On June 4, 2026, the Belle II experiment achieved a major milestone by surpassing the Υ (4S) resonance dataset collected by its predecessor, the Belle experiment. The integrated luminosity, which quantifies the total accumulated data, reached 757 fb⁻¹, exceeding Belle's record of 711 fb⁻¹.

This record-breaking achievement was made possible by improvements in both the luminosity of the SuperKEKB accelerator and the performance of the Belle II detector. Until recently, SuperKEKB faced several challenges, including Sudden Beam Loss (SBL), which made it difficult to increase the beam current. Through extensive investigations, the causes of these issues have been identified and better understood, enabling stable operation since late 2025. Students and staff from N Lab have made important contributions to this achievement through the operation and maintenance of the TOP counter photodetector system in the Belle II experiment, as well as the operation of beam-loss monitors and the development of beam-position monitoring systems for SuperKEKB.

See the official article for more details.

Celebration of the world's largest Υ(4S) data sample achieved by SuperKEKB and the Belle II detector, at the Electron-Positron Accelerator Control Building

*1 An electron–positron collision experiment conducted at the SuperKEKB accelerator at the High Energy Accelerator Research Organization（KEK）in Tsukuba, Ibaraki, Japan

*2 A phenomenon known as Sudden Beam Loss (SBL), in which the beam is lost within a few turns around the accelerator