• • • We do not use the following data for averages, fits, limits, etc. • • • |
$<2 \times 10^{-10}$ |
95 |
1 |
|
LHCB |
$<3.7 \times 10^{-8}$ |
90 |
2 |
|
KOTO |
$<6 \times 10^{-11}$ |
90 |
3 |
|
NA48 |
|
|
4 |
|
BELL |
$<1 \times 10^{-9}$ |
95 |
5 |
|
LHCB |
$<1.5 \times 10^{-6}$ |
90 |
6 |
|
WASA |
$<2$ |
90 |
7 |
|
KLOE |
|
|
8 |
|
KLOE |
$<2 \times 10^{-15}$ |
90 |
9 |
|
BDMP |
$<3 \times 10^{-14}$ |
90 |
10 |
|
BDMP |
$<7 \times 10^{-10}$ |
90 |
11 |
|
B787 |
$<7.3 \times 10^{-11}$ |
90 |
12 |
|
B949 |
$<4.5 \times 10^{-11}$ |
90 |
13 |
|
B787 |
$<4 \times 10^{-5}$ |
90 |
14 |
|
B787 |
$<4.9 \times 10^{-5}$ |
90 |
|
|
CLEO |
$<5.3 \times 10^{-5}$ |
90 |
|
|
CLEO |
$<3.3 \times 10^{-5}$ |
90 |
15 |
|
NOMD |
$<5.0 \times 10^{-8}$ |
90 |
16 |
|
B787 |
$<5.2 \times 10^{-10}$ |
90 |
17 |
|
B787 |
$<2.8 \times 10^{-4}$ |
90 |
18 |
|
CBAR |
$<3 \times 10^{-4}$ |
90 |
18 |
|
CBAR |
$<4 \times 10^{-5}$ |
90 |
18 |
|
CBAR |
$<6 \times 10^{-5}$ |
90 |
18 |
|
CBAR |
$<6 \times 10^{-5}$ |
90 |
18 |
|
CBAR |
$<7 \times 10^{-3}$ |
90 |
19 |
|
CNTR |
$<2 \times 10^{-3}$ |
90 |
19 |
|
CNTR |
$<2 \times 10^{-7}$ |
90 |
20 |
|
B787 |
$<3 \times 10^{-13}$ |
|
21 |
|
COSM |
$<1.1 \times 10^{-8}$ |
90 |
22 |
|
SPEC |
$<5 \times 10^{-4}$ |
90 |
23 |
|
B787 |
$<1 \times 10^{-12}$ |
95 |
24 |
|
BDMP |
$<1 \times 10^{-12}$ |
95 |
25 |
|
BDMP |
$<1 \times 10^{-11}$ |
95 |
26 |
|
BDMP |
$<1 \times 10^{-14}$ |
95 |
27 |
|
BDMP |
$<4 \times 10^{-6}$ |
90 |
28 |
|
SPEC |
$<1 \times 10^{-7}$ |
90 |
29 |
|
B787 |
$<1.3 \times 10^{-8}$ |
90 |
30 |
|
SPEC |
$<1 \times 10^{-9}$ |
90 |
31 |
|
SPEC |
$<2 \times 10^{-5}$ |
90 |
32 |
|
SPEC |
$<(1.5-4){\times }\text{ 10^}{-6}$ |
90 |
32 |
|
SPEC |
|
|
33 |
|
CNTR |
|
|
34 |
|
CNTR |
|
|
35 |
|
|
1
The limit is for ${\mathit \tau}_{{{\mathit X}^{0}}}$ = 10 ps. See their Fig. 4 for limits in the range of ${\mathit m}_{{{\mathit X}^{0}}}$ = $250 - 4700$ MeV and ${\mathit \tau}_{{{\mathit X}^{0}}}$ = $0.1 - 1000$ ps.
|
2
The limit as a function of ${\mathit m}_{{{\mathit X}^{0}}}$ from 0 to 250 MeV is provided in their Fig. 5 .
|
3
The limit is for ${\mathit m}_{{{\mathit X}^{0}}}$ = 216 MeV and ${\mathit \tau}_{{{\mathit X}^{0}}}{}\leq{}$ 10 ps. See their Fig. 4(c) for limits in the range of ${\mathit m}_{{{\mathit X}^{0}}}$ = $211 - 354$ MeV and longer lifetimes.
|
4
WON 2016 look for a vector boson coupled to baryon number. Derived limits on ${{\mathit \alpha}^{\,'}}$ $<$ for ${\mathit m}_{{{\mathit X}^{0}}}$ = $290 - 520$ MeV at 95$\%$ CL. See their Fig. 4 for mass-dependent limits.
|
5
The limit is for ${\mathit \tau}_{{{\mathit X}^{0}}}$ = 10 ps and ${\mathit m}_{{{\mathit X}^{0}}}$ = $214 - 4350$ MeV. See their Fig. 4 for mass- and lifetime-dependent limits.
|
6
Limits between $2.0 \times 10^{-5}$ and $1.5 \times 10^{-6}$ are obtained for ${\mathit m}_{{{\mathit X}^{0}}}$ = $20 - 100$ MeV (see their Fig. 8). Angular momentum conservation requires that ${{\mathit X}^{0}}$ has spin ${}\geq{}$ 1.
