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 “${{\mathit H}}$'', can be interpreted as one of the neutral Higgs bosons of an extended Higgs sector.

Mass Limits in General two-Higgs-doublet Models

INSPIRE   PDGID:
S055H2D
VALUE (GeV) CL% DOCUMENT ID TECN  COMMENT
• • We do not use the following data for averages, fits, limits, etc. • •
1
AAD
2023AD
 ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$, ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit H}}{{\mathit H}}$
2
AAD
2023BG
 ATLS ${{\mathit t}}{{\overline{\mathit t}}}{{\mathit H}_{{{2}}}^{0}}/{{\mathit A}^{0}}$
3
AAD
2023O
 ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}}$
4
AAD
2021AF
 ATLS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit Z}}$
5
AAD
2021AI
 ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$
6
AAD
2020
ATLS ${{\mathit H}^{0}}$ properties
7
AAD
2020L
 ATLS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$
8
SIRUNYAN
2020AA
 CMS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$ or ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$
9
SIRUNYAN
2020Y
 CMS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit W}^{+}}{{\mathit W}^{-}}$
10
SIRUNYAN
2019AE
 CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$
11
SIRUNYAN
2019AV
 CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
12
AABOUD
2018AH
 ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$
13
AABOUD
2018AI
 ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
14
AABOUD
2018BF
 ATLS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit Z}}$
15
AABOUD
2018CE
 ATLS ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit H}_{{{2}}}^{0}}$ $/$ ${{\mathit A}^{0}}{{\mathit t}}{{\overline{\mathit t}}}$, ${{\mathit H}_{{{2}}}^{0}}$ $/$ ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit t}}{{\overline{\mathit t}}}$
16
HALLER
2018
RVUE global fits
17
SIRUNYAN
2018BP
 CMS ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit H}_{{{2}}}^{0}}$ $/$ ${{\mathit A}^{0}}{+}$ ${{\mathit b}}{+}$ ${{\mathit X}}$, ${{\mathit H}_{{{2}}}^{0}}$ $/$ ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$
18
SIRUNYAN
2018ED
 CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
19
AABOUD
2017AN
 ATLS ${{\mathit H}_{{{2}}}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit t}}{{\overline{\mathit t}}}$
20
SIRUNYAN
2017AX
 CMS ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
21
AAD
2016AX
 ATLS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit Z}}$
22
KHACHATRYAN
2016P
 CMS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit H}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
23
KHACHATRYAN
2016W
 CMS ${{\mathit A}^{0}}{{\mathit b}}{{\overline{\mathit b}}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$
24
KHACHATRYAN
2016Z
 CMS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$ or ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$
25
AAD
2015BK
 ATLS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit H}^{0}}$
26
AAD
2015S
 ATLS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
27
KHACHATRYAN
2015BB
 CMS ${{\mathit H}_{{{2}}}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$
28
KHACHATRYAN
2015N
 CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
29
AAD
2014M
 ATLS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit H}^{\pm}}{{\mathit W}^{\mp}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit W}^{\pm}}{{\mathit W}^{\mp}}$, ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$
30
KHACHATRYAN
2014Q
 CMS ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit H}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}^{0}}$
31
AALTONEN
2009AR
 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 32
ABBIENDI
2005A
 OPAL ${{\mathit H}_{{{1}}}^{0}}$, Type II model
$> 110.6$ 95 33
ABDALLAH
2005D
 DLPH ${{\mathit H}^{0}}$ $\rightarrow$ 2 jets
34
ABDALLAH
2004O
 DLPH ${{\mathit Z}}$ $\rightarrow$ ${{\mathit f}}{{\overline{\mathit f}}}{{\mathit H}}$
35
ABDALLAH
2004O
 DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit Z}}$, ${{\mathit H}^{0}}{{\mathit A}^{0}}$
36
ABBIENDI
2002D
 OPAL ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit H}}$
$\text{none 1 - 44}$ 95 37
ABBIENDI
2001E
 OPAL ${{\mathit H}_{{{1}}}^{0}}$, Type-II model
$>68.0$ 95 38
ABBIENDI
1999E
 OPAL tan $\beta >1$
39
ABREU
1995H
 DLPH ${{\mathit Z}}$ $\rightarrow$ ${{\mathit H}^{0}}{{\mathit Z}^{*}}$, ${{\mathit H}^{0}}{{\mathit A}^{0}}$
40
PICH
1992
RVUE Very light Higgs
1  AAD 2023AD search for associated production of ${{\mathit W}}/{{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$ and gluon fusion production of ${{\mathit A}^{0}}$ decaying to ${{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$, with the decay chain ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit H}}{{\mathit H}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}{{\mathit b}}{{\overline{\mathit b}}}$, using 139 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 12 and 13 for excluded regions in Type-I and lepton-specific 2HDMs.
