Colloquium: Spectroscopy of Hadrons at the COMPASS and Belle (II) Experiments

by Dr Stefan Wallner (Max Planck Institute for Physics, Garching)

Thursday 11 Jun 2026, 10:00 → 11:00 Europe/Vienna

Besprechungsraum 3A 1/2 (Marietta Blau Institute for Particle Physics, Dominikanerbastei 16 [PSK], 1010 Vienna)

Quark confinement in hadrons is a well-established phenomenon. However, a complete quantitative understanding of the principles governing the quark configurations realized in nature remains elusive. To address this, we study the excitation spectra of baryons and mesons, including searches for exotic states that defy the rules of the quark model. We present results from the Belle and Belle II experiments, utilizing the world’s largest dataset of e+e− collisions recorded at and around the Υ(nS ) resonances. We report on heavy-meson decays, the first search for exotic pentaquarks in inclusive Υ(1S ,2S ) decays, and precision studies of light mesons in τ-lepton decays.

Complementary, we discuss the strange-meson spectrum studied at the COMPASS experiment via diffractive scattering of a high-energy kaon beam. A partial-wave analysis of the K−π−π+ final state yields precision measurements of a broad spectrum of strange mesons and identifies a candidate for an exotic strange meson.