# MASS LIMITS FOR NEUTRAL HIGGS BOSONS IN EXTENDED HIGGS MODELS

This Section covers models which do not fit into either the Standard Model or its simplest minimal Supersymmetric extension (MSSM), leading to anomalous production rates, or nonstandard final states and branching ratios. In particular, this Section covers limits which may apply to generic two-Higgs-doublet models (2HDM), or to special regions of the MSSM parameter space where decays to invisible particles or to photon pairs are dominant (see the review on Status of Higgs Boson Physics''). Concerning the mass limits for ${{\mathit H}^{0}}$ and ${{\mathit A}^{0}}$ listed below, see the footnotes or the comment lines for details on the nature of the models to which the limits apply.
The observed signal at about 125 GeV, see section ${{\mathit H}^{0}}$'', can be interpreted as one of the neutral Higgs bosons of an extended Higgs sector.

# Mass Limits in General two-Higgs-doublet Models INSPIRE search

VALUE (GeV) CL% DOCUMENT ID TECN  COMMENT
• • • We do not use the following data for averages, fits, limits, etc. • • •
1
 2020
ATLS ${{\mathit H}^{0}}$ properties
2
 2019 AE
CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$
3
 2019 AV
CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
4
 2018 AH
ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{2}}^{0}}$
5
 2018 AI
ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
6
 2018 BF
ATLS ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit Z}}$
7
 2018 CE
ATLS ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit H}_{{2}}^{0}}$ $/$ ${{\mathit A}^{0}}{{\mathit t}}{{\overline{\mathit t}}}$ , ${{\mathit H}_{{2}}^{0}}$ $/$ ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit t}}{{\overline{\mathit t}}}$
8
 2018
RVUE global fits
9
 2018 BP
CMS ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit H}_{{2}}^{0}}$ $/$ ${{\mathit A}^{0}}{+}$ ${{\mathit b}}{+}$ ${{\mathit X}}$ , ${{\mathit H}_{{2}}^{0}}$ $/$ ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$
10
 2018 ED
CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
11
 2017 AN
ATLS ${{\mathit H}_{{2}}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit t}}{{\overline{\mathit t}}}$
12
 2017 AX
CMS ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
13
 2016 AX
ATLS ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit Z}}$
14
 2016 P
CMS ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit H}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
15
 2016 W
CMS ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$
16
 2016 Z
CMS ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$ or ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{2}}^{0}}$
17
 2015 BK
ATLS ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit H}^{0}}$
18
 2015 S
ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
19
 2015 BB
CMS ${{\mathit H}_{{2}}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$
20
 2015 N
CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
21
 2014 M
ATLS ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit H}^{\pm}}{{\mathit W}^{\mp}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit W}^{\pm}}{{\mathit W}^{\mp}}$ , ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$
22
 2014 Q
CMS ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit H}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
23
 2009 AR
CDF ${{\mathit p}}$ ${{\overline{\mathit p}}}$ $\rightarrow$ ${{\mathit H}^{0}_{{{1,2}}}}$ $/$ ${{\mathit A}^{0}}{+}$ ${{\mathit X}}$ , ${{\mathit H}^{0}_{{{1,2}}}}$ $/$ ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$
$\text{none 1 - 55}$ 95 24
 2005 A
OPAL ${{\mathit H}_{{1}}^{0}}$, Type II model
$> 110.6$ 95 25
 2005 D
DLPH ${{\mathit H}^{0}}$ $\rightarrow$ 2 jets
26
 2004 O
DLPH ${{\mathit Z}}$ $\rightarrow$ ${{\mathit f}}{{\overline{\mathit f}}}{{\mathit H}}$
27
 2004 O
DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit Z}}$ , ${{\mathit H}^{0}}{{\mathit A}^{0}}$
28
 2002 D
OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit H}}$
$\text{none 1 - 44}$ 95 29
 2001 E
OPAL ${{\mathit H}_{{1}}^{0}}$, Type-II model
$>68.0$ 95 30
 1999 E
OPAL tan $\beta >1$
31
 1995 H
DLPH ${{\mathit Z}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit Z}^{*}}$ , ${{\mathit H}^{0}}{{\mathit A}^{0}}$
32
 1992
RVUE Very light Higgs
1  AAD 2020 combine measurements on ${{\mathit H}^{0}}$ production and decay using data taken in years $2015 - 2017$ (up to 79.8 fb${}^{-1}$) of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 18 for excluded regions in various 2HDMs.
