Measurement of the $W$ boson mass with the D0 detector

TL;DR

The study presents a precise determination of the $W$ boson mass $M_W$ using 4.3 fb$^{-1}$ of D0 Run IIb data, calibrated against $Z o ee$ events and employing a fast Monte Carlo that reproduces detector response and recoil correlations. The analysis uses three complementary observables, $m_T$, $p_T^e$, and ${ ot ext{E}}_T$, with template fits and a blinded approach to avoid bias, achieving a Run IIb result of $M_W = 80.367 \,\pm\ 0.026$ GeV when combined with the prior Run IIa measurement to yield $M_W = 80.375 \,\pm\ 0.023$ GeV. A comprehensive treatment of systematics—electronic energy scale, recoil modeling, PDFs, EW corrections, and detector material—drives the precision, with Z calibration and a meticulous material-tuning strategy playing a central role in controlling non-linearities in the electron energy response. The results are consistent with the Standard Model, with implications for electroweak fits in the Higgs boson mass regime and cross-experiment consistency with CDF and LEP measurements. The methodological framework—data-driven calibration, fast-template MC, and BLUE combination—provides a robust blueprint for high-precision EW measurements in hadron-collider environments.

Abstract

We give a detailed description of the measurement of the $W$ boson mass, $M_W$, performed on an integrated luminosity of 4.3 fb$^{-1}$, which is based on similar techniques as used for our previous measurement done on an independent data set of 1 fb$^{-1}$ of data. The data were collected using the D0 detector at the Fermilab Tevatron Collider. This data set yields $1.68\times 10^6$ $W\rightarrow eν$ candidate events. We measure the mass using the transverse mass, electron transverse momentum, and missing transverse energy distributions. The $M_W$ measurements using the transverse mass and the electron transverse momentum distributions are the most precise of these three and are combined to give $M_W$ = 80.367 $\pm$ 0.013 (stat) $\pm$ 0.022 (syst) GeV = 80.367 $\pm$ 0.026 GeV. When combined with our earlier measurement on 1 fb$^{-1}$ of data, we obtain $M_W$ = 80.375 $\pm$ 0.023 GeV.

Figures (61)

• Figure 1: [color online] The (a) $p_{T}^{e}$ and (b) $m_T$ spectra for simulated $W$ bosons without detector resolution effects and $W$ boson transverse momentum $p_{T}^{W}=0$ (solid line), with the natural $p_{T}^{W}$ spectrum at the Tevatron (shaded area), and with the natural $p_{T}^{W}$ distribution and all detector resolution effects included (points). All curves are normalized to unit area.
• Figure 2: [color online] (a) Definition of $\eta$ and $\xi$ axes for $Z \rightarrow ee$ events. (b) Definition of $u_{\parallel}$ and $u_{\perp}$. The variable $u_{\parallel}$ is negative when opposite to the electron direction.
• Figure 3: Side view of one quadrant of the D0 detector, not showing the muon subdetector system. The calorimeter segmentation and tower definition are shown in both CC and EC. The lines extending from the center of the calorimeter denote the pseudorapidity ($\eta_{\rm det}$) coverage of cells and projected towers. The solenoid and tracking detectors are shown in the inner part of the detector.
• Figure 4: [color online] Instantaneous luminosity profiles for Run IIa and Run IIb. The instantaneous luminosity is given as a multiple of $36\times 10^{30}\,\text{cm}^{-2}s^{-1}$ since there were 36 $p\bar{p}$ bunch crossings per turn in the Tevatron Collider.
• Figure 5: The 13 calorimeter towers defined as the electron reconstruction cone. The cone is centered on the tower with the highest transverse energy. A circle of radius $\Delta R=0.2$ is shown for comparison.