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 for Light ${{\mathit A}^{0}}$

INSPIRE   PDGID:
S055H2A
These limits are for a pseudoscalar ${{\mathit A}^{0}}$ in the mass range below $\cal O$(10) GeV.
VALUE (GeV) DOCUMENT ID TECN  COMMENT
• • We do not use the following data for averages, fits, limits, etc. • •
1
ABLIKIM
2022H
 BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
2
JIA
2022
BELL ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
3
AAD
2020AE
 ATLS ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$
4
AABOUD
2018AP
 ATLS ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$
5
KHACHATRYAN
2017AZ
 CMS ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$
6
ABLIKIM
2016E
 BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
7
KHACHATRYAN
2016F
 CMS ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$
8
LEES
2015H
 BABR ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
9
LEES
2013C
 BABR ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
10
LEES
2013L
 BABR ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
11
LEES
2013R
 BABR ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
12
ABLIKIM
2012
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
13
CHATRCHYAN
2012V
 CMS ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
14
AALTONEN
2011P
 CDF ${{\mathit t}}$ $\rightarrow$ ${{\mathit b}}{{\mathit H}^{+}}$ , ${{\mathit H}^{+}}$ $\rightarrow$ ${{\mathit W}^{+}}{{\mathit A}^{0}}$
15, 16
ABOUZAID
2011A
 KTEV ${{\mathit K}_{{L}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
17
DEL-AMO-SANCH..
2011J
 BABR ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
18
LEES
2011H
 BABR ${{\mathit \Upsilon}{(2S,3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
19
ANDREAS
2010
RVUE
20, 16
HYUN
2010
BELL ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit K}^{*0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
21, 16
HYUN
2010
BELL ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit \rho}^{0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
22
AUBERT
2009P
 BABR ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
23
AUBERT
2009Z
 BABR ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
24
AUBERT
2009Z
 BABR ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
25, 16
TUNG
2009
K391 ${{\mathit K}_{{L}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$
26
LOVE
2008
CLEO ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
27
BESSON
2007
CLEO ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit \eta}_{{b}}}{{\mathit \gamma}}$
28
PARK
2005
HYCP ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
29
BALEST
1995
CLE2 ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
30
ANTREASYAN
1990C
 CBAL ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$
1  ABLIKIM 2022H search for the process ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ in $9 \times 10^{9}{{\mathit J / \psi}}$ events and give limits on B( ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range $1.2 \times 10^{-9} - 7.78 \times 10^{-7}$ (90$\%$ CL) for 0.212 GeV ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 3.0 GeV. See their Fig. 4.
2  JIA 2022 search for the process ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit \Upsilon}{(1S)}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ or ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ in $158 \times 10^{6}{{\mathit \Upsilon}{(2S)}}$ events and give limits on B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ ) in the range $3.8 \times 10^{-6} - 1.5 \times 10^{-4}$ (90$\%$ CL) for ${\mathit m}_{{{\mathit A}^{0}}}$ = $3.6 - 9.2$ GeV, and B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range $3.1 \times 10^{-7} - 1.6 \times 10^{-5}$ (90$\%$ CL) for ${\mathit m}_{{{\mathit A}^{0}}}$ = $0.21 - 9.2$ GeV. See their Fig. 4.
3  AAD 2020AE search for the decay ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$ , ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ , ${{\mathit A}^{0}}$ decaying hadronically ( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit g}}{{\mathit g}}$ or ${{\mathit s}}{{\overline{\mathit s}}}$ ), in 139 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. Limit on the product of production cross section and the ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$ branching ratio in the range $17 - 340$ pb (95$\%$ CL) is given for ${\mathit m}_{{{\mathit A}^{0}}}$ = $0.5 - 4.0$ GeV, see their Table I.