2  SIRUNYAN 2019AE search for a pseudoscalar resonance produced in association with a ${{\mathit b}}{{\overline{\mathit b}}}$ pair, decaying to ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ in 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 4 for cross section limits for ${\mathit m}_{{{\mathit A}^{0}}}$ = $25 - 70$ GeV and comparison with some representative 2HDMs.
3  SIRUNYAN 2019AV search for a scalar resonance produced by gluon fusion or ${{\mathit b}}$ associated production, decaying to ${{\mathit Z}}$ ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ (${{\mathit \ell}}$ = ${{\mathit e}}$, ${{\mathit \mu}}$) or ${{\mathit \nu}}{{\overline{\mathit \nu}}}{{\mathit b}}{{\overline{\mathit b}}}$ in 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 6 and 7 for excluded regions in the parameter space of various 2HDMs.
4  AABOUD 2018AH search for production of an ${{\mathit A}^{0}}$ in gluon-gluon fusion and in association with a ${{\mathit b}}{{\overline{\mathit b}}}$ , decaying to ${{\mathit Z}}$ ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ in 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 6 for excluded regions in the parameter space of various 2HDMs.
5  AABOUD 2018AI search for production of an ${{\mathit A}^{0}}$ in gluon-gluon fusion and in association with a ${{\mathit b}}{{\overline{\mathit b}}}$ , decaying to ${{\mathit Z}}{{\mathit H}^{0}}$ in the final states ${{\mathit \nu}}{{\overline{\mathit \nu}}}{{\mathit b}}{{\overline{\mathit b}}}$ and ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ in 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 7 and 8 for excluded regions in the parameter space in various 2HDMs.
6  AABOUD 2018BF search for production of a heavy ${{\mathit H}_{{2}}^{0}}$ state decaying to ${{\mathit Z}}{{\mathit Z}}$ in the final states ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ and ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ in 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 8 and 9 for excluded parameter regions in 2HDM Type I and II.
7  AABOUD 2018CE search for the process ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit H}_{{2}}^{0}}$ $/$ ${{\mathit A}^{0}}{{\mathit t}}{{\overline{\mathit t}}}$ followed by the decay ${{\mathit H}_{{2}}^{0}}$ $/$ ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit t}}{{\overline{\mathit t}}}$ in 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 12 for limits on cross section times branching ratio, and for lower limits on tan $\beta$ for ${\mathit m}_{{{\mathit H}_{{2}}^{0}}}$, ${\mathit m}_{{{\mathit A}^{0}}}$ = $0.4 - 1.0$ TeV in the 2HDM type II.
8  HALLER 2018 perform global fits in the framework of two-Higgs-doublet models (type I, II, lepton specific, flipped). See their Fig. 8 for allowed parameter regions from fits to LHC ${{\mathit H}^{0}}$ measurements, Fig. 9 bottom and charm decays, Fig. 10 muon anomalous magnetic moment, Fig. 11 electroweak precision data, and Fig. 12 by combination of all data.
9  SIRUNYAN 2018BP search for production of ${{\mathit H}_{{2}}^{0}}$ $/$ ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$ by ${{\mathit b}}$-associated prodution in 35.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 6 for the limits on cross section times branching ratio for ${\mathit m}_{{{\mathit H}_{{2}}^{0}}}$, ${\mathit m}_{{{\mathit A}^{0}}}$ = $0.3 - 1.3$ TeV, and Figs. 8 and 9 for excluded regions in the parameter space of type-II and flipped 2HDMs.
