Search for nonresonant Higgs boson pair production in the four leptons plus twob jets final state in proton-proton collisions at √s = 13 TeV

The first search for nonresonant production of Higgs boson pairs (HH) with one H decaying into four leptons and the other into a pair of b quarks is presented, using proton-proton collisions recorded at a center-of-mass energy of s = 13 TeV by the CMS experiment. The analyzed data correspond to an integrated luminosity of 138 fb⁻¹. A 95% confidence level upper limit of 32.4 is set on the signal strength modifier μ, defined as the ratio of the observed HH production rate in the HH→ ZZ^∗b b ¯ → 4 ℓb b ¯ decay channel to the standard model (SM) expectation. Possible modifications of the H trilinear coupling λ _HHH with respect to the SM value are investigated. The coupling modifier κ_λ, defined as λ _HHH divided by its SM prediction, is constrained to be within the observed (expected) range −8.8 (−9.8) < κ_λ < 13.4 (15.0) at 95% confidence level. [Figure not available: see fulltext.].