At the SuperKEKB accelerator in Tsukuba, Japan, electrons of about 7 gigaelectronvolts collide with positrons of about 4 gigaelectronvolts, producing pairs of bottom and antibottom quarks that decay into entangled B mesons. Because the pairs are entangled, measuring the state of one meson reveals information about the other without any direct interaction. The Belle II experiment has now amassed the world's largest sample of such pairs, surpassing its predecessor Belle.
The dataset matters because subtle differences between B mesons and their antiparticles bear on one of cosmology's deepest puzzles: why the universe contains far more matter than antimatter. Belle II's collisions have precisely known starting conditions and less background noise than those at the Large Hadron Collider, making them especially suited to decays involving invisible particles such as neutrinos, possible dark-matter candidates, and exotic multi-quark states.
LMU is embedded in the effort through Thomas Kuhr, Professor of Experimental Physics, and through the ORIGINS Cluster of Excellence, where the origin of the matter-antimatter asymmetry is an active research theme. With SuperKEKB already colliding particles at more than twice the rate of its predecessor, data taking is paused for maintenance and will resume next year, while a major upgrade of accelerator and detector is planned from 2032.