10  SIRUNYAN 2018ED search for production of an ${{\mathit A}^{0}}$ in gluon-gluon fusion and in association with a ${{\mathit b}}{{\overline{\mathit b}}}$ , decaying to ${{\mathit Z}}{{\mathit H}^{0}}$ in the final states ${{\mathit \nu}}{{\overline{\mathit \nu}}}{{\mathit b}}{{\overline{\mathit b}}}$ or ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ in 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 9 for excluded regions in the parameter space in Type I and II 2HDMs.
11  AABOUD 2017AN search for production of a heavy ${{\mathit H}_{{2}}^{0}}$ and/or ${{\mathit A}^{0}}$ decaying to ${{\mathit t}}{{\overline{\mathit t}}}$ in 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Fig. 3 and Table III for excluded parameter regions in Type II Two-Higgs-Doublet-Models.
12  SIRUNYAN 2017AX search for ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}$ production followed by the decay ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ in 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. Limits are set in the range ${\mathit m}_{{{\mathit A}^{0}}}$ = $25 - 60$ GeV. See their Fig. 5 for upper limits on ${\mathit \sigma (}$ ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}{)}\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ).
13  AAD 2016AX search for production of a heavy ${{\mathit H}^{0}}$ state decaying to ${{\mathit Z}}{{\mathit Z}}$ in the final states ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ , ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ , ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit q}}{{\overline{\mathit q}}}$ , and ${{\mathit \nu}}{{\overline{\mathit \nu}}}{{\mathit q}}{{\overline{\mathit q}}}$ in 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Figs. 13 and 14 for excluded parameter regions in Type I and II models.
14  KHACHATRYAN 2016P search for gluon fusion production of an ${{\mathit H}_{{2}}^{0}}$ decaying to ${{\mathit H}^{0}}$ ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ and an ${{\mathit A}^{0}}$ decaying to ${{\mathit Z}}$ ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ in 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Fig. 11 for limits on tan $\beta$ for ${\mathit m}_{{{\mathit A}^{0}}}$ = $230 - 350$ GeV.
15  KHACHATRYAN 2016W search for ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}$ production followed by the decay ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ in 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Fig. 3 for upper limits on $\sigma$( ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ ).
16  KHACHATRYAN 2016Z search for ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$ followed by ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$ or ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ , and ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{2}}^{0}}$ followed by ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$ or ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ , in 19.8 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Fig. 4 for cross section limits and Fig. 5 for excluded region in the parameter space.
17  AAD 2015BK search for production of a heavy ${{\mathit H}_{{2}}^{0}}$ decaying to ${{\mathit H}^{0}}{{\mathit H}^{0}}$ in the final state ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit b}}{{\overline{\mathit b}}}$ in 19.5 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Figs. $15 - 18$ for excluded regions in the parameter space.
18  AAD 2015S search for production of ${{\mathit A}^{0}}$ decaying to ${{\mathit Z}}$ ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ , ${{\mathit \nu}}{{\overline{\mathit \nu}}}{{\mathit b}}{{\overline{\mathit b}}}$ and ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ in 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Figs. 4 and 5 for excluded regions in the parameter space.
19  KHACHATRYAN 2015BB search for ${{\mathit H}_{{2}}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ in 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Fig. 10 for excluded regions in the two-Higgs-doublet model parameter space.
20  KHACHATRYAN 2015N search for production of ${{\mathit A}^{0}}$ decaying to ${{\mathit Z}}$ ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ in 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Fig. 5 for excluded regions in the tan $\beta$ $−$ cos $(\beta −\alpha )$ plane for ${\mathit m}_{{{\mathit A}^{0}}}$ = 300 GeV.