4  AABOUD 2018AP search for the decay ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ in 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. See their Fig. 10(b) for limits on B( ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ ) in the range ${\mathit m}_{{{\mathit A}^{0}}}$ = $1 - 2.5$, $4.5 - 8$ GeV, assuming a type-II two-doublet plus singlet model with tan$(\beta )$ = 5.
5  KHACHATRYAN 2017AZ search for the decay ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ , ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit b}}{{\overline{\mathit b}}}$ , and ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ in 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Figs. 4, 5, and 6 for cross section limits in the range ${\mathit m}_{{{\mathit A}^{0}}}$ = $5 - 62.5$ GeV. See also their Figs. 7, 8, and 9 for interpretation of the data in terms of models with two Higgs doublets and a singlet.
6  ABLIKIM 2016E search for the process ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ and give limits on B( ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range $2.8 \times 10^{-8} - 5.0 \times 10^{-6}$ (90$\%$ CL) for 0.212 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 3.0 GeV. See their Fig. 5.
7  KHACHATRYAN 2016F search for the decay ${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ in 19.7 fb${}^{-1}$ of ${{\mathit p}}$ ${{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. See their Fig. 8 for cross section limits for ${\mathit m}_{{{\mathit A}^{0}}}$ = $4 - 8$ GeV.
8  LEES 2015H search for the process ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit \Upsilon}{(1S)}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit c}}{{\overline{\mathit c}}}$ and give limits on B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit c}}{{\overline{\mathit c}}}$ ) in the range $7.4 - 2.4$ (90$\%$ CL) for 4.00 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 8.95 and 9.10 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 9.25 GeV. See their Fig. 6.
9  LEES 2013C search for the process ${{\mathit \Upsilon}}$(2S, 3S) $\rightarrow$ ${{\mathit \Upsilon}{(1S)}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ and give limits on B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range ($0.3 - 9.7){\times }10^{-6}$ (90$\%$ CL) for 0.212 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 9.20 GeV. See their Fig. 5(e) for limits on the ${{\mathit b}}−{{\mathit A}^{0}}$ Yukawa coupling derived by combining this result with AUBERT 2009Z.
10  LEES 2013L search for the process ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit \Upsilon}{(1S)}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit g}}{{\mathit g}}$ or ${{\mathit s}}{{\overline{\mathit s}}}$ and give limits on B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit g}}{{\mathit g}}$ ) between $1 \times 10^{-6}$ and $0.02$ (90$\%$ CL) for 0.5 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 9.0 GeV, and B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit s}}{{\overline{\mathit s}}}$ ) between $4 \times 10^{-6}$ and $1 \times 10^{-3}$ (90$\%$CL) for 1.5 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 9.0 GeV. See their Fig. 4.
11  LEES 2013R search for the process ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit \Upsilon}{(1S)}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ and give limits on B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ ) in the range $0.9 - 13 \times 10^{-5}$ (90$\%$ CL) for 3.6 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 9.2 GeV. See their Fig. 4 for limits on the ${{\mathit b}}−{{\mathit A}^{0}}$ Yukawa coupling derived by combining this result with AUBERT 2009P.
12  ABLIKIM 2012 searches for the process ${{\mathit \psi}{(3686)}}$ $\rightarrow$ ${{\mathit \pi}}{{\mathit \pi}}{{\mathit J / \psi}}$ , ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ decaying to ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ . It gives mass dependent limits on B( ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range $4 \times 10^{-7} - 2.1 \times 10^{-5}$ (90$\%$ C.L.) for 0.212 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 3.0 GeV. See their Fig. 2.
13  CHATRCHYAN 2012V search for ${{\mathit A}^{0}}$ production in the decay ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ with 1.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV. A limit on $\sigma ({{\mathit A}^{0}})\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range ($1.5 - 7.5$) pb is given for ${\mathit m}_{{{\mathit A}^{0}}}$ = ($5.5 - 8.7$) and ($11.5 - 14$) GeV at 95$\%$ CL.
