June 2, 2023

New value for W boson mass dims 2022 hints of physics beyond Standard Model

New value for W boson mass dims 2022 hints of physics beyond Standard Model
New value for W boson mass dims 2022 hints of physics beyond Standard ModelNew value for W boson mass dims 2022 hints of physics beyond Standard Model
Enlarge / Event display of a W-boson candidate decaying into a muon and a muon neutrino inside the ATLAS experiment. The blue line shows the reconstructed track of the muon, and the red arrow denotes the energy of the undetected muon neutrino.
ATLAS Collaboration/CERN

It’s often said in science that extraordinary claims require extraordinary evidence. Recent measurements of the mass of the elementary particle known as the W boson provide a useful case study as to why. Last year, Fermilab physicists caused a stir when they reported a W boson mass measurement that deviated rather significantly from theoretical predictions of the so-called Standard Model of Particle Physics—a tantalizing hint of new physics. Others advised caution, since the measurement contradicted prior measurements.

That caution appears to have been warranted. The ATLAS collaboration at CERN’s Large Hadron Collider (LHC) has announced a new, improved analysis of their own W boson data and found the measured value for its mass was still consistent with Standard Model. Caveat: It’s a preliminary result. But it lessens the likelihood of Fermilab’s 2022 measurement being correct.

“The W mass measurement is among the most challenging precision measurements performed at hadron colliders,” said ATLAS spokesperson Andreas Hoecker. “It requires extremely accurate calibration of the measured particle energies and momenta, and a careful assessment and excellent control of modeling uncertainties. This updated result from ATLAS provides a stringent test, and confirms the consistency of our theoretical understanding of electroweak interactions.”

As we’ve reported previously, the Standard Model describes the basic building blocks of the Universe and how matter evolved. Those blocks can be divided into two basic clans: fermions and bosons. Fermions make up all the matter in the Universe and include leptons and quarks. Leptons are particles that are not involved with holding the atomic nucleus together, such as electrons and neutrinos. Their job is to help matter change through nuclear decay into other particles and chemical elements, using the weak nuclear force. Quarks make up the atomic nucleus.

Bosons are the ties that bind the other particles together. Bosons pass from one particle to another, and this gives rise to forces. There are four force-related “gauge bosons.” The gluon is associated with the strong nuclear force: it “glues” an atom’s nucleus together. The photon carries the electromagnetic force, which gives rise to light. The W and Z bosons carry the weak nuclear force and give rise to different types of nuclear decay. And then there is the Higgs boson, a manifestation of the Higgs field. The Higgs field is an invisible entity that pervades the Universe. Interactions between the Higgs field and particles help provide particles with mass, with particles that interact more strongly having larger masses.