After more than two years of maintenance and upgrades to the collider and detectors, pilot tests of the LHC are underway.

Splash events (particle flows from the interaction between the beams and a collimator located upstream of the detector) have been recorded, notably by the ATLAS and LHCb experiments. The first proton frictions at the LHC injection energy (450 GeV per beam) in stable mode took place at the end of October. This allowed the two detectors to record their first data and to validate their correct operation.

The next step is the start of Run 3 in March 2022, when the LHC will increase its energy in the center of mass from 13 to 13.6 TeV.

The LHC has just started the circulation of the beams at the injection energy (2x450 GeV) in stable mode and ATLAS records these data and in particular with its liquid argon calorimeter (LAr) which has had a major update in which the CPPM team is very active. The LAr system has just transmitted for the first time data with this new readout system in its fully updated configuration and in particular to the new first level calorimetric triggering system. This is a major step towards Run 3 which will start in spring 2022.

Read more:

• https://www.cppm.in2p3.fr/web/en/research/particle_physics/index.html#ATLAS

• https://www.cppm.in2p3.fr/web/en/research/particle_physics/index.html#LHCb

• Contacts: Marlon Barbero, head of the ATLAS team ; Olivier Leroy, head of the LHCb team

The year is 9 after the discovery of the Higgs boson. Its properties are entirely measured. Well not entirely! One small coupling stills holds against the scientists.

They try to experimentally verify whether the Higgs boson couples to itself. Measuring the Higgs boson’s self-coupling would shed light on the mechanism that gives mass to the other particles and give insight about the Higgs field.

The ATLAS collaboration has just released a new result which aims to address this question by searching for pairs of Higgs bosons. This process is incredibly rare – around 1000 times more rare than the production of one Higgs boson!

Events where one Higgs boson decays to two photons and the other Higgs boson decays to two bottom quarks provide us with a powerful handle to search for Higgs pair production.

New analysis techniques to search for this rare process (only 12 of those events would have been produced at the LHC so far). This result is more than twice as powerful than the previous ATLAS one! Limits were set on how often pairs of Higgs bosons are produced, at 4.1 times the Standard Model prediction. We also set limits on Higgs pair production via the decay of a hypothetical new scalar particle.

Although this result sets the world’s best limits on the size of the Higgs self-coupling, our work is not yet done. We will need much more data to precisely measure the Higgs self-coupling and to see whether it agrees with the Standard Model prediction. The High-Luminosity upgrade of the LHC plans to deliver a dataset 20 times larger than the one we used here.

The ATLAS team at CPPM is deeply involved in the upgrade of the detector for this phase.

More information:

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2021-016/

https://atlas.cern/updates/briefing/twice-higgs-twice-challenge

https://twitter.com/ATLASexperiment/status/1377313263986298880

Contact: Marlon Barbero, ATLAS Team Leader

The LHCb experiment at CERN announced new results which, if confirmed, would suggest hints of a violation of the Standard Model of particle physics. The results focus on the potential violation of lepton flavour universality and were announced at the Moriond conference on electroweak interactions and unified theories, as well as at a seminar held online at CERN, the European Organization for Nuclear Research.

More information: https://home.cern/news/news/physics/intriguing-new-result-lhcb-experiment-cern

Contact at CPPM : Olivier Leroy, LHCb team responsible

Illustrations of the greeting card:

To accomplish its scientific commitments, the CPPM is equipped with high-performance technological equipment and manages technical platforms: the Laboratoire Sous-marin Provence Méditerranée, the High-Performance Computing platform, the Infrared plateau, the Radon plateau. Photo credit: KM3NeT Collaboration, CPPM - Camille Moirenc

KM3NeT Site

Contact: Paschal Coyle