Summary of Topical Group on Hadron Spectroscopy (RF07) Rare Processes and Precision Frontier of Snowmass 2021

TL;DR

This paper reviews recent advances in hadron spectroscopy, highlighting new exotic states, experimental efforts at major colliders, and theoretical approaches including phenomenology and lattice QCD, to better understand complex hadronic structures.

Contribution

It provides a comprehensive summary of experimental and theoretical progress in hadron spectroscopy, emphasizing new discoveries and ongoing challenges in interpreting multiquark states.

Findings

Discovery of numerous exotic hadrons like tetraquarks and pentaquarks.

Progress in experimental programs at LHCb, Belle II, BESIII, and future facilities.

Advances in theoretical models, reaction amplitude analysis, and lattice QCD simulations.

Abstract

Hadron spectroscopy, the driving force of high-energy physics in its early decades, has experienced a renaissance in interest over the past 20 years due to the discovery of scores of new, potentially "exotic states" (tetraquarks, pentaquarks, hybrid mesons, glueballs), as well as the observation of many new "conventional" hadrons. The new discoveries expose our lack of understanding about hadronic states, beyond just a few low excitations of the simplest quark configurations. Even so, no single theoretical interpretation (such as hadron molecules, threshold effects, diquark compounds, or others) as yet successfully accommodates all of the new multiquark particles, while a great deal of work remains to extract signals of hybrids and glueballs from reaction-amplitude data. This document summarizes the current state of the field from both experimental and theoretical perspectives. On the experimental side, this report summarizes the current, planned, and proposed activities of LHCb and other LHC experiments, Belle II, BESIII, and GlueX, as well as the approved Electron-Ion Collider, the proposed Super Tau-Charm factory, and other future experiments. The theoretical portion provides a brief overview of multiple phenomenological approaches studied to date, progress in rigorous studies of reaction amplitudes, and advances in lattice-QCD simulations.