Possible Clues:

• Antiparticle of the electron
• Assert Collider finally working -- here's a particle
• Particle one found in smashing protons
• Particle discovered by Carl David Anderson in 1932
• A tiny thing to put forward, and not back
• Particle, when realigned, is right on top
• Antiparticle first observed in 1929
• Elementary particle with positive charge
• Particle, larger than normal, has it in for most common of neutrinos
• Correct, sport — ion is a particle