For example, a positive pion ( ) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion ( ), is made of one up antiquark and one down quark.
12.
In 1978, based on the success of the track sensitive target neutrino programme spearheaded by Wilbur Venus, Kalmus proposed an experiment using this equipment, but instead of a neutrino beam, used a 70 GeV negative pion beam.
13.
However this is true only in a first approximation : If one considers the possibility that a positive and a negative pion are virtually related in the sense that they can annihilate and transform into a pair of two neutral pions ( or two photons ), i . e . a pair of identical particles, we are faced with a more complex situation, which has to be handled within the second quantisation approach.
