[Paper Review] Measuring the W Boson Mass at Hadron Colliders

U. Baur|ArXiv.org|Apr 28, 2003

Particle physics theoretical and experimental studies17 references3 citations

TL;DR

This paper evaluates techniques for measuring the W boson mass at hadron colliders, focusing on the Tevatron's Run II and the LHC. It compares transverse mass fitting and ratio methods, projecting a 30 MeV precision per experiment at the Tevatron and 15 MeV at the LHC, enabling indirect Higgs boson mass determination via electroweak radiative corrections.

ABSTRACT

We discuss the prospects for measuring the W mass in Run II of the Tevatron and at the LHC. The basic techniques used to measure M_W are described and the statistical, theoretical and detector-related uncertainties are discussed in detail.

Motivation & Objective

• To assess the feasibility and precision of W boson mass measurements at the Tevatron during Run II and at the LHC.
• To evaluate the statistical, theoretical, and detector-related uncertainties affecting $M_W$ determination.
• To compare the performance of traditional $M_T$ fitting with alternative methods like the $W/Z$ transverse mass ratio for improved systematics.
• To project the achievable precision in $M_W$ measurement under various luminosity scenarios, including Run IIb and LHC data sets.
• To support indirect Higgs boson mass determination through precision electroweak corrections using $M_W$

Proposed method

• Uses the transverse mass $M_T = \sqrt{2 p_T(\ell) p_T(\nu) (1 - \cos \phi_{\ell,\nu})}$ as the primary observable to measure $M_W$, minimizing sensitivity to $p_T^W$.
• Employs $M_T$ distribution fitting to extract $M_W$, with systematic uncertainties from detector resolution, $p_T^W$ modeling, and energy scale calibration.
• Applies the $W/Z$ transverse mass ratio method to cancel common scale uncertainties, directly measuring $M_W/M_Z$.
• Uses $Z \to \ell\ell$ data to calibrate recoil energy and resolution, reducing detector-related systematics.
• Projects uncertainties using extrapolated Run I data and Monte Carlo simulations for Run II and LHC luminosities.
• Considers the impact of $p_T^W$ smearing and detector resolution on $M_T$ and $p_T(\ell)$ distributions, favoring $M_T$ for stability.

Experimental results

Research questions

• RQ1 What is the projected precision of $M_W$ measurement at the Tevatron in Run II using the $M_T$ fitting method?
• RQ2 How do detector-related and theoretical uncertainties affect the $M_W$ measurement, and can they be mitigated?
• RQ3 Can the $W/Z$ transverse mass ratio method outperform traditional $M_T$ fitting at high luminosities?
• RQ4 What luminosity levels are required for systematic uncertainties to dominate over statistical ones in $M_W$ measurements?
• RQ5 What precision in $M_W$ is achievable at the LHC, and can it enable indirect Higgs boson mass determination?

Key findings

• A $W$ boson mass precision of $\pm 30$ MeV per experiment is projected for Run II of the Tevatron, based on statistical and systematic uncertainties.
• For 15 fb$^{-1}$ of integrated luminosity, the total uncertainty is expected to reduce to $\pm 17$ MeV, with systematic errors becoming dominant.
• At the LHC with 10 fb$^{-1}$, a statistical uncertainty below 2 MeV is expected, and a total uncertainty of $\pm 15$ MeV is achievable with 0.02% lepton energy scale precision.
• The $W/Z$ transverse mass ratio method reduces systematic uncertainty significantly—projected at 3 MeV for 30 fb$^{-1}$—compared to 15 MeV for the $M_T$ fit.
• For luminosities above 15 fb$^{-1}$, the ratio method yields a smaller total uncertainty ($\pm 11$ MeV) than the $M_T$ fit ($\pm 16$ MeV), making it superior in high-luminosity environments.
• The DØ Run Ib proof-of-principle analysis shows the ratio method yields $M_W = 80.115 \pm 0.211~{\rm (stat.)} \pm 0.050~{\rm (syst.)}$ GeV, confirming its reduced systematics despite larger statistical errors.