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Nov 17, 2021
LHC: beams are back!

On Oct. 27, 2021, stable proton beams circulated and collided in the Large Hadron Collider at CERN for the first time since 2018.

The CMS experiment has spent the last three years preparing for the upcoming data-taking period, Run 3, which is scheduled to start in the spring of 2022. The month of October was dedicated as a special period of commissioning with the first LHC beams - essential for ensuring that CMS is ready to collect data in Run 3. This data will be used to search for new physics and make precision Standard Model measurements.

 

The first major milestone in the LHC pilot beam program was to observe beam splash events in the CMS detector, beginning on Oct. 19. When a proton beam hits a collimator upstream of the detector, it creates a beam splash, or a big spray of particles, designed to hit a large area of the detector. CMS can use this very distinct splash event, coming unmistakably from the LHC beam, to test its data-taking chain and prepare for stable beam operation.

 
LHC: beams are back!

A beam splash recorded by the CMS detector on Oct. 22, 2021. The innermost red region represents data in the electromagnetic calorimeter, the blue in the hadronic calorimeter, and the outermost region shows data in the muon chambers. Photo: CMS Experiment

LHC: beams are back!

A collision event from stable beams with pilot beams recorded by the CMS detector on Oct. 27, 2021. The image shows data collected by the tracker (yellow), electromagnetic calorimeter (red) and hadronic calorimeter (blue). The muon system is not shown. Photo: CMS Experiment

Finally, on Oct. 27, the LHC began delivering stable beams. Each beam was at the LHC injection energy of 450 GeV, resulting in a center-of-mass proton-proton collision energy of 900 GeV. Stable beams are particularly important because the high voltage in all subdetectors can be safely turned on and all systems can be tested. While the tracker high voltage cannot be turned on during beam splashes, it was during stable beam collisions.

CMS took advantage of this pilot beam period to perform important calibrations and tests. For example, timing calibrations were performed in the tracker and calorimeters, and the inclusion of GPU nodes in the High-Level Trigger was tested. Particularly notable is the inclusion of the gas electron multiplier detectors in the central CMS data-taking chain for the first time, marking a partial upgrade to the Muon system.

 

The P2IO LabEx partners involved in the CMS team will have used this 3 years technical shutdown to finalize major data analyzes, some of which have reported sightings in the Higgs boson area. More than ever, the team is ready to conduct these analyzes with the new data and contribute to advancements in the field. These advances require new technologies in order to always push our ability to reconstruct and identify rare physical processes even further. P2IO (through LLR, IJCLab and Irfu) has a central role in the pioneering developments in calorimetry with the HGCAL project, part of the emblematic HGCFC project.

 
#185 - Last update : 11/17 2021

 

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