ANTIMATTER
Antimatter particles can be defined by their negative baryon number or lepton number, while "normal" (non-antimatter) matter particles have a positive baryon or lepton number. These two classes of particles are the antiparticle partners of one another.
Properties
There are compelling theoretical reasons to believe that, aside from the fact that antiparticles have different signs on all charges (such as electric charge and spin), matter and antimatter have exactly the same properties.[14][15] This means a particle and its corresponding antiparticle must have identical masses and decay lifetimes (if unstable). It also implies that, for example, a star made up of antimatter (an "antistar") will shine just like an ordinary star.[16] This idea was tested experimentally in 2016 by the ALPHA experiment, which measured the transition between the two lowest energy states of antihydrogen. The results, which are identical to that of hydrogen, confirmed the validity of quantum mechanics for antimatter.
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