14  AALTONEN 2011P search in 2.7 fb${}^{-1}$ of ${{\mathit p}}{{\overline{\mathit p}}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 1.96 TeV for the decay chain ${{\mathit t}}$ $\rightarrow$ ${{\mathit b}}{{\mathit H}^{+}}$ , ${{\mathit H}^{+}}$ $\rightarrow$ ${{\mathit W}^{+}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ with ${\mathit m}_{{{\mathit A}^{0}}}$ between 4 and 9 GeV. See their Fig.$~$4 for limits on B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit b}}{{\mathit H}^{+}}$ ) for 90 $<$ ${\mathit m}_{{{\mathit H}^{+}}}<$ 160 GeV.
15  ABOUZAID 2011A search for the decay chain ${{\mathit K}_{{L}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ and give a limit B( ${{\mathit K}_{{L}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$ ) $\cdot{}$ B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) $<$ $1.0 \times 10^{-10}$ at 90$\%$ CL for ${\mathit m}_{{{\mathit A}^{0}}}$ = 214.3 MeV.
16  The search was motivated by PARK 2005 .
17  DEL-AMO-SANCHEZ 2011J search for the process ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit \Upsilon}{(1S)}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ with ${{\mathit A}^{0}}$ decaying to invisible final states. They give limits on B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ invisible) in the range ($1.9 - 4.5){\times }10^{-6}$ (90$\%$ CL) for 0 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 8.0 GeV, and ($2.7 - 37){\times }10^{-6}$ for 8.0 ${}\leq{}{\mathit m}_{{{\mathit A}^{0}}}{}\leq{}$ 9.2 GeV.
18  LEES 2011H search for the process ${{\mathit \Upsilon}{(2S,3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ decaying hadronically and give limits on B( ${{\mathit \Upsilon}{(2S,3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ hadrons) in the range $1 \times 10^{-6} - 8 \times 10^{-5}$ (90$\%$ CL) for 0.3 $<$ ${\mathit m}_{{{\mathit A}^{0}}}$ $<$ 7 GeV. The decay rates for ${{\mathit \Upsilon}{(2S)}}$ and ${{\mathit \Upsilon}{(3S)}}$ are assumed to be equal up to the phase space factor. See their Fig. 5.
19  ANDREAS 2010 analyze constraints from rare decays and other processes on a light ${{\mathit A}^{0}}$ with ${\mathit m}_{{{\mathit A}^{0}}}$ $<$ 2${\mathit m}_{{{\mathit \mu}}}$ and give limits on its coupling to fermions at the level of $10^{-4}$ times the Standard Model value.
20  HYUN 2010 search for the decay chain ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit K}^{*0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ and give a limit on B( ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit K}^{*0}}{{\mathit A}^{0}}$ ) $\cdot{}$ B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range ($2.26 - 5.53){\times }10^{-8}$ at 90$\%$CL for ${\mathit m}_{{{\mathit A}^{0}}}$ = $212 - 300$ MeV. The limit for ${\mathit m}_{{{\mathit A}^{0}}}$ = 214.3 MeV is $2.26 \times 10^{-8}$.
21  HYUN 2010 search for the decay chain ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit \rho}^{0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ and give a limit on B( ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit \rho}^{0}}{{\mathit A}^{0}}$ ) $\cdot{}$ B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range ($1.73 - 4.51){\times }10^{-8}$ at 90$\%$CL for ${\mathit m}_{{{\mathit A}^{0}}}$ = $212 - 300$ MeV. The limit for ${\mathit m}_{{{\mathit A}^{0}}}$ = 214.3 MeV is $1.73 \times 10^{-8}$.
22  AUBERT 2009P search for the process ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ for 4.03 $<$ ${\mathit m}_{{{\mathit A}^{0}}}<$ 9.52 and 9.61 $<$ ${\mathit m}_{{{\mathit A}^{0}}}<$ 10.10 GeV, and give limits on B( ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ ) in the range ($1.5 - 16){\times }10^{-5}$ (90$\%$ CL).
