Speaker: Diego Tonelli (INFN) – Title: First measurement of decay-time-dependent CP violation in B0->pi0pi0 decays
September 1 @ 4:00 pm - 5:00 pm
Research Progress Meeting
Date: September 1, 2026
Time: 4:00- 5:00 pm
Location: Sessler Conference Room- 50A-5132 [In-Person and HYBRID]
Speaker: Diego Tonelli (INFN)
Title: First measurement of decay-time-dependent CP violation in B0->pi0pi0 decays
Abstract: The Belle II experiment at the SuperKEKB e+e- collider is pushing the intensity frontier with unprecedented instantaneous luminosities. With the world’s largest Y(4S) data set, the experiment combines abundant data, advanced detector performance, and novel analysis methods to open new opportunities to advance quark-flavor physics. I report the first measurement of mixing-induced charge-parity (CP) violation in B^0 \to \pi^0 \pi^0 decays, a critical input for constraining the quark-mixing angle \phi_2 ( or \alpha). While traditionally deemed impossible without an order of magnitude more data, this measurement is achieved using a novel technique enabled by the SuperKEKB large-crossing angle, small interaction region and the Belle II pixel detector’s vertex resolution. By exploiting the quantum entanglement of the B^0B^0-bar pair from \Upsilon(4S) decays, the method uses only the companion B decay time to infer the signal CP parity.
Using 170 signal events reconstructed from a 0.4 ab^-1 sample, we determine the mixing-induced CP asymmetry, significantly improving \phi_2 constraints from B \to \pi \pi\ decays. This technique unlocks future time-dependent CP-violation measurements for final states without reconstructible decay vertices.
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