Particle Physics Division

In 2018, IRFU is participating  in a publication CUPID-0: the first array of enriched scintillating bolometers for 0νββ decay investigations which reviews a first matrix of bolometers installed in the Gran Sasso laboratory in Italy, with the objective of tracking the double beta decay without neutrino emission (0νββ) that will reveal the nature of neutrinos. This publication describes the integration of the detectors, their testing and commissioning for a first data collection that began in 2017 with the participation of IRFU and IN2P3 researchers at various stages. The test results show a very good response of the electronics and cryogenic systems. The mean value in energy resolution proves the unmatched efficiency of this technique for measuring radioactivity, which makes it possible to dissociate beta decay from alpha decay, a source of background  in this research.

The ATLAS and CMS collaborations, involving teams from CEA/IRFU and CNRS/IN2P3, announced on 4 June 2018 at the LHCP conference the direct observation of the coupling of the quark top to the Higgs boson. Studying the interaction between the Higgs boson and the heaviest elementary particle known, the quark top, is a way of investigating the effects of new physics, which must take over from the standard model.

The results of the analyses, orchestrated by IRFU/DPHP physicists, led to the observation of this rare process and are in agreement with the predictions of the standard model. In the coming years, both experiments will collect much more data and improve the accuracy of their measurements, which could reveal a deviation from the prediction of the standard model.

CMS article: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.231801
arXiv link for the ATLAS article submitted to publication : https://arxiv.org/abs/1806.00425

More than twenty years after the discovery of the acceleration of the expansion of the Universe, the nature of the physical phenomenon at the origin of this acceleration, called "dark energy", is still unknown. The current model of cosmology is based on general relativity as a theory of gravitation and establishes a theoretical prediction for the quantity of galaxies that form at a given period of the Universe. This cosmological parameter is called the growth rate of cosmic structures. It allows to test directly the gravitation theory at the scale of these large structures.

For the first time, the eBOSS multi-spectrograph mounted on the Sloan Digital Sky Survey telescope in New Mexico, allowed to measure this parameter from the distribution of spatial correlations of quasars. Quasars are among the brightest sources of light in the Universe and allow us to probe an era almost unexplored by this cosmological test, when the Universe was between 3 and 7 billion years old. The sample on which the analysis is based corresponds to 2 years of data collection and has already allowed the selection of more than 148,000 quasars. The measurements made confirm the validity of the model of cosmology based on general relativity and can also be used to constrain alternative theories of gravity.

The results were published in the Monthly Notices of the Royal Astronomical Society (P. Zarrouk et al, 2018).

The collaboration continues to acquire data with final analysis planned for the end of 2019, which will double the sample size. DPhP cosmologists are heavily involved in all stages of the eBOSS program, as well as in its successor, the DESI project located at the Kitt Peak National Observatory in Arizona, which is scheduled to begin data collection in 2020.

The ATLAS and CMS collaborations, involving teams from CEA/IRFU and CNRS/IN2P3, announced on 4 June 2018 at the LHCP conference the direct observation of the coupling of the quark top to the Higgs boson. Studying the interaction between the Higgs boson and the heaviest elementary particle known, the quark top, is a way of investigating the effects of new physics, which must take over from the standard model.

The results of the analyses, orchestrated by IRFU/DPHP physicists, led to the observation of this rare process and are in agreement with the predictions of the standard model. In the coming years, both experiments will collect much more data and improve the accuracy of their measurements, which could reveal a deviation from the prediction of the standard model.

CMS article: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.231801
arXiv link for the ATLAS article submitted to publication : https://arxiv.org/abs/1806.00425

The HESS international collaboration, to which CNRS and CEA contribute, has published the results of fifteen years of gamma ray observations of the Milky Way. Its telescopes installed in Namibia have studied populations of pulsar wind nebulae and supernova remnants, as well as microquasars, never before detected in gamma rays. These studies are supplemented by precise measurements such as those of the diffuse emission at the center of our Galaxy. The entire set of data will henceforth serve as a reference for the international scientific community. Fourteen articles, making up the largest ever set of scientific results in this field, are published on April 9, 2018 in a special issue of the journal Astronomy & Astrophysics.

The T2K collaboration, whose goal is to study and measure neutrino oscillations, is publishing new results on the interaction of neutrinos with nuclei. This study, in which the T2K group of the IRFU plays a major role, is crucial in that it allows the dominant uncertainty on the oscillation parameters to be restrained. For the first time, protons emerging from the neutrino-nucleus interaction have been characterized using new variables capable of exposing and characterizing nuclear effects.