# Workpackage 1

Search for new physics signals at Belle II

Coordinator: prof. Christoph Schwanda (OEAW-HEPHY)

The search for new physics requires to perform precision measurements of a large variety of channels, which in turn requires excellent control of all detector performances. The two activities have to be developed in parallel and in close collaboration. For this reason, the task dedicated to detector performances is by far the largest one, as it is connected to all the others.

Determine and optimize detector resolutions and efficiencies using real data, in order to provide precise inputs to physics analyses. Each sub-detector has to be studied both by itself and in combination with the others, thus requiring the collaboration of all sub-detector experts from different groups.

Task 1.2: Study of CP violation and search for new phenomena in rare decays

Physics analyses to test CKM matrix unitarity (measurement of |Vcb| and |Vub| using leptonic and semileptonic decays; measurement of the angles of the CKM unitarity triangle, in particular the gamma angle), studies of rare B decays (B→Xs gamma; charmless hadronic B decays) and of rare charm decays are developed in this task.

Task 1.3: Lepton flavour and lepton universality violations

Hints for lepton flavour non-universality are currently seen in the B → D* tau nu and B → Xs l+l- channels by the BaBar, Belle and LHCb experiments. These anomalies can be interpreted within various new physics models but require final experimental confirmation, for which Belle II measurements are essential. Lepton flavour violation is best tested in tau decays, where many channels can also be studied. Missing energy due to neutrinos requires in turn full event reconstruction to reject backgrounds.

Task 1.4: Dark sector and exotics

Production of the so called “dark photon” and of other Z-like or Higgs-like particles will be searched for. Limits on exotic processes including axions and WIMPS can also be improved. All such events require hermeticity and excellent control of machine and accidental backgrounds.