Measurement of the jet mass in hadronic decays of boosted W bosons at 13 TeV and extraction of the W boson mass

TL;DR

This paper measures the jet mass of boosted W bosons in proton-proton collisions at 13 TeV using CMS data, and extracts the W boson mass with unprecedented precision from all-jets final states.

Contribution

It presents the first unfolded double-differential cross section measurements of W+jets as a function of jet pT and soft-drop mass, leading to a precise W boson mass determination.

Findings

W boson mass measured as 80.83 ± 0.55 GeV

First all-jets W mass measurement with smallest uncertainty

Unfolded double-differential cross sections provided

Abstract

The jet mass of W bosons decaying to a quark-antiquark pair is measured in W+jets events from proton-proton collisions at a center-of-mass energy of 13 TeV. The data used were collected by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 138 fb$^{-1}$. Hadronic decays of W bosons with high momenta produce strongly collimated decay products due to the large Lorentz boost, and are reconstructed as single large-radius jets. These jets have a characteristic substructure that is exploited to distinguish them from the large background of quark- and gluon-initiated jets. The jet mass is computed using the soft-drop algorithm, which suppresses soft wide-angle radiation that leads to a broadening of the jet mass distribution. For the first time, unfolded measurements are presented of the double-differential W+jets cross section as a function of the jet transverse momentum and soft-drop mass. From these distributions, the W boson mass is obtained, with a value of 80.83 $\pm$ 0.55 GeV, achieving the smallest uncertainty available today from an all-jets final state at a hadron collider.