Abstract
A search for a heavy, CP-odd Higgs boson, A, decaying into a Z boson and a 125 GeV Higgs boson, h, with the ATLAS detector at the LHC is presented. The search uses proton–proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb−1. Decays of CP-even h bosons to ττ or bb pairs with the Z boson decaying to electron or muon pairs are considered, as well as h→bb decays with the Z boson decaying to neutrinos. No evidence for the production of an A boson in these channels is found and the 95% confidence level upper limits derived for σ(gg→A)×BR(A→Zh)×BR(h→ff¯) are 0.098–0.013 pb for f=τ and 0.57–0.014 pb for f=b in a range of mA=220–1000 GeV. The results are combined and interpreted in the context of two-Higgs-doublet models.
Highlights
After the discovery of a Higgs boson at the LHC in 2012 [1,2], one of the most important remaining questions is whether the newly discovered particle is part of an extended scalar sector
The addition of a second Higgs doublet leads to five Higgs bosons after the electroweak symmetry breaking
The exclusion limits are calculated with a modified frequentist method [48], known as confidence level (CL), and the profile likelihood method, Fig. 2
Summary
After the discovery of a Higgs boson at the LHC in 2012 [1,2], one of the most important remaining questions is whether the newly discovered particle is part of an extended scalar sector. A CP-odd Higgs boson, A, appears in many models with an extended scalar sector, e.g. in the case of the two-Higgs-doublet model (2HDM) [3]. The addition of a second Higgs doublet leads to five Higgs bosons after the electroweak symmetry breaking. The A → Zh decay rate can be dominant for part of the 2HDM parameter space, especially for an A boson mass, mA , below the ttthreshold. In this case, the A boson is produced mainly via gluon fusion and its natural width is typically small: A /mA O(1%). The reconstructed invariant mass (or transverse mass) of the Zh pair, employing the measured value of the h boson mass, mh, to improve its resolution, is used to search for a signal
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