2  AAD 2023BG search for production of ${{\mathit H}_{{{2}}}^{0}}/{{\mathit A}^{0}}$ in association with a ${{\mathit t}}{{\overline{\mathit t}}}$ pair, decaying to ${{\mathit t}}{{\overline{\mathit t}}}$, using 139 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 8 for excluded regions in the parameter space of the type II 2HDM.
3  AAD 2023O search for production of an ${{\mathit A}^{0}}$ in gluon-gluon fusion and in association with a ${{\mathit b}}{{\overline{\mathit b}}}$, decaying to ${{\mathit Z}}{{\mathit H}}$ in the final states ${{\mathit \nu}}{{\overline{\mathit \nu}}}{{\mathit b}}{{\overline{\mathit b}}}$ and ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ using 139 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 12 and 13 for excluded regions in the parameter space in various 2HDMs.
4  AAD 2021AF 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 139 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 6 and 7 for excluded parameter regions of the 2HDM Type I and II.
5  AAD 2021AI search for production of an ${{\mathit A}^{0}}$ in gluon-gluon fusion and in association with a ${{\mathit b}}{{\overline{\mathit b}}}$, decaying to ${{\mathit Z}}$ ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ or ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit W}^{+}}{{\mathit W}^{-}}$ in 139 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 10 and 14 for excluded regions in the parameter space of various 2HDMs.
6  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.
7  AAD 2020L search for ${{\mathit b}}$-associated production of ${{\mathit H}_{{{2}}}^{0}}$ decaying to ${{\mathit b}}{{\overline{\mathit b}}}$ in 27.8 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 10 and 11 for excluded regions in the flipped two Higgs doublet model.
8  SIRUNYAN 2020AA search for ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$ or ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit H}_{{{2}}}^{0}}$, ${{\mathit H}_{{{2}}}^{0}}$ $\rightarrow$ ${{\mathit b}}{{\overline{\mathit b}}}$ in 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Figs. 8 and 9 for excluded regions in the parameter space of Type-II two Higgs doublet model.
9  SIRUNYAN 2020Y search for gluon-fusion and vector-boson-fusion production of ${{\mathit H}_{{{2}}}^{0}}$ decaying to ${{\mathit W}^{+}}{{\mathit W}^{-}}$ in the final states ${{\mathit \ell}}{{\mathit \nu}}{{\mathit \ell}}{{\mathit \nu}}$ and ${{\mathit \ell}}{{\mathit \nu}}{{\mathit q}}{{\mathit q}}$ in 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 7 for excluded regions in Type I and II two Higgs doublet models.
10  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.
11  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.
12  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.
13  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.
14  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.
15  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.
16  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.
17  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.
18  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.
19  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.
20  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( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$).
21  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.
22  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.
23  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( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$).
24  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.
25  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.
26  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.
27  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.
28  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.
29  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.
30  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.
31  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.
32  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 ${{\mathit H}_{{{1}}}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$.
33  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.
34  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.
35  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.
36  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.
37  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.
38  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.
39  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.
40  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