Particle Physics Division

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 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.

What is the mass of neutrinos? To answer this fundamental question, the KATRIN experiment was designed and built by an international collaboration at the Karlsruhe Institute of Technology. On June 11, 2018, an international symposium marked the beginning of data acquisition. The first electron spectra from tritium decay have been analyzed with an analysis chain developed at IRFU. Everything conforms to the required specifications and the first long data taking campaign for physics can start.  First results expected in 2020.