A Precision Measurement of the Mass of the Top Quark

TL;DR

This paper presents a highly precise measurement of the top quark mass using an improved technique, significantly refining the value and implications for the Higgs boson mass predictions within the Standard Model.

Contribution

The paper introduces a novel method that extracts more information from each top-quark event, achieving a substantially improved precision in top mass measurement.

Findings

Top quark mass measured as 178.0 ± 4.3 GeV/c^2

Higgs mass likelihood increased to 117 GeV/c^2

Upper limit on Higgs mass raised to 251 GeV/c^2

Abstract

The Standard Model of particle physics contains about two dozen parameters - such as particle masses - whose origins are still unknown and cannot be predicted, but whose values are constrained through their interactions. In particular, the masses of the top (t) quark (M_t) and W boson constrain the mass of the long-hypothesized, but thus far not observed, Higgs boson. A precise measurement of the top-quark mass can therefore point to where to look for the Higgs, and indeed whether the hypothesis of a SM Higgs is consistent with experimental data. Since top quarks are produced in pairs and decay in only ~10^-24 s into various final states, reconstructing their mass from their decay products is very challenging. Here we report a technique that extracts far more information from each top-quark event and yields a greatly improved precision on the top mass of 5.3 GeV/c^2, compared to previous measurements. When our new result is combined with our published measurement in a complementary decay mode and with the only other measurements available, the new world average for M_t becomes 178.0 +- 4.3 GeV/c^2. As a result, the most likely Higgs mass increases from the experimentally excluded value of 96 GeV/c^2 to 117 GeV/c^2, which is beyond current experimental sensitivity. The upper limit on the Higgs mass at 95% confidence level is raised from 219 GeV/c^2 to 251 GeV/c^2.