypothesis that nucleon can form compact pair, the so-called SRC pair. This measurement campaign allowed us to gathered experimental data for about 60 hours with 16C beam and with a 12C beam for approximately 40 more hours in order to have a reference measurement with a well-studied stable beam. The IRFU team took a major role in preparing and running of this experiment, and is now in charge of the data analysis together with MIT, TU Darmstadt and LIP Lisbon team.
The DPhN, in collaboration with the Department of Reactor Studies of Cadarache (DES) and the Institute of Particle and Nuclear Physics of Charles University in Prague (Czech Republic), studied the properties of gamma rays emitted by uranium isotopes during neutron capture reactions. Gamma-ray spectra measured at CERN's n_TOF facility were used as a test bed for nuclear reaction models and their ingredients, including the photon strength function that characterises the ability of a nucleus to emit or absorb photons. This work has enabled consistent modelling of the photon strength functions of the uranium isotopic chain (234U, 236U, 238U) and confirmed the presence of a particular oscillation mode of the nucleus shape at low excitation energy. This study was carried out as part of the PhD thesis of Javier Moreno-Soto  and the full results are published in Physical Review C .
The LISA (Laser Interferometer Space Antenna) space mission by ESA and NASA, will observe gravitational waves from space. After its launch around 2035, LISA will observe in the low frequency band of the gravitational waves spectra and will capture the signal coming from sources which are not detected yet in the high frequency band of ground-based detectors such like Virgo, LIGO, KAGRA, or GEO600. Among the new sources of gravitational waves, the most represented are the galactic binaries whose number of detections should amount several tens of thousands. The galactic binaries are double systems made of compact stars such like neutron stars or white dwarfs in different combinations. Within the low frequency band, galactic binaries are detected during inspiral, that is to say several thousand years before fusion which is detected by ground-based detectors. Therefore, the signature of effects due to structure or internal dynamics of compact stars on the gravitational waves can potentially be detected over the lifetime of the space mission. LISA will allow to understand the state of matter inside compact objects within binary systems, their deformability, or their magnetic fields through the secular evolution of the orbits. In a recent study published in Physical Review D (DOI: https://doi.org/10.1103/PhysRevD.105.124042), a team from SYRTE in Observatoire de Paris and LDE3 from DAP/IRFU at CEA, demonstrated that the effect of magnetism within galactic binary could be measured by LISA.
The dawn of a new era in astronomy has begun as the world discovers for the first time the full capabilities of the NASA/ESA/CSA James Webb Space Telescope. The telescope's first color images and spectroscopic data, which reveal a spectacular array of previously elusive cosmic features, were released on July 12, 2022.
Understanding the star formation process is a major open question in contemporary astrophysics. It is indeed the process that controls the evolution of galaxies since their birth, gradually transforming their interstellar gas into stars and enriching it with heavy elements and dust grains. It is also the formation of stars that is at the origin of the formation of planetary systems and the appearance of life. This process is however complex and still very poorly understood. It involves the understanding of a series of hydrodynamic instabilities leading to the collapse of a molecular cloud, in which gravity, magnetic field and chemistry play a central role. Moreover, the feedback, i.e. the ionizing radiation and the wind from newly formed massive stars, has the effect of destroying the rest of the molecular cloud and thus inhibiting star formation after a few million years. This feedback is a key element, but it is still insufficiently understood.
Scientists from the CosmoStat laboratory at CEA have produced within the international science collaboration UNIONS (Ultraviolet Near Infrared Optical Northern Survey) a reference catalogue of 100 million gravitationally lensed distant galaxies, one of the largest datasets ever created. This new collection is based on thousands of deep images of the northern sky captured by MegaCam, a large digital camera built at CEA, mounted on the Canada-France-Hawaii Telescope (CFHT). Three new publications present dark-matter mass maps of the cosmic web, showing how the high-density regions in these maps help measure the still poorly known properties of dark matter. In the near future these observations will provide essential support to the European space telescope Euclid. This ESA satellite mission will map the cosmic web over the entire accessible sky at an unprecedented resolution to measure the properties of the mysterious dark energy.
