Measurement of the W Boson Mass with the Collider Detector at Fermilab

TL;DR

This study delivers a precise direct measurement of the W boson mass using W→eν and W→μν decays from CDF Run IB data, employing in situ calibrations anchored by Z boson decays and a data-driven recoil model. The analysis meticulously calibrates lepton energy/momentum scales, models the W pT and detector recoil, and extracts Mw from the MTW spectrum with comprehensive systematic studies, dominated by Z-statistics and radiative corrections. The resulting Mw values for the electron and muon channels are combined to Mw = 80.470 ± 0.089 GeV/c^2, and when merged with Run IA results, Mw = 80.433 ± 0.079 GeV/c^2, aligning well with Standard Model expectations and informing electroweak fits and Higgs mass constraints. The work highlights the critical role of recoil modeling, parton distributions, and radiative effects in precision W-mass measurements at hadron colliders.

Abstract

We present a measurement of the W boson mass using data collected with the CDF detector during the 1994-95 collider run at the Fermilab Tevatron. A fit to the transverse mass spectrum of a sample of 30,115 W -> enu events recorded in an integrated luminosity of 84 pb^(-1) gives a mass Mw = 80.473 +- 0.065(stat.) +- 0.092(syst.) GeV/c^2. A fit to the transverse mass spectrum of a sample of 14,740 W -> munu events from 80 pb^(-1) gives a mass Mw = 80.465 +- 0.100(stat.) +- 0.103(syst.) GeV/c^2. The dominant contributions to the systematic uncertainties are the uncertainties in the electron energy scale and the muon momentum scale, 0.075 GeV/c^2 and 0.085 GeV/c^2, respectively. The combined value for the electron and muon channel is Mw = 80.470 +- 0.089 GeV/c^2. When combined with previously published CDF measurements, we obtain Mw = 80.433 +- 0.079 GeV/c^2.

Figures (56)

• Figure 1: One quarter of the CDF detector. The detector is symmetric about the interaction point. CDF uses a cylindrical coordinate system with the $z$ (longitudinal) axis along the proton beam axis; $r$ is the transverse coordinate, and $\phi$ is the azimuthal angle. Pseudorapidity ($\eta$) is defined as $\eta\equiv-{\rm ln(tan}(\theta/2))$, where $\theta$ is the polar angle relative to the proton-beam direction.
• Figure 2: Kinematics of $W$ boson production and decay for the events used in this analysis, as viewed in the plane transverse to the antiproton-proton beams. The recoil energy vector ${\bf u}$ is the sum of the transverse energy vectors $\bf E_T^i$ of the particles recoiling against the $W$. Although energy is a scalar quantity, "transverse energy" commonly denotes the transverse component of the vector whose $magnitude$ is the energy of the particle and $direction$ is parallel to the momentum of the particle.
• Figure 3: Variation of the average magnetic field as a function of run number. The left side of the plot corresponds to January 1994 and the right side of the plot to July 1995.
• Figure 4: The radial (R) distributions for conversions (solid line) and background (dashed line) for the Run IA inclusive electron sample. R is negative when the photon momentum direction is opposite to the vector from the beam spot to the conversion position due to the detector resolution.
• Figure 5: Reconstructed photon conversion vertex density in the $r-\phi$ plane for the innermost superlayer in the CTC, folded into 1/30 of the circumference (this layer has 30-fold symmetry). Each point represents one reconstructed vertex.