This measurement is performed through determination of the total and differential cross sections of production of pairs of Higgs bosons. These cross-sections are very low: 33 pb-1 at 13 TeV, i.e. a factor of 1000 below the single Higgs production. Both this and the need to identify and reconstruct at least 4 particles in the final state make this measurement extremely difficult.
As part of the studies on the Higgs boson for the European Strategy for Particle Physics published in 2019, it was shown that the HL-LHC program (3000 fb-1 collected after 2029, corresponding to 100,000 HH produced) will make it possible to achieve an observation with a significance of the order of 4 sigma and a measurement accuracy of 50% on the auto-coupling parameter called kappa_lambda.
The group worked, within the framework of this report, on the optimization of the HH-> bbyy decay channel which has a small branching ratio (0.3%) but a clear signature coming from the decay of one of the Higgs bosons into two photons, which makes it one of the two most promising channels.
However, if the self-coupling does not conform to the Standard Model prediction, the Higgs pair production cross section may be large enough to be observable already with the data from Run 2 (140 fb-1) or Run 3 (2022-2025, 450 fb-1). If diHiggs production is not seen with this data, a limit can be placed on the rate of HH production and the magnitude of self-coupling. Last but not least, observing the coupling of the Higgs with itself remains one of the major objectives of the LHC program and ATLAS-LAPP group.
Contacts: Stéphane Jézequel, Marco Delmastro, Nicolas Berger.
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