|
7
The limit is for B( ${{\mathit \phi}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit X}^{0}}$ )$\cdot{}$B( ${{\mathit X}^{0}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}$ ) and applies to ${\mathit m}_{{{\mathit X}^{0}}}$ = 410 MeV. It is derived by analyzing ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ and ${{\mathit \pi}^{-}}{{\mathit \pi}^{+}}{{\mathit \pi}^{0}}$ . Limits between $1 \times 10^{-6}$ and $2 \times 10^{-8}$ are obtained for ${\mathit m}_{{{\mathit X}^{0}}}{}\leq{}$ 450 MeV (see their Fig. 6).
|
8
ARCHILLI 2012 analyzed ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ decays. Derived limits on ${{\mathit \alpha}^{\,'}}/{{\mathit \alpha}}$ $<$ $2 \times 10^{-5}$ for ${\mathit m}_{{{\mathit X}^{0}}}$ = $50 - 420$ MeV at 90$\%$ CL. See their Fig. 8 for mass-dependent limits.
|
9
This limit is for B( ${{\mathit \pi}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit X}^{0}}$ )$\cdot{}$B( ${{\mathit X}^{0}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}$ ) and applies for ${\mathit m}_{{{\mathit X}^{0}}}$ = 90 MeV and ${\mathit \tau}_{{{\mathit X}^{0}}}$ $\simeq{}$ $1 \times 10^{-8}$ sec. Limits between $10^{-8}$ and $2 \times 10^{-15}$ are obtained for ${\mathit m}_{{{\mathit X}^{0}}}$ = $3 - 120$ MeV and ${\mathit \tau}_{{{\mathit X}^{0}}}$ = $1 \times 10^{-11} - 1$ sec. See their Fig. 3 for limits at different masses and lifetimes.
|
10
This limit is for B( ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit X}^{0}}$ )$\cdot{}$B( ${{\mathit X}^{0}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}$ ) and applies for ${\mathit m}_{{{\mathit X}^{0}}}$ = 100 MeV and ${\mathit \tau}_{{{\mathit X}^{0}}}$ $≅$ $6 \times 10^{-9}$ sec. Limits between $10^{-5}$ and $3 \times 10^{-14}$ are obtained for ${\mathit m}_{{{\mathit X}^{0}}}{ {}\lesssim{} }$ 550 MeV and ${\mathit \tau}_{{{\mathit X}^{0}}}$ = $10^{-10} - 10$ sec. See their Fig. 5 for limits at different mass and lifetime and for ${{\mathit \eta}^{\,'}}$ decays.
|
11
This limit applies for a mass near 180 MeV. For other masses in the range ${\mathit m}_{{{\mathit X}^{0}}}$ = $150 - 250$ MeV the limit is less restrictive, but still improves ADLER 2002C and ATIYA 1993B.
|
12
ANISIMOVSKY 2004 bound is for ${\mathit m}_{{{\mathit X}^{0}}}$=0.
|
13
ADLER 2002C bound is for ${\mathit m}_{{{\mathit X}^{0}}}<$60 MeV. See Fig.$~$2 for limits at higher masses.
|
14
The quoted limit is for ${\mathit m}_{{{\mathit X}^{0}}}$ = $0 - 80$ MeV. See their Fig. 5 for the limit at higher mass. The branching fraction limit assumes pure phase space decay distributions.
|
15
ALTEGOER 1998 looked for ${{\mathit X}^{0}}$ from ${{\mathit \pi}^{0}}$ decay which penetrate the shielding and convert to ${{\mathit \pi}^{0}}$ in the external Coulomb field of a nucleus.
|
16
KITCHING 1997 limit is for B( ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit X}^{0}}$ )$\cdot{}$B( ${{\mathit X}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ ) and applies for ${\mathit m}_{{{\mathit X}^{0}}}\simeq{}$50 MeV, $\tau _{{{\mathit X}^{0}}}<10^{-10}~$s. Limits are provided for 0$<{\mathit m}_{{{\mathit X}^{0}}}<100$ MeV, $\tau _{{{\mathit X}^{0}}}<10^{-8}~$s.
|
17
ADLER 1996 looked for a peak in missing-mass distribution. This work is an update of ATIYA 1993 . The limit is for massless stable ${{\mathit X}^{0}}$ particles and extends to ${\mathit m}_{{{\mathit X}^{0}}}$=80 MeV at the same level. See paper for dependence on finite lifetime.
|
18
AMSLER 1994B and AMSLER 1996B looked for a peak in missing-mass distribution.
|
19
The MEIJERDREES 1994 limit is based on inclusive photon spectrum and is independent of ${{\mathit X}^{0}}$ decay modes. It applies to $\tau\mathrm {({{\mathit X}^{0}})}>10^{-23}~$sec.
