First high-precision LHC measurement of W boson mass

World science, 14 February 2018

The ATLAS collaboration published the article on the first high-precision measurement of the mass of the W boson at the Large Hadron Collider (LHC) in CERN. The W boson is one of two elementary particles that mediates the weak interaction (one of the fundamental interactions). The reported result gives a value of 80370±19 MeV for the W mass is consistent with the expectation from the Standard Model of Particle Physics, a theory that describes known particles and their interactions.

The measurement is based on about 14 million W bosons recorded in a single year (2011), when the LHC was running at the energy of 7 TeV. It matches previous measurements obtained at LEP, the ancestor of the LHC at CERN, and at the Tevatron, a former accelerator at Fermilab in the United States, data of which made it possible to continuously refine this measurement over the last 20 years.

The W boson is one of the heaviest known particles in the universe. Its discovery in 1983 crowned the success of CERN’s Super proton-antiproton Synchrotron, leading to the Nobel Prize in physics in 1984. Although the properties of the W boson have been studied for more than 30 years, measuring its mass to high precision remains a major challenge.

“Achieving such a precise measurement despite the demanding conditions present in a hadron collider such as the LHC is a great challenge,” said the physics coordinator of the ATLAS Collaboration, Tancredi Carli. “Reaching similar precision, as previously obtained at other colliders, with only one year of Run 1 data is remarkable. It is an extremely promising indication of our ability to improve our knowledge of the Standard Model and look for signs of new physics through highly accurate measurements.”