Extraction of the Width of the W Boson from Measurements of sigma(ppbar->W+X)B(W->e nu) and sigma(ppbar->Z+X)B(Z->e e) and their Ratio

TL;DR

This work measures W and Z production in pp̄ collisions at 1.8 TeV via their electron decays, using the DØ detector to determine cross sections times branching fractions and their ratio. By combining W→eν and Z→ee channels and applying small theoretical corrections (Drell–Yan, NLO electroweak effects), the study extracts the W branching fraction and total width, and places a 95% CL limit on any invisible W decays. The analysis benefits from a large data sample and a careful treatment of acceptances, efficiencies, and backgrounds, with luminosity uncertainty dominating the absolute cross sections while largely canceling in the ratio. The results provide a precise test of the Standard Model W width and constrain new physics channels that could contribute to Γ_W^inv. A supplementary 630 GeV dataset corroborates the findings, underscoring the robustness of the approach.

Abstract

We report on measurements of inclusive cross sections times branching fractions into electrons for W and Z bosons produced in ppbar collisions at sqrts=1.8 TeV.From an integrated luminosity of 84.5 inverse pb recorded in 1994--1995 using the D0 detector at the Fermilab Tevatron, we determine sigma(ppbar->W+X)B(W->e nu) = 2310 +- 10(stat) +- 50(syst) +- 100(lum) pb and sigma(ppbar->Z+X)B(Z->e e) = 221 +- 3(stat) +- 4(syst) +- 10(lum) pb. From these, we derive their Ratio R = 10.43 +- 0.15(stat) +- 0.20(syst) +- 0.10(NLO), B(W->e nu) = 0.1066 +- 0.0015(stat) +- 0.0021(syst) +- 0.0011(theory)+- 0.0011(NLO), and Gamma_W = 2.130 +- 0.030(stat) +- 0.041(syst) +- 0.022(theory) +- 0.021(NLO) GeV. We use the latter to set a 95% confidence level upper limit on the partial decay width of the W boson into non-standard model final states, Gamma_W^{inv}, of 0.168 GeV. Combining these results with those from the 1992--1993 data gives R = 10.54 +- 0.24, Gamma_W = 2.107 +- 0.054 GeV, and a 95% C.L. upper limit on Gamma_W^{inv} of 0.132 GeV. Using a sample with a luminosity of 505 inverse nb taken at sqrts=630 GeV, we measure sigma(ppbar->W+X)B(W->e nu) = 658 +- 67 pb.

Figures (17)

• Figure 1: The vertex position calculated using the position of the electron cluster (as determined using the information from the third layer of the EM calorimeter) and the center-of-gravity of the electron track (as measured in the tracking chambers).
• Figure 2: The invariant mass distribution from the ee $Z\to ee$ candidate event sample. The shaded region represents the dielectron invariant mass requirement.
• Figure 3: (a) Frequency at which the standard vertex, $z_{\rm{standard}}$ (calculated using all tracks), is more than 10 cm away from the extrapolated track position, $z_e$, as a function of luminosity. For comparison, the frequency at which ee $Z\to ee$ events with two tight electrons have extrapolated track positions $z_1$ and $z_2$ differing by more than 10 cm is shown. (b) Invariant mass distribution for ee $Z\to ee$ events when the standard vertex position is used and when the electron vertex position is used.
• Figure 4: The transverse mass distribution from the eν $W\to e\nu$ candidate event sample.
• Figure 5: Invariant mass distribution for the CC-CC ee $Z\to ee$ data sample. A Breit-Wigner convoluted with a Gaussian resolution is fit to this distribution and the width is used to determine the constant term in the CC electron energy resolution. The $\chi^{2}$ per degree of freedom for the fit is 88.7/56.