Mar 24, 2023
The ATLAS collaboration announced at the Moriond conference the observation of simultaneous production of four top quarks. This is one of the rarest and heaviest processes ever observed at the Large Hadron Collider (LHC). This measurement, coordinated by IRFU, allows to test the Standard Model of particle physics in its most complex predictions.
Link to the ATLAS collaboration publication
Jun 28, 2021
As part of the luminosity increase of the Large Hadron Collider (LHC), the first phase of the ATLAS experiment upgrade is coming to an end, before a restart planned for early 2022. To meet the requirements of physics in a highly radiative environment with a high particle flux, the two internal wheels of the muon spectrometer will be replaced by new devices: the New Small Wheels (NSW).
Apr 15, 2021
The muon spectrometer of the ATLAS experiment has been an important contribution of IRFU since the design, and IRFU is still in charge of the alignment today. The spectrometer plays a key role in the reconstruction of high-energy muons, the detection of which is crucial for the search of phenomena beyond the Standard Model. The spectrometer consists of about 1200 muon chambers that form a gigantic edifice 44 m long and 24 m in diameter.
Mar 10, 2021
The ATLAS detector equipped with a new charged particle tracking device for the HL-LHC.
The high luminosity phase of the LHC (HL-LHC) should enable the collection of a dataset unprecedented in the history of particle physics. In order to record these data, the Atlas detector will undergo a major upgrade. IRFU, via the Paris-Cluster in synergy with two other laboratories in Ile de France, is committed to the construction of a part of the internal tracker.
Aug 03, 2020
Photon-photon elastic scattering is a very rare phenomenon in which two real photons interact producing a new real photon pair. The direct observation of this process at high energy, impossible during decades, was done by ATLAS [1] and CMS [2] experiment at CERN between 2016 and 2019. These successes have led the two collaborations to strengthen their involvement in this new field, leading to a new measurement, currently being published by the ATLAS experiment [3].
Jun 19, 2018
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.
Jul 07, 2017
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.
Mar 18, 2015
Les collaborations ATLAS et CMS ont présenté pour la première fois leur mesure combinée de la masse du boson de Higgs, parvenant à une mesure précise à 0,2% près. Présentée lors de la 50e édition des «Rencontres de Moriond» en Italie le 17 mars 2015, cette mesure est l’une des plus précises obtenues au LHC à ce jour.
Aug 05, 2010
Paris was the first to hear about the LHC's initial physics results
The 35th International Conference on High-Energy Physics was held at the Palais des Congrès in Paris from 22 to 28 July—an opportunity for the LHC teams to present their first results. IRFU is involved in three of the four major collaborative projects that have set up their detectors at the collision points in the ring: Alice, Atlas, and CMS. Our teams have contributed in particular to some fundamental analyses for the control of the detectors, whose performance has exceeded expectations.
Dec 23, 2009
Since the accident which occurred on the LHC accelerator several days after its commissioning in 2008, the ATLAS collaboration has been impatient to observe "true" events produced at the centre of the detector, and to make the equipment function under real conditions. On 23 November, following several days of tests with a single beam, Atlas recorded its first proton-proton collisions, at the injection energy into the LHC (450 GeV per beam, i.e. 900 GeV in the centre of mass reference frame of the collision).
