and antiparticle [Photo: CERN]
The CERN experiment ACACUSA has weighed antiprotons to an unprecedented level of accuracy. The results, published in Nature , do not reveal a significant difference in mass between the antiproton and its proton counterpart.
Though this answer is to be expected based on current physics, it does not help understand why matter dominates almost exclusively over anti-matter in our universe. This preponderance of matter over anti-matter is one of the main unknowns in contemporary physics.