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 search

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. • • •

ADACHI

2023

BEL2

${{\mathit \tau}}$ $\rightarrow$ ${{\mathit e}}{{\mathit A}^{0}}$, ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit A}^{0}}$

TUMASYAN

2023

CMS

${{\mathit H}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ $\rightarrow$ 4 ${{\mathit \gamma}}$

ABLIKIM

2022

BES3

${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

⁴

JIA

2022

BELL

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

⁵

AAD

2020

ATLS

${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit A}^{0}}$

⁶

AABOUD

2018

ATLS

${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$

⁷

KHACHATRYAN

2017

CMS

${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$

⁸

ABLIKIM

2016

BES3

${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

⁹

KHACHATRYAN

2016

CMS

${{\mathit H}^{0}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$

¹⁰

LEES

2015

BABR

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

¹¹

LEES

2013

BABR

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

¹²

LEES

2013

BABR

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

¹³

LEES

2013

BABR

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

¹⁴

ABLIKIM

2012

BES3

${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

¹⁵

CHATRCHYAN

2012

CMS

${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$

¹⁶

AALTONEN

2011

CDF

${{\mathit t}}$ $\rightarrow$ ${{\mathit b}}{{\mathit H}^{+}}$, ${{\mathit H}^{+}}$ $\rightarrow$ ${{\mathit W}^{+}}{{\mathit A}^{0}}$

¹⁷ ^{, 18}

ABOUZAID

2011

KTEV

${{\mathit K}_{{{L}}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$

¹⁹

DEL-AMO-SANCH..

2011

BABR

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

²⁰

LEES

2011

BABR

${{\mathit \Upsilon}{(2S,3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

²¹

ANDREAS

2010

RVUE

²² ^{, 18}

HYUN

2010

BELL

${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit K}^{*0}}{{\mathit A}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$

²³ ^{, 18}

HYUN

2010

BELL

${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit \rho}^{0}}{{\mathit A}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$

²⁴

AUBERT

2009

BABR

${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

²⁵

AUBERT

2009

BABR

${{\mathit \Upsilon}{(2S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

²⁶

AUBERT

2009

BABR

${{\mathit \Upsilon}{(3S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

²⁷ ^{, 18}

TUNG

2009

K391

${{\mathit K}_{{{L}}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit A}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$

²⁸

LOVE

2008

CLEO

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

²⁹

BESSON

2007

CLEO

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit \eta}_{{{b}}}}{{\mathit \gamma}}$

³⁰

PARK

2005

HYCP

${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit A}^{0}}$, ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$

³¹

BALEST

1995

CLE2

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

³²

ANTREASYAN

1990

CBAL

${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit \gamma}}$

¹ ADACHI 2023A search for flavor-changing ${{\mathit \tau}}$ decays ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit e}}{{\mathit A}^{0}}$ and ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit A}^{0}}$, with ${{\mathit A}^{0}}$ invisible, using 62.8 fb${}^{-1}$ of ${{\mathit e}^{+}}{{\mathit e}^{-}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 10.58 GeV. Limits on B( ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit e}}{{\mathit A}^{0}}$)/B( ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}}{{\mathit \nu}}$) in the range $1.1 \times 10^{-3} - 9.7 \times 10^{-3}$ (95$\%$ CL) and B( ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit A}^{0}}$)/B( ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit \nu}}{{\mathit \nu}}$) in the range $0.7 \times 10^{-3} - 12.2 \times 10^{-3}$ (95$\%$ CL) are given for ${\mathit m}_{{{\mathit A}^{0}}}$ = $0 - 1.6$ GeV. See their Fig. 2.

² TUMASYAN 2023AR search for the decay ${{\mathit H}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}}$ with ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ (detected as a merged photonlike object) using 136 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. Limits on B( ${{\mathit H}}$ $\rightarrow$ ${{\mathit A}^{0}}{{\mathit A}^{0}})\cdot{}B{}^{2}$( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$) in the range $0.9 \times 10^{-3} - 3.3 \times 10^{-3}$ (95$\%$ CL) are given for ${\mathit m}_{{{\mathit A}^{0}}}$ = $0.1 - 1.2$ GeV. See their Fig. 2.

³ 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.

⁴ 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.

⁵ 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.

⁶ 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.

⁷ 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.

⁸ 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.

⁹ 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.

¹⁰ 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.

¹¹ 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.

¹² 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 $2 \times 10^{-2}$ (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.

¹³ 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 $0.9 - 13$ (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.

¹⁴ 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.

¹⁵ 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.

¹⁶ 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.

¹⁷ 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.

¹⁸ The search was motivated by PARK 2005.

¹⁹ 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.

²⁰ 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.

²¹ 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.

²² 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 $2.26 \times 10^{-8}$.

²³ 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 $1.73 \times 10^{-8}$.

²⁴ 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).

²⁵ 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).

²⁶ 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).

²⁷ 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 $2.4 \times 10^{-7}$.

²⁸ 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.

²⁹ 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.

³⁰ 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( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$) = ($3.1$ ${}^{+2.4}_{-1.9}$ $\pm1.5){\times }10^{-8}$.

³¹ 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.

³² 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.

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2023A

PRL 130 181803

Search for Lepton-Flavor-Violating

?

Decays to a Lepton and an Invisible Boson at Belle II

TUMASYAN

2023AR

PRL 131 101801

Search for exotic Higgs boson decays H $\to$$\mathcal{A}\mathcal{A}$$\to$ 4$\gamma$ with events containing two merged diphotons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

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

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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

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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

2009Z

PRL 103 081803

Search for Dimuon Decays of a Light Scalar Boson in Radiative Transitions ${{\mathit \Upsilon}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit A}^{0}}$

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

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