W and Z bosons
The W and Z bosons are elementary particles that carry the weak interaction, one of the four fundamental forces of nature. There are three of them: two electrically charged W bosons, W+ and W−, and one neutral Z boson, Z0.[1] The other neutral carrier in the same theory is the massless photon, the particle of light.[1]
What they do
Particles of matter can interact by exchanging these bosons, but only over very short distances. With an electric charge of +1 or −1, the W boson can change one kind of particle into another. This makes it responsible for many nuclear processes, including those that let stars shine.[2] Examples of the weak force at work, according to the Nobel committee, are some kinds of radioactive decay and the nuclear processes that power the Sun.[3]
The W boson is the fourth heaviest particle in the Standard Model of particle physics.[4]
Discovery
The particles were found at CERN. Following an idea presented by Carlo Rubbia and others, CERN converted one of its accelerators, the Super Proton Synchrotron (SPS), into a machine that collided protons with antiprotons with enough energy to make W and Z bosons. This was made possible by a method for controlling particle beams, called stochastic cooling, invented by Simon van der Meer.[5] In January 1983 two teams of scientists, called UA1 and UA2, reported the first signs of the W boson, and CERN announced the discovery on 25 January 1983.[6] At a seminar on 22 January 1983 the UA2 team said its detector had recorded four possible W boson events. UA2 went on to make the most accurate measurements of the masses of the W and Z of its time.[7] The discovery of the Z boson was also announced in 1983.[8]
The 1984 Nobel Prize in Physics was awarded to Carlo Rubbia and Simon van der Meer "for their decisive contributions to the large project, which led to the discovery of the field particles W and Z, communicators of weak interaction".[9]
References
- ↑ 1.0 1.1 "Press release: The 1984 Nobel Prize in Physics". Royal Swedish Academy of Sciences, via NobelPrize.org. 17 October 1984. Retrieved 20 October 2026.
Besides the two heavy charged communicators W+ and W–, the theory contains two neutral communicators – one heavy, the other massless. The massless one is the photon. The heavy Z0 represents something completely new.
- ↑ "W boson: Sunshine and stardust". CERN. Retrieved 20 October 2026.
Particles of matter can interact by exchanging these bosons, but only over short distances. With a charge of +1 or -1, the W boson can change the identity of particles. It is responsible for many nuclear processes, including those letting stars burn.
- ↑ "Press release: The 1984 Nobel Prize in Physics". Royal Swedish Academy of Sciences, via NobelPrize.org. 17 October 1984. Retrieved 20 October 2026.
Examples of weak processes are radioactive ... decays and also the nuclear processes in the sun which control its power.
- ↑ "W boson: Sunshine and stardust". CERN. Retrieved 20 October 2026.
The W boson is the fourth heaviest particle in the Standard Model and its mass is reliant on the Brout-Englert-Higgs mechanism.
- ↑ "W boson: Sunshine and stardust". CERN. Retrieved 20 October 2026.
The discovery was due to an idea that Rubbia and others had presented: converting the SPS into a proton anti-proton collider with the necessary energy to produce the W and Z bosons. This conversion was made possible by Simon van der Meer's invention of stochastic cooling.
- ↑ "W boson: Sunshine and stardust". CERN. Retrieved 20 October 2026.
CERN announced the discovery of the W boson on 25 January 1983. Two collaborations, UA1, led by Carlo Rubbia, and UA2 led by Pierre Darriulat, presented their observation in seminars a few days earlier.
- ↑ "UA2". CERN. Retrieved 20 October 2026.
UA2 provided the most accurate measurements of the W and Z masses ... At a seminar on 22 January 1983, UA2 physicist Luigi Di Lella announced to a packed CERN auditorium that the UA2 detector had recorded four events that were candidates for a W boson.
- ↑ "Press release: The 1984 Nobel Prize in Physics". Royal Swedish Academy of Sciences, via NobelPrize.org. 17 October 1984. Retrieved 20 October 2026.
The discovery of the W and Z were announced in 1983 by Rubbia and collaborating large teams of scientists ... The project at CERN, the European nuclear research organization
- ↑ "Press release: The 1984 Nobel Prize in Physics". Royal Swedish Academy of Sciences, via NobelPrize.org. 17 October 1984. Retrieved 20 October 2026.
for their decisive contributions to the large project, which led to the discovery of the field particles W and Z, communicators of weak interaction