While type Ia supernovae are considered as highly symmetric supernovae, the explosion in a tight binary system composed of two white dwarfs revises this paradigm. An international team (Japan, Canada, France), including a researcher from the Department of Astrophysics/AIM Laboratory of CEA Paris-Saclay, publishes a study in the Astrophysical Journal that reveals that the distinctive asymmetric structures of such a supernova leave post-mortem imprints on the morphology of the ejected matter. These morphological signatures persist and are observable in the late phase of supernova remnants. These results open the possibility to identify and characterize the explosion scenario of this type of supernova.
The French teams of the ECLAIRs and MXT telescopes, instruments at the heart of the SVOM mission, experienced an important moment during March 2022. First, a general review of the two projects took place at CNES in Toulouse in front of a group of experts. This review allowed to verify that the two instruments meet the technical specifications and will be able to carry out the scientific mission. Then a series of team visits took place in the two CNES clean rooms housing the flight models of the two instruments, ECLAIRs and MXT.
On February 12, 2022, the ANTARES neutrino telescope (Astronomy with a Neutrino Telescope and Abyss environmental RESearch) put an end to its data taking started in 2007. During 15 years, thousands of neutrinos, precious elusive particles witnesses of the cataclysmic phenomena of the Universe, were detected at 2500 m in the Mediterranean abyss. The objective: find abnormal accumulations in the neutrino sky map revealing sources at the still mysterious origin of the cosmic rays, a rain of particles discovered more than a century ago. The CEA team played a leading role in the success of this project, a pioneer in multi-messenger astronomy.
IRFU scientists and the H.E.S.S. collaboration observe time-dependent particle acceleration in our Galaxy for the first time. Novae are powerful eruptions on the surface of a white dwarf in a binary star system, in which a larger star and a smaller star orbit each other. A nova creates a shock wave that tears through the surrounding medium, pulling particles with it and accelerating them to extreme energies. The H.E.S.S. high-energy gamma-ray observatory in Namibia has now been able to observe this acceleration process for the first time. Surprisingly, the detected nova seems to cause particles to accelerate at energies reaching the theoretical limit.
These results were published in Science: https://www.science.org/doi/10.1126/science.abn0567
The explosion of a star produces a shock wave that propagates at more than 5000 km/s for centuries and it is thought that these shocks are the main source of highly energetic particles called cosmic-rays. Studying the high-energy photon emission of supernova remnants allows us to probe the nature of the accelerated particles, their energy and their composition. A French team led by researchers from the Astrophysics division/AIM laboratory of CEA-Irfu at Paris-Saclay has confirmed the detection of gamma-ray emission above an energy of 100 MeV in the direction of the historic Kepler supernova remnant. Twelve years of observation from the LAT instrument onboard the NASA Fermi space telescope were needed to confirm the existence of an efficient particle acceleration in this remnant, one of the youngest in our Galaxy. The researchers have found that the gamma-ray emission most likely results from the interaction of accelerated ions with the surrounding medium but depending on the amplitude of the magnetic field, several scenario are plausible. This study has been accepted for publication in the journal Astronomy and Astrophysics.
ESA's PLATO mission has been given the green light to continue its development after a successful critical review on January 11, 2022.
PLATO, or PLANetary Transits and Oscillations of stars, is the third medium-class mission in ESA's Cosmic Vision program. Its objective is to find and study a large number of planetary systems, with a focus on the properties of Earth-like planets in the habitable zone around solar-type stars. PLATO has also been designed to study stellar oscillations through asteroseismology, which will allow precise measurement of the parameters of the planets' host stars, including their age.
The review verified the maturity of the entire space segment (the service module and the payload module), confirming the robustness of the satellite-payload interfaces and the payload development schedule. Particular emphasis was placed on the serial production of the 26 cameras, and the robustness of the development schedule for both modules. PLATO will use the 26 cameras to discover and characterize exoplanets orbiting stars similar to our Sun.
The objective of the realization of efficient compact neutron sources is to make it possible to perform neutron scattering experiments, with practically the same qualities as those carried out with neutron beam lines from research reactors of the Orphée type*.
These compact sources are obtained from a protons beam of medium-energy (3-50 MeV) and high current (100 mA) impinging on a light element target as beryllium. This interaction creates a neutron emission. In order to be used routinely, the target must be able to withstand long exposure to high irradiation without loss of performance.
at Saclay. They show that with this device it is possible to obtain the intensity of neutrons necessary to carry out a diffraction experiment in a reasonable time, demonstrating the competitiveness of such a source for neutron scattering compared to current small and medium power nuclear reactors.
*Former research reactor at Saclay, now shutdown.