Belle II

Introduction of Belle II experiment

The Belle II experiment, the successor to the Belle experiment, is a particle physics experiment located at the KEK (高エネルギー加速器研究機構, High Energy Accelerator Research Organization) in Tsukuba, Japan. Operating at the SuperKEKB electron ( )-positron ( ) collider, Belle II is designed to explore the fundamental physics of heavy-flavour particles, investigate the matter-antimatter asymmetry in the universe, and search for physics beyond the Standard Model.

Background and Scientific Motivation

While the Standard Model has been remarkably successful in describing the fundamental particles and their interactions, it remains incomplete. For instance, it cannot fully account for the observed abundance of matter over antimatter in the universe, nor does it provide candidates for dark matter.

To address these open-ended questions, the SuperKEKB is designed to be a "B-factory"—a facility capable of producing vast quantities of  mesons. The center-of-mass (c.m.) energy of its /  beams is around the Upsilon(4S) particle, which mainly decays to a pair of B mesons promptly. With the nano-beam technology and high beam currents, the design peak luminosity is roughly 30 times higher than its predecessor, KEKB. At that c.m. energy, the SupereKEKB also works as a Charm-factory and tau-factory by producing roughly equal amount of  mesons and  leptons.

The Belle II detector is a nearly hermetic detector around the /  interaction point to collect the signals of various collision events. The Belle II is the successor of Belle experiment, which, together with BaBar experiment, was commissioning in the first decade of 21th century and led to the 2008 Nobel prize in physics by verification of the Kobayashi-Maskawa theory in Charge-Parity (CP) violation, one possible explanation related to the matter-antimatter asymmetry.

With high luminosity commissioning, Belle II aims to collect an unprecedented integrated luminosity of 50 , about 50 times of what KEKB/Belle had achieved. By conducting precision measurements of rare decays, CP violation, and flavor-changing processes, Belle II searches for subtle deviations from Standard Model predictions.

Belle II acts as an indispensable complement to energy-frontier experiments like those at CERN's Large Hadron Collider (LHC). While high-energy colliders search for new heavy particles directly, Belle II explores new physics through precise intensity-frontier measurements of rare interactions.

NTUHEP at Belle II

NTU High Energy Physics group had joined the Belle experiment and made major contributions to the detector R&D and construction, as well as physics outputs. To continue our contribution to the new generation B-factory, we have participated in the Belle II experiment since the beginning. Our major achievements are the following.

.  BEAST2: beam background estimation

.  ECL simulation

.  CDC FE production

.  Belle II trigger system

.  ECL standalone neutral hadron identification

Current physics focus at NTUHEP.