First Measurement of the W Boson Mass in Run II of the Tevatron

TL;DR

This is the most precise single measurement of the W-boson mass to date.

Abstract

We present a measurement of the W boson mass using 200/pb of data collected in pbar p collisions at sqrt(s) = 1.96 TeV by the CDF II detector at Run II of the Fermilab Tevatron. With a sample of 63964 W -> e nu candidates and 51128 W -> mu nu candidates, we measure M_W = (80413 +- 34 (stat) +- 34 (syst) = 80413 +- 48) MeV/c^2. This is the most precise single measurement of the W boson mass to date.

Figures (4)

• Figure 1: The $Z \rightarrow \mu \mu$ (top) and $Z \rightarrow ee$ (bottom) mass fits, showing the data (points) and the simulation (histogram). The arrows indicate the fitting range.
• Figure 2: The distribution of $E / pc$ for the $W \rightarrow e \nu$ data (points) and the best-fit simulation (histogram) including the small jet background (shaded). The arrows indicate the fitting range used for the electron energy calibration. The jet background, which is barely visible on this scale, contributes a negligible uncertainty in the calibrations of the electron energy scale and the amount of radiative material.
• Figure 3: Left: The $u_{||}$ distribution for the electron channel data (points) and simulation (histogram). Right: The $|\vec{u}|$ distribution for the muon channel. The mean and r.m.s. of the histograms agree between data and simulation, within the statistical precisions of $\approx 1$%.
• Figure 4: The $m_T$ distribution of the data (points) and the best-fit simulation template (histogram) including backgrounds (shaded), for muons (top) and electrons (bottom). The arrows indicate the fitting range. The $\chi^2$/dof for the electron channel distribution receives large contributions from a few bins near 65 GeV/$c^2$, which do not bias the mass fit.