23  AUBERT 2009Z search for the process ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ for 0.212 $<$ ${\mathit m}_{{{\mathit A}^{0}}}$ $<$ 9.3 GeV and give limits on B( ${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range ($0.3 - 8){\times }10^{-6}$ (90$\%$ CL).
24  AUBERT 2009Z search for the process ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ for 0.212 $<$ ${\mathit m}_{{{\mathit A}^{0}}}$ $<$ 9.3 GeV and give limits on B( ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) in the range ($0.3 - 5){\times }10^{-6}$ (90$\%$ CL).
25  TUNG 2009 search for the decay chain ${{\mathit K}_{{L}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ and give a limit on B( ${{\mathit K}_{{L}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$ ) $\cdot{}$ B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ ) in the range ($2.4 - 10.7){\times }10^{-7}$ at 90$\%$CL for ${\mathit m}_{{{\mathit A}^{0}}}$ = $194.3 - 219.3$ MeV. The limit for ${\mathit m}_{{{\mathit A}^{0}}}$ = 214.3 MeV is $2.4 \times 10^{-7}$.
26  LOVE 2008 search for the process ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ with ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ (for ${\mathit m}_{{{\mathit A}^{0}}}$ $<$ 2${\mathit m}_{{{\mathit \tau}}}$) and ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ . Limits on B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ ) $\cdot{}$ B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ ) in the range $10^{-6} - 10^{-4}$ (90$\%$ CL) are given.
27  BESSON 2007 give a limit B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit \eta}_{{b}}}{{\mathit \gamma}}$ ) $\cdot{}$ B( ${{\mathit \eta}_{{b}}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ ) $<$ 0.27$\%$ (95$\%$ CL), which constrains a possible ${{\mathit A}^{0}}$ exchange contribution to the ${{\mathit \eta}_{{b}}}$ decay.
28  PARK 2005 found three candidate events for ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ in the HyperCP experiment. Due to a narrow spread in dimuon mass, they hypothesize the events as a possible signal of a new boson. It can be interpreted as a neutral particle with ${\mathit m}_{{{\mathit A}^{0}}}$ = $214.3$ $\pm0.5~$MeV and the branching fraction B( ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit A}^{0}}$ )$\cdot{}$B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) = ($3.1$ ${}^{+2.4}_{-1.9}$ $\pm1.5){\times }10^{-8}$.
29  BALEST 1995 give limits B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ ) < $1.5 \times 10^{-5}$ at 90$\%$ CL for ${\mathit m}_{{{\mathit A}^{0}}}<$ 5 GeV. The limit becomes $<10^{-4}$ for ${\mathit m}_{{{\mathit A}^{0}}}$ $<7.7$ GeV.
30  ANTREASYAN 1990C give limits B( ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$ ) < $5.6 \times 10^{-5}$ at 90$\%$ CL for ${\mathit m}_{{{\mathit A}^{0}}}<$ 7.2 GeV. ${{\mathit A}^{0}}$ is assumed not to decay in the detector.
