To each particle is associated an antiparticle with the same mass but opposite charge. As an example the partner of the negatively charged electron (e-) is the positron (e+) that has the same properties of the electron but a positive charge.
The simplest way to separate particles and antiparticles makes use of a magnetic field. Passing through a uniform magnetic field particles and anti-particles, i.e. particles with opposite charges, are bent in opposite directions. From the particle curvature (positive or negative) is possible to distinguish among electrons and positrons. From the radius of curvature we can measure the particle momentum.