GENEVA — Physicists working at the world’s biggest atom smasher detected the simultaneous production of three fundamental particles, a rare process that plays a key role in radioactivity and the Sun’s thermonuclear process.
The announcement from the European Organization for Nuclear Research, or CERN, at a conference in Italy confirmed another important element of the prevailing theory for how the universe began and how its most elemental pieces fit together.
In 2012, CERN hailed the discovery of a “missing cornerstone of physics” when it detected a new subatomic particle, the Higgs boson, that helps explain why all matter has mass. Its existence was predicted nearly a half-century earlier.
Now, the ATLAS team of collaborators at the Geneva-based Large Hadron Collider — which sends protons crashing into each other at nearly the speed of light in a circular 27-kilometer underground tunnel — has come across three W or Z bosons in proton–proton collisions.
“The W and Z bosons are the mediator particles of the weak force — one of the four known fundamental forces — which is responsible for the phenomenon of radioactivity as well as an essential ingredient to our Sun’s thermonuclear process,” ATLAS said in a statement.
CERN, which operates the LHC beneath ground along the Swiss-French border near Geneva, aims to recreate conditions a split second after the Big Bang, which scientists theorize was the massive explosion that created the universe.
Since last year the collider has been going through a major upgrade to increase the number of proton collisions for experiments, which boosts the probability of more discoveries about the universe’s fundamental properties.
[Physics Briefing] ATLAS finds evidence for the simultaneous production of three W or Z bosons in LHC collisions. Learn more about this new result, presented today at the #Moriond conference: https://t.co/oIoyZJvq8I pic.twitter.com/CzmTlqr9Bx
— ATLAS Experiment (@ATLASexperiment) March 17, 2019
Rare processes
The latest finding involves tri-boson production under the standard model of particle physics, a well-tested theory developed in the early 1970s that explains how the basic building blocks of matter interact.
“Tri-boson production are rare processes predicted by the Standard Model of particle physics,” ATLAS said. “Their production involves self-interaction among the weak bosons, so-called triple and quartic gauge boson couplings, which are sensitive to possible contributions from yet unknown particles or forces.”
Since the 1930s, physicists have accepted that everything in the universe is made from a few basic building blocks called fundamental particles, governed by fundamental forces.
But the standard model describes only about 5 percent of the universe. Scientists believe that objects gain their size and shape when particles interact in an energy field with the Higgs boson.
Since weak bosons are unstable, they are reconstructed in the LHC detector by their decays to pairs of leptons, including invisible neutrinos, or quarks, which form sprays of particles called “jets,” ATLAS said.
“Altogether, the resulting ATLAS measurement is found to be in agreement with the Standard Model prediction,” it said, “thus providing one more piece of the puzzle in our understanding of particle physics.”
