Particle Physics Division

The GBAR Collaboration gathers around 50 members from 17 Institutes, with the goal of measuring the acceleration of hydrogen antiatoms in the Earth gravitational field.  The experiment has been installed at CERN at the AD-ELENA ring.

It produced its first antihydrogen beam in 2022: P. Adrich et al., Eur. Phys. J. C 83, 1004 (2023).

SPP physicists are at the origin of the GBAR project.  Specifically the SPP group has initially developed a novel high-intensity source of positrons, based on an electron linac, managed to store these positrons in a Penning trap, and to produce positronium from their interactions with a porous SiO2 substrate.

The H.E.S.S. Collaboration gathers more than 170 scientists from 32 institutes of 12 countries. Four 12 m-telescopes, installed since 2002 in Namibia, are in operation to observe Cherenkov light produced by interaction of high-energy gamma rays with the upper atmosphere.  Since 2012, a fifth telescope of 28 m-diameter completes the network (H.E.S.S.-2).  H.E.S.S. observations have allowed the discovery of more than a hundred gamma ray sources.  The CTA project, which will encompass about a hundred telescopes of various sizes (6, 12 and 24 m in diameter) in the southern hemisphere, and about thirty in the northern hemisphere, is being put in place. 

The SPP group has contributed to the H.E.S.S.-2 level-2 trigger development, and concentrates on the indirect search for dark matter or exotic particles in the spectra of observed objects, in particular the Galactic center. In CTA, the group participates and supervises the development of a camera (Nectarcam) for middle-size telescopes, and contributes to the design and production of mirrors. 

The ATLAS Collaboration gathers close to 3,000 physicists, from 174 institutes in 38 countries.  ATLAS is one of the two general-purpose experiments at the CERN Large Hadron Collider (LHC). ATLAS has recorded proton-proton collision data at 7 TeV center-of-mass energy in 2010 and 2011, then at 8 TeV in 2012 (Run 1). The Higgs boson discovery was announced at CERN in July 2012. The Run 2 of the LHC, which started in 2015 at 13 TeV energy, is on going until end of 2018.  

The ATLAS group at IRFU has contributed to the design and construction of the muon spectrometer and the liquid Argon electromagnetic calorimeter.  The group is active in data analysis: properties of the Higgs boson, tests of the Standard Model, and search for physics beyond the Standard Model.  IRFU physicists are also involved in the upgrades of the ATLAS detector for the high-luminosity phases of the LHC, in particular they are building part of a novel forward muon detector known as NSW (New Small Wheels) and improving the trigger capabilities of the electromagnetic calorimeter.

The CMS Collaboration gathers close to 2,500 physicists, from 180 institutes in 43 countries.  CMS is one of the two general-purpose experiments at the CERN Large Hadron Collider (LHC). CMS has recorded proton-proton collision data at 7 TeV center-of-mass energy in 2010 and 2011, then at 8 TeV in 2012 (Run 1). The Higgs boson discovery was announced at CERN in July 2012. The Run 2 of the LHC, which started in 2015 at 13 TeV energy, is on going until end of 2018.   CMS has recorded more data in 2016 than during Run-1.

IRFU engineers have designed the CMS magnet, which is the largest supraconducting solenoidal magnet in the World : 6 m in diameter, 12 m long, yielding a 3.8 T homogeneous and uniform magnetic field in the detection volume, which corresponds to more than 2 GJ of stored magnetic energy. 

The CMS group at IRFU has participated to the design and construction of the electromagnetic calorimeter, and in particular of the laser system to monitor the transparency of the crystals.  The group is active in data analysis: Standard Model physics, study of the Higgs boson, search for non-standard physics.

The T2K Collaboration gathers about 500 physicists from 59 institutes in 11 countries.  T2K is a longue-baseline off-axis neutrino experiment for the study of neutrino oscillations using a beam of muonic neutrinos produced at the J-PARC Japanese facility, and measured at short distance (280 m) by the ND280 detectors and at large distance (295 km) by the Super Kamiokande water-Cherenkov detector.   The data taking started in 2009 and will extend until 2020.

The Irfu group has participated to the design and construction of the set of three large TPCs of the near detector ND280, and is involved in data analysis of both near and far detectors. The group is noticeably interested in precise measurements of neutrino interaction cross sections on various targets, with the goal of reducing systematic uncertainties in oscillation parameter measurements.  Following a major involvement in the design studies for the next generation long-baseline experiments in the context of the European LAGUNA-LBNO project, the group now participates to the construction of the dual-phase liquid argon prototype WA105 at CERN, whose aim is to validate the technology for the far detector of the long baseline project DUNE (Deep Underground Neutrino Experiment) in the US.

The group shows interest in the new phase of the T2K experiment, with a more intense neutrino beam from J-PARC to Super Kamiokande, and more performing near detectors. The groupe entertains close links with the Hyper Kamiokande project, a megaton-scale water-Cherenkov detector that could take over Super Kamiokande and give access to a significant observation of CP violation in the leptonic sector using neutrinos from J-PARC. 

Physicists of the SPP Cosmology group use several cosmological probes to constrain the energy content of the Universe: the baryon acoustic oscillation (BAO), with participation to the BOSS, eBOSS, and DESI experiments ; type 1A supernovae within the SNLS experiment ; and galaxy clusters with the data of the Planck satellite.

