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Kazuki Kojima reported Belle II research results at Lepton Photon 2023

Kazuki Kojima presented Belle II research results at the 31st International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon 2023) held in Melbourne, Australia, from July 17th to 21st. The presentation slides can be found at the following link.

In his report, he presented the first result of R(D*) measurement from the Belle II experiment, to which he made a major contribution. The experimental average of the R(D)-R(D*) values had been found to deviate from the Standard Model (SM) prediction by more than 3σ. This discrepancy could induce a violation of lepton flavor universality, indicating the existence of New Physics beyond the SM, and new measurements are required for further tests. Even with the new Belle II result in the average, the deviation is still observed to exceed 3σ. Please refer to the Heavy Flavor Average Group page for the latest world average of R(D)-R(D*).

His comments are given below.

The R(D*) measurement addresses one of long-standing deviations from the Standard Model predictions, and it is significant for a New Physics searches. We are very pleased to have published the first measurement result from the Belle II experiment. At the same time, I am relieved because we faced many difficulties in the analysis, such as the control of background events and the evaluation of systematic uncertainties, which lasted until just before this Lepton Photon conference. In the future, our experiments will test R(D(*)) more precisely through analyses including further developments with dramatically increased data from Belle II.