History of Belle and some of its lesser known highlights

TL;DR

This paper reviews the early history of the Belle experiment, highlighting its key contributions to CP violation, charmonium production, scalar meson structure, and spin fragmentation, beyond its well-known role in testing the Kobayashi-Maskawa mechanism.

Contribution

It presents lesser-known significant results from Belle, including discoveries in charmonium production, meson structure, and spin physics, expanding understanding beyond CP violation studies.

Findings

Large cross sections for double charmonium production

Probes of low-mass scalar meson structure

First measurements of the Collins spin fragmentation function

Abstract

I report on the early history of Belle, which was almost entirely focused on testing the Kobayashi Maskawa mechanism for $CP$ violation that predicted large matter-antimatter asymmetries in certain $B$ meson decay modes. Results reported by both BaBar and Belle in the summer of 2001 verified the Kobayashi Maskawa idea and led to their Nobel prizes in 2008. In addition to studies of CP violation, Belle (and BaBar) reported a large number of important results on a wide variety of other subjects, many of which that had nothing to do with B mesons. In this talk I cover three (of many) subjects where Belle measurements have had a significant impact on specific sub-fields of hadron physics but are not generally well know. These include: the discovery of an anomalously large cross sections for double charmonium production in continuum e+e- annihilation; sensitive probes of the structure of the low-mass scalar mesons; and first measurements of the Collins spin fragmentation function.