A direct measurement of W boson decay width

TL;DR

This study directly measures the W boson total decay width $\Gamma_W$ from the $W\to e\nu$ transverse-mass spectrum in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV with the DØ detector. A detailed Monte Carlo model of $W$ production/decay, detector response, and backgrounds is fitted to the data using a binned likelihood approach across $90<m_T<200$ GeV, incorporating $\tau\nu$ and $Z\to ee$ backgrounds and PDF/production-model uncertainties. The extracted width is $\Gamma_W = 2.23^{+0.15}_{-0.14}({\rm stat})\;\mathrm{GeV}$ with a total systematic uncertainty of $\pm 0.10$ GeV, in good agreement with the Standard Model prediction $\Gamma_W \approx 2.0921$ GeV, and it provides a robust cross-check against indirect measurements. The analysis thoroughly quantifies uncertainties from electron energy scale/resolution, hadronic energy response, luminosity-related effects, background estimates, and PDFs, reinforcing the precision and reliability of a direct width determination.

Abstract

Based on 85 pb$^{-1}$ data of \ppbar collisions at $\sqrt{s}=1.8$ \tev\ collected using the DØdetector at Fermilab during the 1994-1995 run of the Tevatron, we present a direct measurement of the total decay width of the \wb\ boson, $Γ_W$. The width is determined from the transverse mass spectrum in the $W \to e+ν_e$ decay channel and found to be $Γ_W = 2.23^{+ 0.15}_{- 0.14}$(stat.)$\pm 0.10$(syst.)GeV, consistent with the expectation from the standard model.

Figures (6)

• Figure 1: Monte Carlo simulations of the transverse mass spectrum for different $W$ boson widths. The selections, $E_T(e) >$ 25 GeV and $E_T(\nu) >$ 25 GeV, are applied to MC sample. The circles show the spectrum for $\Gamma_W = 1.60$ GeV, the squares for $\Gamma_W = 2.10$ GeV, and triangles for $\Gamma_W = 2.60$ GeV. Distribution are normalized arbitrarily in the transverse mass region shown.
• Figure 2: Transverse mass distribution of $W \rightarrow e\nu$ event candidates.
• Figure 3: Invariant mass distribution of $Z\rightarrow e^{+}e^{-}$ events compared to Monte Carlo simulation. The histrogram is the MC and the black dot with error bar is the data. The $Z\rightarrow e^{+}e^{-}$ candidate require both electrons be in the CC.
• Figure 4: The transverse mass distribution for the multijet background. The line represents the results of the fit described in the text.
• Figure 5: Results of the log-likelihood fit of the data to Monte Carlo templates for different $\Gamma_W$.