Search for heavy resonances decaying into two Higgs bosons or into a Higgs and a vector boson in proton-proton collisions at 13 TeV

A search is presented for massive resonances decaying either into two Higgs (H) bosons or into a Higgs and a vector (V = W or Z) boson. The decay channels considered are $\mathrm{VH} \rightarrow q\bar{q}\tau^{+}\tau^{-}$ and $\mathrm{HH} \rightarrow b\bar{b}\tau^{+}\tau^{-}$. This analysis is based on the data sample of proton-proton collisions collected at a center-of-mass energy of $13~\mathrm{TeV}$ by the CMS Collaboration in $2016$, corresponding to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$. For the high-mass resonances considered ($\gtrsim 1~\mathrm{TeV}$), substructure techniques are employed to differentiate between the hadronization products of a vector boson decaying to quarks, a Higgs boson decaying to bottom quarks, and quark- or gluon-induced jets. Due to the large boost of the Higgs boson, the two leptons in the $H \rightarrow \tau^{+}\tau^{-}$ decay are collimated. Advanced techniques are used for events in which one $\tau$ lepton decays hadronically and the other leptonically, and in which both decay hadronically. Upper limits at $95\%$ confidence level are set on the product of cross section times branching fraction for resonance masses between $900$ and $4000~\mathrm{GeV}$, ranging from $100$ to $6~\mathrm{fb}$ for spin $0$ and $2$ resonances, and from $250$ to $6~\mathrm{fb}$ for spin $1$ resonances.