The BAO studies exploit quasars, with which one can explore distant regions (with redshifts between 1 and 3), by looking at the Lyman-α, which map the intergalactic hydrogen clouds through which the emitted light is travelling. The BOSS project of the SDSS-III (Sloan Digital Sky Survey) has ended data taking, to allow for eBOSS of the SDSS-IV to begin.  The DESI project will start taking data at the turn of 2020.  The Institute is responsible for the production of the cryostats for the ten triple-spectrometers of DESI. 

The SNLS activities are focused on the photometric study of SN1A, and the investigation of the galileon hypothesis, in collaboration with physicists of the CMS group.

As for the Planck data, the SPP group takes responsibility for producing a catalog of galaxy clusters, in close collaboration with groups of the SAp and the APC laboratory.

The International Linear Collider (ILC) is one of the collider projects envisioned as the next large machine for particle physics, and the in-depth study of the electroweak symmetry breaking sector. 

The ILC is a linear electron-positron collider located in Japan, whose physics programme spans several decades, starting around 2030.  In a first phase the ILC will operate at an collision energy of 250 GeV, for the precise study of the properties of the Higgs boson produced in association with a Z boson.  In subsequent phases, the energy will be pushed to 360 GeV, for precise measurements of the top quark at the pair production threshold, the at 500 GeV and above, for the study of the Higgs boson produced by vector boson fusion and the Higgs boson pair production. The ILC displays a strong discovery potential and is complementary to the HL-LHC in terms of sensitivity to the physics beyond the Standard Model. 

In the past fifteen years, Irfu engineers have played a key role in the selection of the cryogenic acceleration technology for the ILC. Recently, in the context of the XFEL project at DESY in Germany, Irfu and its partners have demonstrated the production and assembly of a large number of cryomodules presenting the accelerating fields that are required for an ILC (above 25 MV/m).

The detector R&D led at Irfu for the ILD experiment at the ILC is focused on the development of a TPC tracking detector with a micro-pattern gas detector (MPGD) readout.  The considered MPGD is Micromegas, a technology that was initiated by Irfu physicists and engineers.   

The RD51 Collaboration at CERN, in which Irfu physicists have a leadership role, is a R&D effort devoted to the development of the MPGD technology for particle physics detectors at future colliders. 

CaLIPSO is a medical imaging project aiming at a breakthrough in high-spatial-resolution Positron Emission Tomography (PET).  The CaLIPSO concept for the detection of 511 keV gamma rays is based on the precise 3D localisation of the photoelectron in an organometallic liquid, associated with ultra fast electronics.  This detector R&D activity is on-going at IRFU since 2009, with very promising results. 

The Double-Chooz collaboration gathers about 160 physicists and engineers from 38 Institutes in 8 countries. Located next to the Chooz nuclear plant in the French Ardennes, the experiment is designed to study neutrino oscillations from the flux of electronic antineutrinos emitted from the two nuclear reactors of the plant. Compared to previous generation reactor neutrino experiments, Double-Chooz uses two detectors rather than one, in order to reduce normalisation uncertainties.  One of the detectors is located about 1 km from the cores, while the second one is at about 400 m.  

First results with only the far detector were presented in November 2011, showing evidence for an non-zero value of the θ₁₃ mixing angle.   In 2016, the Collaboration presented for the first time results based on the analysis of data from the two detectors. The comparison of rates and energy spectra of electronic antineutrinos recorded by the two detectors, which are as alike as they can be, allows a significant reduction of the systematic uncertainties in the measurement of the parameter sin²(2θ₁₃) that governs the oscillation of the electronic flavour to another flavour at short distance.  The obtained value is significantly different from zero with a relative precision of 15%, in agreement with the even more precise result by the Daya Bay experiment, in China. The fact that mixing angle θ₁₃ could be measured non-zero with such precision is one of the most striking neutrino physics results in recent years.

In addition, Double Chooz has produced a measurement of the reactor neutrino cross section, irrespective of the oscillation phenomenon, with a relative precision of de 1.2%. This measurement is key to the understanding of the reactor neutrino anomaly, which was revealed by Irfu physicists in 2011.  The reactor neutrino anomaly has to do with a systematic deficit of the measured flux of antineutrinos compared to the calculated ones, by the most sophisticated models of antineutrino production in the core of nuclear reactors.  One of the proposed hypotheses to solve the anomaly is the existence of a fourth flavour of sterile neutrinos.

Irfu physicists and engineers were at the origin of the Double-Chooz experiment. They have been in charge of the technical coordination, as well as of the design and construction of the various acrylic vessels.  The groups has put in place the measurement of the mass of the liquids involved, and has performed compatibility tests for all the materials.  SPP physicists are main players in the data analysis and the production of scientific results.

The Double-Chooz experiment will be decommissioned in 2018.  

The Nucifer experiment, installed next to the research reactor Osiris at Saclay, was designed to follow the fuel cycle in the core of reactors from the measurement of the flux of antineutrinos, and consequently to provide a tool to survey nuclear plants for non-proliferation purposes. The techniques involved in Nucifer to measure the flux of antineutrinos very close from the core of a reactor have paved the way to the data analysis in Double Chooz.

The CeSOX experiment proposes to position an intense radioactive source of Cerium 144 known as CeANG (for Cerium Antineutrino Generator) beneath the Borexino neutrino detector at the Gran Sasso Laboratory, next to L'Aquila in Italy.  The CeANG source is being produced by the P. A. Mayak Company in Russia, and will be delivered early in 2018.  The scientific goal of the CeSOX experiment is to demonstrate the existence of a fourth flavour of sterile neutrinos that would elucidate the reactor neutrino anomaly (see above), or to exclude its existence in a significant region of the parameter space.