The W boson is a fundamental particle. It is the fourth heaviest particle in the Standard Model and its mass depends on the Brout-Englert-Higgs mechanism.

The mass of the W boson is one of the most interesting fundamental parameters of the Standard Model of particle physics, as it allows model-independent probes for the effects of new physics.

ATLAS captured a sample of W bosons when the LHC was operating in 2011 with a collision energy of 7 TeV. In 2017 ATLAS published its first measurement of the W boson mass. With an uncertainty of 19 MeV, the mass of the W boson came to 80370 MeV.

In a new study, apart from the most recent measurement from the CDF experiment at the Tevatron, a former accelerator at Fermilab, the new ATLAS measurement matches and is more accurate than any previous W mass measurement.

The measurement is based on a reanalysis of a sample of 14 million W boson candidates produced in proton-proton collisions at the Large Hadron Collider (LHC), CERN’s main particle accelerator.

In its latest study, ATLAS reanalyzed its 2011 sample of W bosons to improve the accuracy of its previous measurements. The new W boson mass, 80360 MeV with an uncertainty of 16 MeV, is 10 MeV lower and 16% more accurate than the previous ATLAS finding. The result corresponds to the Standard Model.

ATLAS spokesman Andreas Hoecker said: “To achieve this result, ATLAS used an advanced data-fitting technique to determine the mass, as well as more recent, improved versions of what are known as the proton’s parton distribution functions. These functions describe the sharing of the proton’s momentum among its component quarks and gluons. In addition, ATLAS verified the theoretical description of the W boson production process using special LHC proton-proton runs.”

“Because of an undetected neutrino in the decay of the particle, the W mass measurement is among the most challenging precision measurements performed on hadron colliders. It requires extremely accurate calibration of the measured particle energies and impulses and careful assessment and excellent control of model uncertainties. This updated result from ATLAS provides a rigorous test and confirms the consistency of our theoretical understanding of electroweak interactions.”

Magazine reference:

  1. The ATLAS Collaboration. Improved mass measurement of the W boson using 7 TeV proton-proton collisions with the ATLAS detector.