Search for non-resonant di-Higgs production in bb + 𝜏𝜏 final states in pp collisions at CMS

A search for non-resonant Higgs-boson pair production (HH) in the bb𝜏𝜏final state is presented at √𝑠 = 13 TeV using the 2018 CMS proton–proton dataset corresponding to 59.8 fb⁻¹ after a common re-optimization of the reconstruction and calibration of the data by the CMS Collaboration. The resolved topology is targeted and three 𝜏⁺𝜏⁻ final states 𝜏_h𝜏_h, 𝜇𝜏_h and e𝜏_h are taken into account, where 𝜏_h refers to the decay of the 𝜏 lepton into hadrons. Object reconstruction and identification are based on Particle Flow, DeepJet and DeepTau v2.5 algorithms. A multi-class classification neural network is used for event discrimination and category definition. The background from QCD multijet events is estimated from data via an ABCD method using the charges and DeepTau vsJet discriminants to define corresponding control regions. The di-𝜏 invariant mass, a key observable for discriminating signal from background, is reconstructed using the FastMTT algorithm. 

Expected upper limits are derived from a profile-likelihood fit to the Asimov dataset. The median expected 95 % CL upper limit on the signal strength 𝜇= 𝜎_{(pp →HH)}/𝜎_SM is found to be 𝜇_exp⁹⁵ = 10.9, about 2 % weaker than the result obtained when considering only statistical uncertainties (𝜇_exp⁹⁵ = 10.7). Projections obtained from scaling rates with integrated luminosity while keeping shapes and the size of nominal systematics yield median expected 95 % CL limits of 𝜇_exp⁹⁵ = 7.2 for the full Run 2 corresponding to an integrated luminosity of 138 fb⁻¹ and 𝜇_exp⁹⁵ = 4.7 for a Run 2 + Run 3 scenario with 500 fb⁻¹.