QCD Sum Rule Study of Topped Mesons Within Heavy Quark Effective Theory

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 (tq¯, with q¯=u¯,d¯,s¯). In contrast to the extensively studied toponium (tt¯) 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), topped mesons have a simpler quark composition and more favorable decay channels (a topped meson is anticipated to decay weakly into a Υ meson and a charmed meson), enhancing their potential for both theoretical analysis and experimental discovery.