Discovery at the intensity frontier
Belle II is a particle-physics experiment featuring state-of-the-art detectors to study electron-positron collisions produced by the SuperKEKB collider in Japan. Belle II virtual tours here and here. Its chief mission is to discover the new fundamental particles that complete the Standard Model at high energy, or to set stringent constraints on their dynamics. This is achieved by studying heavy-quark and lepton transitions sensitive to dynamics at energies much higher than those directly probed at CERN's LHC. Belle II was built and is now operated by over 1160 scientists from 130 research institutions across 27 countries. Unique access to tau-lepton dynamics and unprecedented sensitivity to decays of B and D hadrons into neutral particles position Belle II at the forefront of the intensity frontier.
We are about six staff scientists and a growing crop of students and postdocs with a diverse background spanning from detector construction in NA1, DELPHI, ALEPH, CDF, and BaBar, to data analysis in CHARM, DELPHI, ALEPH, BaBar, CDF, CMS, and LHCb. Our Belle II activities develop along two main thrusts, detector development and construction, and physics data analysis.
The instrumentation effort currently focuses on the operation of diamond detectors for monitoring the radiation on the silicon vertex detector. We also built and operate other systems for monitoring other environmental parameters relevant for the vertex detector performance. The vertex detector surrounds almost hermetically the accelerator's interaction point and samples with high spatial precision the trajectories of the charged particles emerging from the collision. Precision tracking is essential for the science of Belle II, since charged particles are the most abundant decay products of tau leptons and bottom and charm mesons. With its 8+ million channels installed close to the beam, the vertex detector operates at the heart of Belle II in a high radiation environment that affects tracking performance. Monitoring the instantaneous radiation field in real time and the integrated doses is therefore critical. Trieste designed, built, characterized, tested, installed, and operates 28 single-crystal diamond sensors that monitor radiation and trigger appropriate measures should the conditions become unsafe for the detector. In addition, Trieste performed dedicated in-depth tests of silicon sensors prior to final installation at KEK.
The physics analysis effort is using Belle and Belle II data to produce high profile results in charmless B decays, semileptonic B decays and charm decays. Most of our analyses are sensitive to contributions from non-standard-model particles and offer improved insight into the fundamental parameters associated with the weak interactions of quarks. We also have significant physics leadership responsibilities. Mirco Dorigo is currently coordinating the B hadronic working group (50 collaborators). Diego Tonelli has been coordinating the B to charmless working group (30 collaborators) in 2019-2021 and the physics of the whole experiment in 2022-2023.