The W mass and width measurement challenge at FCC-ee
Paolo Azzurri
备注：
Submitted to EPJ+ special issue: A future Higgs and Electroweak factory (FCC): Challenges towards discovery, Focus on FCC-ee. arXiv admin note: text overlap with arXiv:1703.01626
The FCC-ee physics program will deliver two complementary top-notch precision determinations of the W boson mass, and width. The first and main measurement relies on the rapid rise of the W-pair production cross section near its kinematic threshold. This method is extremely simple and clean, involving only the selection and counting of events, in all different decay channels. An optimal threshold-scan strategy with a total integrated luminosity of $12\,{\rm ab}^{-1}$ shared on energy points between 157 and 163 GeV will provide a statistical uncertainty on the W mass of 0.5 MeV and on the W width of 1.2 MeV. For these measurements, the goal of keeping the impact of systematic uncertainties below the statistical precision will be demanding, but feasible. The second method exploits the W-pair final state reconstruction and kinematic fit, making use of events with either four jets or two jets, one lepton and missing energy. The projected statistical precision of the second method is similar to the first method's, with uncertainties of $\sim 0.5$ ($1$) MeV for the W mass (width), employing W-pair data collected at the production threshold and at 240-365 GeV. For the kinematic reconstruction method, the final impact of systematic uncertainties is currently less clear, in particular uncertainties connected to the modelling of the W hadronic decays. The use and interplay of Z$γ$ and ZZ events, reconstructed and fitted with the same techniques as the WW events, will be important for the extraction of W mass measurements with data at the higher 240 and 365 GeV energies.
Toward a Measurement of the Higgs Boson Mass with Natural-Width Precision at FCC-ee
Massachusetts Institute of Technology（麻省理工学院）；Brookhaven National Laboratory（布鲁克海文国家实验室）；Laboratoire AstroParticule et Cosmologie, CNRS/IN2P3（天体粒子与宇宙学实验室，法国国家科学研究中心/法国国家原子核及粒子物理研究所）；CERN（欧洲核子研究组织）
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