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arXiv · 2412.11254

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

Jing-Hang Fu·Yu-Ji Li·Hui-Min Yang·Yu-Bo Li·Yu-Jie Zhang·Cheng-Ping Shen
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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 $5σ$ 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.

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Jing-Hang Fu, Yu-Ji Li, Hui-Min Yang, Yu-Bo Li, Yu-Jie Zhang, Cheng-Ping Shen. 2025-05-28. Toponium: the smallest bound state and simplest hadron in quantum mechanics. https://doi.org/10.1103/fqc9-k315

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