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Happy Birthday Higgs boson and the start of Run-3 of the LHC

Post Date:2022-07-07

Ten years ago on July 4th 2012 the ATLAS and CMS experiments announced the discovery of the Standard Model Higgs boson particle. This particle was predicted in the Higgs mechanism that was proposed in the 1960s to explain the process that give the elementary particles their masses. Francois Englert and Peter W. Higgs were awarded the physics Nobel prize in 2013 for their work on the theory of the Higgs mechanism. Since the discovery the ATLAS collaboration has made tremendous leaps in the understanding of the Higgs boson. The experiment has also observed and measured all of the main production and decay mechanisms of the Higgs boson.

This week on July 4th 2022, CERN celebrated the 10th anniversary of the Higgs boson discovery and ATLAS makes use of this opportunity to present two papers. The first paper is published in the journal Nature [1] that provides its most comprehensive overview of the Higgs boson. The results are based on the full dataset collected by the ATLAS experiment during Run-2. The measurements of the cross-section values of the main Higgs boson production processes and the decay branching ratios are shown in Figure 1. All the measurements are consistent with the Standard Model predictions.

The second paper [2] that ATLAS presented is a conference note on the measurement of the Higgs self-coupling, which in turn can provide us clues about the formation of the Universe. The self-coupling can be measured directly by studying the production of pairs of Higgs boson (HH), or indirectly from the single-Higgs production. If the measured self-coupling deviates significantly from the Standard Model prediction, this could indicate the presence of phenomena beyond the Standard Model. By combining the results from several single-Higgs production and double-Higgs production measurements, the Higgs self-coupling constant (κλ) value is excluded outside the range of -1.3 to 6.1 at 95% confidence level for the case when all couplings of the Higgs boson to the other Standard Model particles are simultaneously measured.

The results featured in these two papers made used of results from several individual analyses that ATLAS had performed on the Run-2 data. The team led by Song-Ming Wang in the Academia Sinica ATLAS group has direct contributions to a couple of these papers [3][4].

After the celebration CERN turns its attention to the start of Run-3 data taking
on July 5th 2022. The LHC machine started successfully in colliding proton beams at the center of mass energy of 13.6 TeV, which is 600 GeV higher than in Run-2 and a new highest energy record. The ATLAS detector, which underwent three years of upgrade, successfully recorded these collisions events.



Figure 1: Measurements of the (left) cross-section values of the main Higgs boson production processes and (right) the Higgs boson decay branching ratios with the full ATLAS Run-2 dataset.


Figure 2: A proton-proton collision event in the ATLAS detector at √s=13.6 TeV that was collected on the first day of the Run-3 data taking July 5th 2022.


Figure 3: ATLAS Control Room : LHC Run-3 restarted at 13.6 TeV


[1] A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery.
https://www.nature.com/articles/s41586-022-04893-w.pdf

[2] Constraining the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s=13 TeV
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2022-050/

[3] Measurements of WH and ZG production in the H->bb decay channel in pp collisions at 13 TeV with the ATLAS detector
Eur. Phys. J. C 81 (2021) 178.

[4] Search for resonant and non-resonant Higgs pair production in the bbtautau decay channel using 13 TeV pp collision data from the ATLAS detector
ATLAS-CONF-2021-030, 2021, url: https://cds.cern.ch/record/2777236

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