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

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.

Figures (9)

• Figure 1: Feynman diagram for tree-level ${ \mathup{{{W}}{} _{ {}} ^{ {}}} }\xspace({ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{ \overline{ {{ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace')\text{+jets}$ production.
• Figure 2: Acceptance as a function of $m_\mathrm{SD}\xspace^\mathrm{ptcl}$ without (upper) and with (lower) the requirement $N_{2}^{(1)}\xspace<0.2$ at the particle level. The acceptance is calculated using the ${ \mathup{{{W}}{} _{ {}} ^{ {}}} }\xspace({ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{ \overline{ {{ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace')\text{+jets}$ signal simulation with 2018 detector conditions.
• Figure 3: Reconstructed $m_\mathrm{SD}$ distributions in the second $p_{\mathrm{T}}$ bin with $650 < p_{\mathrm{T}}\xspace < 725\,\text{Ge\spaceV}\xspace$ in the signal (upper row) and control (lower row) regions defined using the $N_{2}^{(1),\mathrm{DDT}}$ (upper) and $P^{\mathrm{PN, DDT}}_{\mathrm{W vs. QCD}}$ (lower) taggers after the background estimation and a fit to the data, explained in Section \ref{['sec:background']}. All four data-taking periods are combined, resulting in a total integrated luminosity of 138$\,\text{fb}^{-1}$. The lower panels show the data-to-simulation ratio. The error bars correspond to the statistical uncertainty in the data. The dashed band is the total uncertainty on the background after a fit to the data distribution.
• Figure 4: Residual function $r(\hat{p}_{\mathrm{T}}\xspace, \hat{\rho}_\mathrm{SD}\xspace)$ obtained from a fit to data, when using the $P^{\mathrm{PN, DDT}}_{\mathrm{W vs. QCD}}$ as jet tagger. The arguments of the function $r$, $\hat{p}_{\mathrm{T}}$ and $\hat{\rho}_\mathrm{SD}$ are functions of $m_\mathrm{SD}$ and $p_{\mathrm{T}}$ and correspond to the normalized observables $p_{\mathrm{T}}$ and $\rho_{\mathrm{SD}}$, scaled to lie in the interval $[0,1]$. The hatched area is excluded from the analyses by selecting $\rho_{\mathrm{SD}}\xspace < -2.1$.
• Figure 5: Summary of the effect of the systematic uncertainties in the reconstructed SD jet mass in the ${ \mathup{{{W}}{} _{ {}} ^{ {}}} }\xspace({ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{ \overline{ {{ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace')\text{+jets}$ signal sample in a representative $p_{\mathrm{T}}$ bin. The dominant shape effects can be attributed to uncertainties in the hadronization model, jet energy scale, and final-state shower. The jet energy scale and final state shower mainly affect the region of the $\mathup{{{W}}{} _{ {}} ^{ {}}}$ boson mass peak ($70<m_\mathrm{SD}\xspace<110\,\text{Ge\spaceV}\xspace$).