Toponium: the smallest bound state and simplest hadron in quantum mechanics

TL;DR

This paper investigates toponium, the smallest quantum bound state of a top quark and its antiparticle, revealing its potential to probe quantum chromodynamics and enabling highly precise top quark mass measurements.

Contribution

It introduces the first experimental evidence of toponium and demonstrates its use for precise top quark mass determination with reduced uncertainties.

Findings

Toponium signal exceeds 5σ significance in collider data.

Top quark mass can be measured with ten times less uncertainty.

Method reduces systematic uncertainties by at least 2.7 times.

Abstract

We explore toponium, the smallest known quantum bound state of a top quark and its antiparticle, bound by the strong force. With a Bohr radius of $8\times 10^{-18}$~m and a lifetime of $2.5 \times 10^{-25}$~s, toponium uniquely probes microphysics. Unlike all other hadrons, it is governed by ultraviolet freedom. This distinction offers novel insights into quantum chromodynamics. Our analysis reveals a toponium signal exceeding $5\sigma$ in the distribution of the cross section ratio between $e^+e^- \rightarrow b\bar{b}$ and $e^+e^- \rightarrow q\bar{q}$ ($q=b,c,s,d,u$), based on 400~fb$^{-1}$ of data collected at $\sqrt{s}\approx 341~{\rm GeV}$. This discovery enables a top quark mass measurement with an uncertainty reduced by a factor of ten compared to current precision levels. Moreover, this method improves the systematic uncertainty by at least a factor of 2.7 compared to any other possible methods.