A search for dark matter particles produced in association with a Higgs boson
decaying into a pair of τ leptons is performed using data collected in proton-proton collisions at
a center-of-mass energy of 13TeV with the CMS detector. The analysis is based on a data set
corresponding to an integrated luminosity of 101fb−1 collected in 2017–2018. No significant
excess over the expected standard model background is observed. This result is interpreted
within the frameworks of the 2HDM+a and baryonic Z′ benchmark simplified models. The
2HDM+a model is a type-II two-Higgs-doublet model featuring a heavy pseudoscalar with
an additional light pseudoscalar. Upper limits at 95% confidence level are set on the product
of the production cross section and the branching fraction for each of these two simplified
models. Heavy pseudoscalar boson masses between 400 and 700GeV are excluded for a light
pseudoscalar mass of 100GeV. For the baryonic Z′ model, a statistical combination is made
with an earlier search based on a data set of 36fb−1 collected in 2016. In this model, Z′ boson
masses up to 1050GeV are excluded for a dark matter particle mass of 1GeV.
