  There is evidence of a second neutral pion from: (1) the anomalous branching
ratios in the reactions p-bar p -> pi pi and p-bar d -> pi pi N, and (2) the
1960's results of Tsai-Chu et al. for antinucleon annihilation stars in
emulsions. The anomaly of (1) is eliminated if the two neutral pions in the
reactions p-bar p -> pi_0 pi_0 and p-bar d -> pi_0 pi_0 n are not identical.
Tsai-Chu et al. observed a second neutral pion that ``decays more rapidly into
electron pairs with larger opening angles and more frequently into double
pairs.'' One antineutron annihilation event produced three neutral particles
(each with a mass of 135 +/- 14 MeV), and each decayed into four electrons with
much wider opening angles than those of the internal conversion electrons seen
in pi-zero decays. The larger opening angles and much more frequent double pair
production could be caused by neutral pions with a lifetime so short that they
sometimes decay into photon pairs before they can leave the annihilation
nucleus (e.g., Ag) of the emulsion. We discuss several methods of searching for
this second neutral pion.
