We propose a new algorithm for the identification of the production flavor of neutral D mesons in the Belle II experiment. The algorithm exploits the correlation between the flavor of a reconstructed neutral D meson (signal D meson) and the electric charges of particles reconstructed in the rest of the eþ e− → cc̄ event. These include those originating from the decay of the other charm hadron produced in the event, as well as those possibly produced in association with the signal D meson. We develop the algorithm using simulation and calibrate it in data using decay modes that identify the flavor of the decaying neutral D meson. We use a data sample of eþ e− collisions, corresponding to 362 fb−1 of integrated luminosity, collected by Belle II at center-of-mass energies near the ϒ(4S) mass. The effective tagging efficiency in data is (47.91± 0.07(stat) ± 0.51(syst))%, independent of the neutral-D-meson decay mode. This charm flavor tagger will approximately double the effective sample size of many CP-violation and charm-mixing measurements that so far have exclusively relied on neutral D mesons originating from D*± decays. While developed for Belle II, the basic principles underlying the charm flavor tagger can be used in other experiments, including those at hadron colliders.
Adachi, I., Aggarwal, L., Ahmed, H., Aihara, H., Akopov, N., Aloisio, A., et al. (2023). Novel method for the identification of the production flavor of neutral charmed mesons. PHYSICAL REVIEW D, 107(11), 112010-1-112010-15 [10.1103/PhysRevD.107.112010].