Z-Boson Control Region and Search for a Heavy Higgs Boson in $H \to WW \to \ell v \ell v$ Decay Channel in Proton—Proton Collisions at 13 TeV with the ATLAS Experiment at LHC

The control region of Z-bosons produced in pp collisions at 13 TeV with the ATLAS detector at LHC is studied. This investigation, carried out by the authors as members of the HWW working group, is aimed at checking the algorithms applied for reconstructing the H → WW → ℓvℓv decays of a hypothetical heavy Higgs boson (HHB) sought by the LHC experiments. The analysis relies on the complete sample of proton-proton collisions recorded by ATLAS in 2015–2016 and pays special attention to variations of hadron-jet kinematic characteristics with the collider luminosity. A dedicated software package within the HWW information medium is developed and implemented for plotting kinematic distributions for correlated jets as functions of the number of collisions per beam crossing and of the number of primary vertices per event. On the whole, mean values of kinematic characteristics are found to follow linear dependences on the luminosity which are adequately reproduced by the simulation. Since the hadron-jet selection criteria are similar for the hypothetical HHB and for the Standard Model Higgs boson (SM H) already discovered at the LHC, the reported analysis is also relevant for experimental studies of the SM H properties. In this paper, we also report on initial results of the new search for the HHB at 13 TeV based on ameliorated event reconstruction algorithms and updated software. No significant differences between the results of the new and previous analyses are revealed.