21  AAD 2014M search for the decay cascade ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit H}^{\pm}}{{\mathit W}^{\mp}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit W}^{\pm}}{{\mathit W}^{\mp}}$ , ${{\mathit H}^{0}}$ decaying to ${{\mathit b}}{{\overline{\mathit b}}}$ in 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Table IV for limits in a two-Higgs-doublet model for ${\mathit m}_{{{\mathit H}_{{2}}^{0}}}$= $325 - 1025$ GeV and ${\mathit m}_{{{\mathit H}^{+}}}$= $225 - 825$ GeV.
22  KHACHATRYAN 2014Q search for ${{\mathit H}_{{2}}^{0}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit H}^{0}}$ and ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$ in 19.5 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Figs. 4 and 5 for limits on cross section times branching ratio for ${{\mathit m}}_{{{\mathit H}_{{2}}},{{\mathit A}^{0}}}$= $260 - 360$ GeV and their Figs. $7 - 9$ for limits in two-Higgs-doublet models.
23  AALTONEN 2009AR search for Higgs bosons decaying to ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ in two doublet models in 1.8 fb${}^{-1}$ of ${{\mathit p}}{{\overline{\mathit p}}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 1.96 TeV. See their Fig. 2 for the limit on $\sigma \cdot{}$B( ${{\mathit H}^{0}_{{{1,2}}}}$ / ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ ) for different Higgs masses, and see their Fig. 3 for the excluded region in the MSSM parameter space.
24  ABBIENDI 2005A search for ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit H}_{{1}}^{0}}{{\mathit A}^{0}}$ in general Type-II two-doublet models, with decays ${{\mathit H}_{{1}}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit q}}{{\overline{\mathit q}}}$ , ${{\mathit g}}{{\mathit g}}$ , ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ , and ${{\mathit H}_{{1}}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ .
25  ABDALLAH 2005D search for ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit Z}}$ and ${{\mathit H}^{0}}{{\mathit A}^{0}}$ with ${{\mathit H}^{0}}$, ${{\mathit A}^{0}}$ decaying to two jets of any flavor including ${{\mathit g}}{{\mathit g}}$ . The limit is for SM ${{\mathit H}^{0}}{{\mathit Z}}$ production cross section with B( ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit j}}{{\mathit j}}$ ) = 1.
26  ABDALLAH 2004O search for ${{\mathit Z}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit H}^{0}}$ , ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit A}^{0}}$ , ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}{{\mathit H}^{0}}$ and ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}{{\mathit A}^{0}}$ in the final states 4 ${{\mathit b}}$ , ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ , and 4 ${{\mathit \tau}}$ . See paper for limits on Yukawa couplings.
27  ABDALLAH 2004O search for ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit Z}}$ and ${{\mathit H}^{0}}{{\mathit A}^{0}}$ , with ${{\mathit H}^{0}}$, ${{\mathit A}^{0}}$ decaying to ${{\mathit b}}{{\overline{\mathit b}}}$ , ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ , or ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ at $\mathit E_{{\mathrm {cm}}}$ = $189 - 208$ GeV. See paper for limits on couplings.
28  ABBIENDI 2002D search for ${{\mathit Z}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit H}_{{1}}^{0}}$ and ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit A}^{0}}$ with ${{\mathit H}_{{1}}^{0}}$ /${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ , in the range 4$<{\mathit m}_{{{\mathit H}}}<$12 GeV. See their Fig.$~$8 for limits on the Yukawa coupling.
29  ABBIENDI 2001E search for neutral Higgs bosons in general Type-II two-doublet models, at $\mathit E_{{\mathrm {cm}}}{}\leq{}$189 GeV. In addition to usual final states, the decays ${{\mathit H}_{{1}}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit q}}{{\overline{\mathit q}}}$ , ${{\mathit g}}{{\mathit g}}$ are searched for. See their Figs.$~$15,16 for excluded regions.