|
20
ATIYA 1993B looked for a peak in missing mass distribution. The bound applies for stable ${{\mathit X}^{0}}$ of ${\mathit m}_{{{\mathit X}^{0}}}=150 - 250$ MeV, and the limit becomes stronger ($10^{-8}$) for ${\mathit m}_{{{\mathit X}^{0}}}=180 - 240$ MeV.
|
21
NG 1993 studied the production of ${{\mathit X}^{0}}$ via ${{\mathit \gamma}}$ ${{\mathit \gamma}}$ $\rightarrow$ ${{\mathit \pi}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit X}^{0}}$ in the early universe at $\mathit T\simeq{}$1 MeV. The bound on extra neutrinos from nucleosynthesis $\Delta {{\mathit N}_{{\nu}}}<0.3$ (WALKER 1991 ) is employed. It applies to ${\mathit m}_{{{\mathit X}^{0}}}{}\ll$1 MeV in order to be relativistic down to nucleosynthesis temperature. See paper for heavier ${{\mathit X}^{0}}$.
|
22
ALLIEGRO 1992 limit applies for ${\mathit m}_{{{\mathit X}^{0}}}=150 - 340$ MeV and is the branching ratio times the decay probability. Limit is $<1.5 \times 10^{-8}$ at 99$\%$CL.
|
23
ATIYA 1992 looked for a peak in missing mass distribution. The limit applies to ${\mathit m}_{{{\mathit X}^{0}}}=0 - 130$ MeV in the narrow resonance limit. See paper for the dependence on lifetime. Covariance requires ${{\mathit X}^{0}}$ to be a vector particle.
|
24
BARABASH 1992 is a beam dump experiment that searched for a light Higgs. Limits between $1 \times 10^{-12}$ and $1 \times 10^{-7}$ are obtained for 3 $<$ ${\mathit m}_{{{\mathit X}^{0}}}$ $<$ 40 MeV.
|
25
Limits between $1 \times 10^{-12}$ and $1$ are obtained for 4 $<$ ${\mathit m}_{{{\mathit X}^{0}}}$ $<$ 69 MeV.
|
26
Limits between $1 \times 10^{-11}$ and $5 \times 10^{-3}$ are obtained for 4 $<$ ${\mathit m}_{{{\mathit X}^{0}}}$ $<$ 63 MeV.
|
27
Limits between $1 \times 10^{-14}$ and $1$ are obtained for 3 $<$ ${\mathit m}_{{{\mathit X}^{0}}}$ $<$ 82 MeV.
|
28
MEIJERDREES 1992 limit applies for ${\mathit \tau}_{{{\mathit X}^{0}}}$ = $10^{-23} - 10^{-11}~$sec. Limits between $2 \times 10^{-4}$ and $4 \times 10^{-6}$ are obtained for ${\mathit m}_{{{\mathit X}^{0}}}$ = $25 - 120$ MeV. Angular momentum conservation requires that ${{\mathit X}^{0}}$ has spin ${}\geq{}$1.
|
29
ATIYA 1990B limit is for B( ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit X}^{0}}$ )$\cdot{}$B( ${{\mathit X}^{0}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ ) and applies for ${\mathit m}_{{{\mathit X}^{0}}}$ = 50 MeV, ${\mathit \tau}_{{{\mathit X}^{0}}}$ $<$ $10^{-10}~$s. Limits are also provided for 0 $<$ ${\mathit m}_{{{\mathit X}^{0}}}$ $<$ 100 MeV, ${\mathit \tau}_{{{\mathit X}^{0}}}$ $<$ $10^{-8}~$s.
|
30
KORENCHENKO 1987 limit assumes ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.7$ MeV, ${\mathit \tau}_{{{\mathit A}^{0}}}{ {}\lesssim{} }$ $10^{-12}$ s, and B( ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}$ ) = 1.
|
31
EICHLER 1986 looked for ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit A}^{0}}$ followed by ${{\mathit A}^{0}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}$ . Limits on the branching fraction depend on the mass and and lifetime of ${{\mathit A}^{0}}$. The quoted limits are valid when $\tau\mathrm {({{\mathit A}^{0}})}{ {}\gtrsim{} }3. \times 10^{-10}$s if the decays are kinematically allowed.
|
32
YAMAZAKI 1984 looked for a discrete line in ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \pi}^{+}}$ X. Sensitive to wide mass range (5$-$300 MeV), independent of whether X decays promptly or not.
|
33
ASANO 1982 at KEK set limits for B( ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit X}^{0}}$ ) for ${\mathit m}_{{{\mathit X}^{0}}}$ $<$100 MeV as BR $<4. \times 10^{-8}$ for $\tau\mathrm {( {{\mathit X}^{0}} \rightarrow {{\mathit n}} )}$ $>1. \times 10^{-9}$ s, BR $<1.4 \times 10^{-6}$ for $\tau $ $<1. \times 10^{-9}$s.
|
34
ASANO 1981B is KEK experiment. Set B( ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit X}^{0}}$ ) $<3.8 \times 10^{-8}$ at CL = 90$\%$.
|
35
ZHITNITSKII 1979 argue that a heavy axion predicted by YANG 1978 (3 $<\mathit m$ $<$40 MeV) contradicts experimental muon anomalous magnetic moments.
|