Highlighted is a small part of a complicated high energy neutrino event
in the Fermilab 15-foot bubble chamber filled with a
neon-hydrogen mixture.
A positron (red) from an electron-positron pair annihilates in flight,
producing a gamma-ray photon (orange) which later
(about 11 cm in the actual
bubble chamber) materialises into another electron (blue)-positron
(green) pair.
For full details of this event see Positron Annihilation in Flight.