High-precision measurement of the W boson mass with the CMS experiment

TL;DR

This paper reports a highly precise measurement of the W boson mass using CMS data from 2016, testing the standard model's predictions and addressing recent experimental challenges.

Contribution

First measurement of the W boson mass at 13 TeV with unprecedented precision using CMS data, providing a critical test of the standard model.

Findings

Measured W mass: 80 360.2 ± 9.9 MeV.

Result agrees with the standard model prediction.

Improved experimental and theoretical constraints used.

Abstract

In the standard model of particle physics, the masses of the W and Z bosons, the carriers of the weak interaction, are uniquely related. A precise determination of their masses is important because quantum loops of heavy, undiscovered particles could modify this relationship. Although the Z mass is known to the remarkable precision of 22 parts per million (2.0 MeV), the W mass is known much less precisely. A global fit to measured electroweak observables predicts the W mass with 6 MeV uncertainty [1$-$3]. Reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model, made even more urgent by a recent challenge to the global fit prediction by a measurement from the CDF Collaboration at the Fermilab Tevatron collider [4]. Here we report the measurement of the W mass by the CMS Collaboration at the CERN LHC, based on a large data sample of W $\to$ $\mu\nu$ events collected in 2016 at the proton-proton collision energy of 13 TeV. The measurement exploits a high-granularity maximum likelihood fit to the kinematic properties of muons produced in W decays. By combining an accurate determination of experimental effects with marked in situ constraints of theoretical inputs, we reach a precise measurement of the W mass, of 80 360.2 $\pm$ 9.9 MeV, in agreement with the standard model prediction.