#### Search for ${{\mathit A}^{0}}$ (Axion) Resonance in ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$

The limit is for $\Gamma\mathrm {( {{\mathit A}^{0}} \rightarrow {{\mathit e}^{+}} {{\mathit e}^{-}} )}\cdot{}\Gamma\mathrm {( {{\mathit A}^{0}} \rightarrow {{\mathit \gamma}} {{\mathit \gamma}} )}/\Gamma _{{\mathrm {total}}}$
VALUE ($10^{-3}$ eV) CL% DOCUMENT ID TECN  COMMENT
• • We do not use the following data for averages, fits, limits, etc. • •
$<0.18$ 95
 1994
CNTR ${\mathit m}_{{{\mathit A}^{0}}}=1.1$ MeV
$<1.5$ 95
 1994
CNTR ${\mathit m}_{{{\mathit A}^{0}}}=1.4$ MeV
$<12$ 95
 1994
CNTR ${\mathit m}_{{{\mathit A}^{0}}}=1.7$ MeV
$<6.6$ 95 1
 1991
CNTR ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.8$ MeV
$<4.4$ 95
 1991
CNTR ${\mathit m}_{{{\mathit A}^{0}}}$= $1.78 - 1.92$ MeV
2
 1989
CNTR
$<0.11$ 95 3
 1989
CNTR ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.062$ MeV
$<33$ 97
 1988
CNTR ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.580$ MeV
$<42$ 97
 1988
CNTR ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.642$ MeV
$<73$ 97
 1988
CNTR ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.782$ MeV
$<79$ 97
 1988
CNTR ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.832$ MeV
 1 TRZASKA 1991 also give limits in the range ($6.6 - 30){\times }10^{-3}~$eV (95$\%$CL) for ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.6 - 2.0~$MeV.
 2 FOX 1989 measured positron annihilation with an electron in the source material into two photons and found no signal at $1.062$ MeV ($<$ $9 \times 10^{-5}$ of two-photon annihilation at rest).
 3 Similar limits are obtained for ${\mathit m}_{{{\mathit A}^{0}}}$ = $1.045-1.085$ MeV.
References:
 VO 1994
PR C49 1551 Search for Resonance in Multiphoton Final States from Low Energy ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ Scattering
ZPHY A340 209 Limits for Two-Photon and ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ Decay Widths of Positron Electron Scattering Resonances for $\sqrt {s }$=1.78 to 1.92 MeV
PR C39 288 Search for Anomalous ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ Annihilation from ${}^{140}\mathrm {Pr}$
PRL 62 1091 Search for Resonances in the ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}$ Process in the Mass Region around 1.062 ${\mathrm {MeV}}/\mathit c{}^{2}$