Iza Veliscek: The search for pair production of Higgs Bosons at the ATLAS experiment

Wednesday 20 Mar 2024, 15:00 → 17:00 US/Eastern

small seminar room

Di-Higgs production has yet to be observed and given its predicted Standard Model (SM) cross-section it is not expected to be discovered by any of the current experiments. However, anomalies in the di-Higgs production could be already detected and shine a light on Beyond SM physics. The search for di-Higgs in the b ̄bb ̄b final state exploits the 126 fb−1 of pp data collected by the ATLAS detector during the Large Hadron Collider Run 2 at √s = 13 TeV with the aim to constrain the allowed parameter space of new physics at high energy. Done for the first time in an ATLAS di-Higgs analysis, the independent optimisation of the gluon-gluon fusion (ggF) and vector boson fusion (VBF) production channels not only improves the sensitivity to anomalies in the trilinear Higgs self-coupling (κλ) but also to anomalies in the barely explored HHVV coupling (κ2V). Novel analysis strategies, especially focusing on the combination of triggers and machine learning background estimation techniques have been developed. This enabled the search to cover a wider mass range of the di-Higgs system while relying on a completely data-driven background estimation. Taking a step further from setting the limits on κλ and κ2V independently, the κλ − κ2V parameter space is explored. The ggF channel is also interpreted using the Higgs and SM Effective Field Theory, the latter is the first such di-Higgs ATLAS result.

Taking a step further the combination of the three most sensitive diHiggs channels in the b ̄bb ̄b, b ̄bγγ and b ̄bτ−τ+ final states is performed, which is further joined with the single Higgs combination.  The upper bound on the diHiggs SM signal strength extracted from the diHiggs combination is 2.4 times the SM prediction. The power of the single Higgs and diHiggs combination is that it allows the consideration of a generic κλ model, where in addition to the trilinear Higgs self-coupling, the couplings of the Higgs to the top quark, bottom quark, tau lepton and vector bosons can vary. The observed (expected) 95% confidence level is measured to be −1.3 < κλ < 6.1 (−2.1 < κλ < 7.6), when the generic κλ model is fitted.

 

zoom: https://cern.zoom.us/j/65711598156?pwd=U2ZhRUZoajU2WFpGM1FoSy8zak1adz09

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