30  ABBIENDI 1999E search for ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit A}^{0}}$ and ${{\mathit H}^{0}}{{\mathit Z}}$ at $\mathit E_{{\mathrm {cm}}}$ = 183 GeV. The limit is with ${\mathit m}_{{{\mathit H}}}={\mathit m}_{{{\mathit A}}}$ in general two Higgs-doublet models. See their Fig.$~$18 for the exclusion limit in the ${\mathit m}_{{{\mathit H}}}-{\mathit m}_{{{\mathit A}}}$ plane. Updates the results of ACKERSTAFF 1998S.
31  See Fig.$~$4 of ABREU 1995H for the excluded region in the ${\mathit m}_{{{\mathit H}^{0}}}–{\mathit m}_{{{\mathit A}^{0}}}$ plane for general two-doublet models. For tan $\beta >$1, the region ${\mathit m}_{{{\mathit H}^{0}}}+{\mathit m}_{{{\mathit A}^{0}}}{ {}\lesssim{} }$87 GeV, ${\mathit m}_{{{\mathit H}^{0}}}<$47 GeV is excluded at 95$\%$ CL.
32  PICH 1992 analyse ${{\mathit H}^{0}}$ with ${\mathit m}_{{{\mathit H}^{0}}}<$ 2${\mathit m}_{{{\mathit \mu}}}$ in general two-doublet models. Excluded regions in the space of mass-mixing angles from LEP, beam dump, and ${{\mathit \pi}^{\pm}}$, ${{\mathit \eta}}$ rare decays are shown in Figs.$~$3,4. The considered mass region is not totally excluded.
References:
PR D101 012002 Combined measurements of Higgs boson production and decay using up to $80$ fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=$ 13 TeV collected with the ATLAS experiment
 SIRUNYAN 2019AV
EPJ C79 564 Search for a heavy pseudoscalar boson decaying to a Z and a Higgs boson at $\sqrt{s} =$ 13 TeV
 SIRUNYAN 2019AE
JHEP 1905 210 Search for a low-mass $\tau^+\tau^-$ resonance in association with a bottom quark in proton-proton collisions at $\sqrt{s}=$ 13 TeV
 AABOUD 2018AH
PL B783 392 Search for a heavy Higgs boson decaying into a $Z$ boson and another heavy Higgs boson in the $\ell\ell bb$ final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
 AABOUD 2018CE
JHEP 1812 039 Search for new phenomena in events with same-charge leptons and $b$-jets in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector
 AABOUD 2018AI
JHEP 1803 174 Search for heavy resonances decaying into a $W$ or $Z$ boson and a Higgs boson in final states with leptons and $b$-jets in 36 fb$^{-1}$ of $\sqrt s = 13$ TeV $pp$ collisions with the ATLAS detector
 AABOUD 2018BF
EPJ C78 293 Search for heavy ZZ resonances in the $\ell ^+\ell ^-\ell ^+\ell ^-$ and $\ell ^+\ell ^-\nu \bar{\nu }$ final states using proton?proton collisions at $\sqrt{s}= 13$   $\text {TeV}$ with the ATLAS detector
 HALLER 2018
EPJ C78 675 Update of the global electroweak fit and constraints on two-Higgs-doublet models
 SIRUNYAN 2018BP
JHEP 1808 113 Search for beyond the standard model Higgs bosons decaying into a $\mathrm{b\overline{b}}$ pair in pp collisions at $\sqrt{s} =$ 13 TeV
 SIRUNYAN 2018ED
JHEP 1811 172 Search for heavy resonances decaying into a vector boson and a Higgs boson in final states with charged leptons, neutrinos and b quarks at $\sqrt{s}=13$ TeV
 AABOUD 2017AN
PRL 119 191803 Search for Heavy Higgs Bosons ${{\mathit A}}/{{\mathit H}}$ Decaying to a Top Quark Pair in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV with the ATLAS Detector
 SIRUNYAN 2017AX
JHEP 1711 010 Search for a Light Pseudoscalar Higgs Boson Produced in Association with Bottom Quarks in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV
