Search for heavy resonances decaying into two Higgs bosons in the $$\text {b}{\bar{\text {b}}} \tau ^{+} \tau ^{-} $$ final state in proton–proton collisions at $$\sqrt{s} = 13\,\text {Te}\hspace{-.08em}\text {V} $$

Abstract A search is presented for massive narrow-width resonances in the mass range of 1–4.5 $$\,\text {Te}\hspace{-.08em}\text {V}$$ Te V , decaying into pairs of Higgs bosons (HH). The search uses proton–proton collision data at a center-of-mass energy of 13 $$\,\text {Te}\hspace{-.08em}\text {V}$$ Te V collected with the CMS detector at the CERN LHC during 2016–2018, corresponding to an integrated luminosity of 138 $$\,\text {fb}^{-1}$$ fb - 1 . The analysis targets final states where one Higgs boson decays into a pair of bottom quarks and the other into a pair of tau leptons, $${\text {X}} \rightarrow {\text {HH}} \rightarrow \text {b}{\bar{\text {b}}}\,\tau ^{+}\tau ^{-} $$ X → HH → b b ¯ τ + τ - . It uses a single large radius jet to reconstruct the $${\text {H}} \rightarrow \text {b}{\bar{\text {b}}}$$ H → b b ¯ decay, while the $${\text {H}} \rightarrow \tau ^{+}\tau ^{-} $$ H → τ + τ - decay products can either be contained within a single large radius jet or appear as two isolated tau leptons. The observed data are consistent with standard model background expectations. Upper limits at 95% confidence level are set on the production cross section for resonant HH production for masses between 1 and 4.5 $$\,\text {Te}\hspace{-.08em}\text {V}$$ Te V . This analysis sets the most sensitive limits to date on $${\text {X}} \rightarrow {\text {HH}} \rightarrow \text {b}\bar{\hbox {b}}\, \tau ^{+}\tau ^{-} $$ X → HH → b b ¯ τ + τ - decays in the mass range of 1.4–4.5 $$\,\text {Te}\hspace{-.08em}\text {V}$$ Te V