One of the three fundamental particles that transmit the weak force. (An example of a weak interaction process is nuclear beta decay.) These elementary particles—the W⁺, W⁻, and Z⁰ particles—were discovered in 1983 in very high energy proton-antiproton collisions. It is through the exchange of W and Z bosons that two particles interact weakly, just as it is through the exchange of photons that two charged particles interact electromagnetically. The intermediate vector bosons were postulated to exist in the 1960s; however, their large masses prevented their production and study at accelerators until 1983. Their discovery was a key step toward unification of the weak and electromagnetic interactions.