EPJ C76 45 Search for an Additional, Heavy Higgs Boson in the ${{\mathit H}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit Z}}$ Decay Channel at $\sqrt {s }$ = 8 TeV in ${{\mathit p}}{{\mathit p}}$ Collision Data with the ATLAS Detector
 KHACHATRYAN 2016P
PL B755 217 Searches for a Heavy Scalar Boson ${{\mathit H}}$ Decaying to a Pair of 125 GeV Higgs Bosons ${{\mathit h}}{{\mathit h}}$ or for a Heavy Pseudoscalar Boson ${{\mathit A}}$ Decaying to ${{\mathit Z}}{{\mathit h}}$, in the Final States with ${{\mathit h}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \tau}}$
 KHACHATRYAN 2016W
PL B758 296 Search for a Low-Mass Pseudoscalar Higgs Boson Produced in Association with a ${\mathit {\mathit b}}{\mathit {\overline{\mathit b}}}$ Pair in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV
 KHACHATRYAN 2016Z
PL B759 369 Search for Neutral Resonances Decaying into a ${{\mathit Z}}$ Boson and a Pair of ${\mathit {\mathit b}}$ Jets or tau Leptons
PL B744 163 Search for a $\mathit CP$-odd Higgs Boson Decaying to $\mathit Zh$ in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV with the ATLAS Detector
EPJ C75 412 Search for Higgs Boson Pair Production in the ${\mathit {\mathit b}}{\mathit {\overline{\mathit b}}}{\mathit {\mathit b}}{\mathit {\overline{\mathit b}}}$ Final State from ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV with the ATLAS Detector
 KHACHATRYAN 2015N
PL B748 221 Search for a Pseudoscalar Boson Decaying into a ${{\mathit Z}}$ Boson and the 125 GeV Higgs Boson in ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{\mathit {\mathit b}}{\mathit {\overline{\mathit b}}}$ Final States
 KHACHATRYAN 2015BB
PL B750 494 Search for Diphoton Resonances in the Mass Range from 150 to 850 GeV in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV
PR D89 032002 Search for a Multi-Higgs-Boson Cascade in ${{\mathit W}^{+}}{{\mathit W}^{-}}{\mathit {\mathit b}}{\mathit {\overline{\mathit b}}}$ Events with the ATLAS Detector in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV
 KHACHATRYAN 2014Q
PR D90 112013 Searches for Heavy Higgs Bosons in Two-Higgs-Doublet Models and for t $\rightarrow$ ch Decay using Multilepton and Diphoton Final States in ${{\mathit p}}{{\mathit p}}$ Collisions at 8 TeV
 AALTONEN 2009AR
PRL 103 201801 Search for Higgs Bosons Predicted in Two-Higgs-Doublet Models via Decays to Tau Lepton Pairs in 1.96 TeV ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions
 ABBIENDI 2005A
EPJ C40 317 Flavour-Independent $\mathit h{}^{0}\mathit A{}^{0}$ Search and Two Higgs Doublet Model Interpretation of Neutral Higgs Boson Searches at LEP
 ABDALLAH 2005D
EPJ C44 147 Flavour Independent Searches for Hadronically Decaying Neutral Higgs Bosons
 ABDALLAH 2004O
EPJ C38 1 Searches for Neutral Higgs Bosons in Extended Models
 ABBIENDI 2002D
EPJ C23 397 Search for Yukawa Production of a Light Neutral Higgs Boson at LEP
 ABBIENDI 2001E
EPJ C18 425 Two Higgs Doublet Model and Model Independent Interpretation of Neutral Higgs Boson Searches
 ABBIENDI 1999E
EPJ C7 407 Search for Higgs Bosons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions at 183 GeV
 ABREU 1995H
ZPHY C67 69 Search for Heavy Neutral Higgs Bosons in Two Doublet Models
 PICH 1992
NP B388 31 Bounds on a Light Scalar in Two Higgs Doublet Models