Search for exotic decays of the Higgs boson into b $\overline{b}$ and missing transverse momentum in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for the exotic decay of the Higgs boson (H) into a b $\overline{b}$ resonance plus missing transverse momentum is described. The search is performed with the ATLAS detector at the Large Hadron Collider using 139 fb −1 of pp collisions at $\sqrt{s}$ = 13 TeV. The search targets events from ZH production in an NMSSM scenario where H → ${\stackrel{~}{\chi }}_{2}^{0}{\stackrel{~}{\chi }}_{1}^{0}$ , with ${\stackrel{~}{\chi }}_{2}^{0}$ → $a{\stackrel{~}{\chi }}_{1}^{0}$ , where a is a light pseudoscalar Higgs boson and ${\stackrel{~}{\chi }}_{1,2}^{0}$ are the two lightest neutralinos. The decay of the a boson into a pair of b-quarks results in a peak in the dijet invariant mass distribution. The final-state signature consists of two leptons, two or more jets, at least one of which is identified as originating from a b-quark, and missing transverse momentum. Observations are consistent with Standard Model expectations and upper limits are set on the product of cross section times branching ratio for a three-dimensional scan of the masses of the ${\stackrel{~}{\chi }}_{2}^{0}$ , ${\stackrel{~}{\chi }}_{1}^{0}$ and a boson.