The does not leave a track because it is not charged. You can nevertheless know that there must be either a , , or a , because there exists a "VEE" pointing to the initial interaction of the proton and . Only 4 particles can decay to a VEE:

The two first  decay into the same particles, so they cannot be distinguished. The second two give different particles and can be excluded. See the overall explanation of the different processes engaged here.