Search for Higgs boson production in association with another Higgs or an exotic scalar boson in the $b\bar{b}W^{+}W^{-}$ single lepton final state at $\sqrt{s}=13$ TeV with the ATLAS experiment

Abstract

A search for Higgs boson pair production where one Higgs boson decays via $H \to b \bar{b}$ and the other Higgs boson decays via $H \to WW^*\to \ell νq \bar{q}\quad (\ell=e,μ)$ is presented. This search uses the complete Run 2 data sample recorded by the ATLAS detector at the LHC from 2015 to 2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $140$ fb$^{-1}$. The analysis looks for non-resonant Higgs boson pair production assuming Standard Model dynamics. No evidence for Higgs-boson pair production is observed and an upper limit at 95% confidence level is set at 35 times the Standard Model prediction. The same selection is used to target Beyond the Standard Model theories predicting the resonant production of the heavy scalars, $X$ and $S$, with $m_X > m_S > m_H$, undergoing the process $X \to SH, S \to W^+W^-, H \to b \bar{b}$. Limits are set on the resonant $X \to SH$ production for several combinations of the two scalar's masses within the $m_X$ mass range $350-3000$ GeV and $m_S$ mass range $170-2500$ GeV.