Editing Antiparticle (section)

=== Experiment ===

In 1932, soon after the prediction of [[positron]]s by [[Paul Dirac]], [[Carl D. Anderson]] found that cosmic-ray collisions produced these particles in a [[cloud chamber]] – a [[particle detector]] in which moving [[electron]]s (or positrons) leave behind trails as they move through the gas. The electric charge-to-mass ratio of a particle can be measured by observing the radius of curling of its cloud-chamber track in a [[magnetic field]]. Positrons, because of the direction that their paths curled, were at first mistaken for electrons travelling in the opposite direction.  Positron paths in a cloud-chamber trace the same helical path as an electron but rotate in the opposite direction with respect to the magnetic field direction due to their having the same magnitude of charge-to-mass ratio but with opposite charge and, therefore, opposite signed charge-to-mass ratios.

The [[antiproton]] and [[antineutron]] were found by [[Emilio Segrè]] and [[Owen Chamberlain]] in 1955 at the [[University of California, Berkeley]].<ref>{{cite web|url=https://www.nobelprize.org/prizes/physics/1959/summary/|title=The Nobel Prize in Physics 1959}}</ref> Since then, the antiparticles of many other subatomic particles have been created in particle accelerator experiments. In recent years, complete atoms of [[antimatter]] have been assembled out of antiprotons and positrons, collected in electromagnetic traps.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/11/101118-antimatter-trapped-engines-bombs-nature-science-cern/|archive-url=https://web.archive.org/web/20101120181454/http://news.nationalgeographic.com/news/2010/11/101118-antimatter-trapped-engines-bombs-nature-science-cern/|url-status=dead|archive-date=November 20, 2010|title=Antimatter Atoms Trapped for First Time – 'A Big Deal'|date=19 November 2010}}</ref>