The key feature of this picture is a `vee' (a neutral particle decaying into a pair of particles of opposite charge) pointing to a kink (the decay of a charged particle) on a track that has already kinked (very slightly) once. (The actual distance to the first kink is 5.5 cm)
The `vee' was by measurement identified as a lambda zero that could only have come from the second kink.
Analysis of the full measurement enabled the omega minus and xi minus masses to be verified and the event identified as
K- + proton --> omega minus + K+ + k)
followed by the decays
omega minus --> xi minus + pi0,
xi minus --> lambda pi- and
lambda --> p pi-
This picture was taken in the 1.5 metre British National Bubble chamber, exposed to a 6 GeV/c K- beam. For further details see D C Colley et al, Physics Letters 19 2 (1965)