It is with great pleasure that we can announce that Nature has published our work on the measurement of the W boson mass with the CMS experiment. It is a rare occurrence that CMS publishes in Nature—I can only find 3 other cases out of well over 1000 publications—which makes it even more exciting. Of course with the very long review time—we did announce the measurement on September 17, 2024—the publication feels oddly anti-climactic. The measurement is the most precise one from any LHC experiment, agrees perfectly with the predicted value and maybe unfortunately puts the mystery of the discrepant measurement by CDF to rest. It also made the MIT News by the way.
I would like to take the opportunity and point out that this has been a wonderful journey with the CMS colleagues and a group of dedicated theorists. This has been a monumental effort, a big thank you to the team!
As it is our tradition I would like to highlight the contributions from the MIT group. Clearly, the intellectual leader was our own Joshua Bendavid (MIT, PhD 2013). He took care of the heart of the measurement which is the momentum scale calibration and overall software optimization to make the huge fits even feasible. Kenneth Long worked closely with our theory colleagues to make sure the theoretical uncertainties would not blow up too much. A tricky task that required many in-depth studies; he also had to take charge at times keeping Josh on track not to loose sight of the big picture. Kenneth has meanwhile moved on to a permanent researcher position at CNRS, Lyon. Jan Eysermans joined the team last, but took on the detailed calibration of the hadronic recoil which even as a second order effect in the isolation criteria, could have spoiled the measurement. With his work he also laid the foundation for the use of the transverse mass which will carry our analysis to the next level. He was a crucial mover to convince CMS to run at low luminosity in 2026 to have a clean dataset to verify we can move to that next level.
Last but not least we had Tianyu (Justin) Yang who wrote his full thesis on the topic helping out with detailed studies of the PDFs. His thesis defense happened end of August, before the September seminar, and the thesis committee had to approve the thesis without knowing the final number, which was added at time of submission. This is the first thesis in the group that was actually embargoed for three months. Justin has moved on to the Rutgers Cancer Institute as Radiation Oncology Physics Resident.
It remains to point out that we have not been resting on our laurels meanwhile. The recent Pisa workshop and the big electroweak precision workshop planned for the summer at the LPC@Fermilab are a testament to our commitment. Join the workshop and join the effort! We have a lot of work ahead of us with all the great tools that have been developed in this Herculean effort.