QCD sum rule study of topped mesons within heavy quark effective theory

TL;DR

This paper uses QCD sum rules within heavy quark effective theory to predict the properties of topped mesons containing a single top quark, providing insights into nonperturbative QCD dynamics and potential experimental signatures.

Contribution

It introduces a novel nonperturbative study of topped mesons using QCD sum rules, predicting their masses and decay properties, complementing existing toponium analyses.

Findings

Predicted topped meson masses near 173.1 GeV

Topped mesons have longer lifetimes and narrower widths than toponium

Decay channels include weak decay into $U$ and charmed mesons

Abstract

Motivated by the recent CMS observation of a near-threshold enhancement in top quark pair production, we investigate a novel class of hadronic systems containing a single top quark: the topped mesons ($t\bar{q}$, with $\bar q = \bar u, \bar d, \bar s$). In contrast to the extensively studied toponium ($t\bar{t}$) system, analyzed primarily within perturbative QCD, topped mesons offer a complementary nonperturbative probe of QCD dynamics in the heavy quark limit. These states are expected to exhibit longer lifetimes and narrower decay widths than toponium, as only a single top quark undergoes weak decay. We employ QCD sum rules within the framework of heavy quark effective theory to study the structure and mass spectrum of ground-state topped mesons. Our analysis predicts masses near 173.1 GeV, approximately 0.5-0.6 GeV above the top quark pole mass. Compared with singly topped baryons ($tqq$, with $q = u, d, s$) studied concurrently in [arXiv:2507.05895], topped mesons have a simpler quark composition and more favorable decay channels (a topped meson is anticipated to decay weakly into a $\Upsilon$ meson and a charmed meson), enhancing their potential for both theoretical analysis and experimental discovery.