Measurement of the Higgs trilinear self-coupling from the HH -> bb̄gammagamma and ttH(gammagamma) channels with the CMS detector

This thesis presents a search for the non-resonant production of Higgs boson pairs in the final state with one Higgs boson decaying into a pair of bb̄ quarks and the other Higgs boson decaying into a pair of photons HH → bb̄γγ. The data analyzed were collected by the CMS detector in proton-proton collisions with a center-of-mass energy of 13 TeV, for a total integrated luminosity of 137 fb −1 . In the interpretation of the results, the double Higgs production processes considered are via gluon fusion (ggHH), which is the main production process, and via vector boson fusion (qqHH). The observed(expected) upper limit to the inclusive HH → bb̄γγ cross section is 0.67(0.45) fb corresponding to 7.7(5.2) times the cross section predicted by the Standard Model. Constraints on anomalous values of the Higgs coupling parameters are measured. The parameters considered are the Higgs boson trilinear self-coupling constant λ3 , the coupling constant of two Higgs bosons with two vector bosons c2V , and the Yukawa coupling of the Higgs boson with the top quark yt . The constraint on the λ3 and on the yt parameter are significantly improved through the simultaneous fit of the cross sections of the HH processes and of the associated production of the Higgs boson with a tt̄ quark pair (tt̄H), with the Higgs boson decaying in two photons. Such processes are intrinsically correlated because they both depend from the λ3 and yt constants.