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 root s = 13TeV 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 mu, defined as the ratio of the observed HH production rate in the HH -> ZZ* b (b) over bar -> 4 lb (b) over bar decay channel to the standard model (SM) expectation. Possible modifications of the H trilinear coupling lambda(HHH) with respect to the SM value are investigated. The coupling modifier kappa(lambda), defined as lambda(HHH) divided by its SM prediction, is constrained to be within the observed (expected) range -8.8 (-9.8) < kappa(lambda) < 13.4 (15.0) at 95% confidence level.