References:
ABLIKIM 2022H
PR D105 012008 Search for a $CP$-odd light Higgs boson in $J/\psi \to \gamma A^0$
JIA 2022
PRL 128 081804 Search for a light Higgs boson in single-photon decays of $\Upsilon(1S)$ using $\Upsilon(2S) \to \pi^+ \pi^- \Upsilon(1S)$ tagging method
AAD 2020AE
PRL 125 221802 Search for Higgs Boson Decays into a $Z$ Boson and a Light Hadronically Decaying Resonance Using 13 TeV $pp$ Collision Data from the ATLAS Detector
AABOUD 2018AP
JHEP 1806 166 Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at $\sqrt{s}=13$ TeV
KHACHATRYAN 2017AZ
JHEP 1710 076 Search for Light Bosons in Decays of the 125 GeV Higgs Boson in Proton-Proton Collisions at $\sqrt {s }$ = 8 TeV
ABLIKIM 2016E
PR D93 052005 Search for a Light $\mathit CP$-odd Higgs Boson in Radiative Decays of ${{\mathit J / \psi}}$
KHACHATRYAN 2016F
JHEP 1601 079 Search for a Very Light NMSSM Higgs Boson Produced in Decays of the 125 GeV Scalar Boson and Decaying into ${{\mathit \tau}}$ leptons in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV
LEES 2015H
PR D91 071102 Search for a Light Higgs Resonance in Radiative Decays of the ${{\mathit \Upsilon}{(1S)}}$ with a Charm Tag
LEES 2013C
PR D87 031102 Search for di-Muon Decays of a Low-Mass Higgs Boson in Radiative Decays of the ${{\mathit \Upsilon}{(1S)}}$
LEES 2013R
PR D88 071102 Search for a Low-Mass Scalar Higgs Boson Decaying to a Tau Pair in Single-Photon Decays of ${{\mathit \Upsilon}{(1S)}}$
LEES 2013L
PR D88 031701 Search for a Light Higgs Boson Decaying to Two Gluons or ${\mathit {\mathit s}}{\mathit {\overline{\mathit s}}}$ in the Radiative Decays of ${{\mathit \Upsilon}{(1S)}}$
ABLIKIM 2012
PR D85 092012 Search for a Light Exotic Particle in ${{\mathit J / \psi}}$ Radiative Decays
CHATRCHYAN 2012V
PRL 109 121801 Search for a Light Pseudoscalar Higgs Boson in the Dimuon Decay Channel in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 7 TeV
AALTONEN 2011P
PRL 107 031801 Search for a Very Light $\mathit CP$-Odd Higgs Boson in Top Quark Decays from ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions at $\sqrt {s }$ = 1.96 TeV
ABOUZAID 2011A
PRL 107 201803 Search for the Rare Decays ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ and ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit X}^{0}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
DEL-AMO-SANCHEZ 2011J
PRL 107 021804 Search for Production of Invisible Final States in Single-Photon Decays of ${{\mathit \Upsilon}{(1S)}}$
LEES 2011H
PRL 107 221803 Search for Hadronic Decays of a Light Higgs Boson in the Radiative Decay ${{\mathit \Upsilon}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit A}^{0}}$
ANDREAS 2010
JHEP 1008 003 Constraints on a very Light $\mathit CP$-Odd Higgs of the NMSSM and other Axion-Like Particles
HYUN 2010
PRL 105 091801 Search for a Low Mass Particle Decaying into ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ in ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit K}^{*0}}{{\mathit X}}$ and ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit \rho}^{0}}{{\mathit X}}$ at Belle
AUBERT 2009P
PRL 103 181801 Search for a Low-Mass Higgs Boson in ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit A}^{0}}$ , ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ at BABAR
AUBERT 2009Z
PRL 103 081803 Search for Dimuon Decays of a Light Scalar Boson in Radiative Transitions ${{\mathit \Upsilon}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit A}^{0}}$
TUNG 2009
PRL 102 051802 Search for a Light Pseudoscalar Particle in the Decay ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit X}}$
LOVE 2008
PRL 101 151802 Search for Very Light $\mathit CP$-Odd Higgs Boson in Radiative Decays of ${{\mathit \Upsilon}{(1S)}}$
BESSON 2007
PRL 98 052002 First Observation of ${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ and Tests of Lepton Universality in ${{\mathit \Upsilon}}$ Decays
PARK 2005
PRL 94 021801 Evidence for the Decay ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$
BALEST 1995
PR D51 2053 ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit \gamma}}$ $+$ noninteracting particles
ANTREASYAN 1990C
PL B251 204 Limits on Axion and Light Higgs Boson Production in ${{\mathit \Upsilon}{(1S)}}$ Decays