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T: Fachverband Teilchenphysik

T 51: Flavour Physics III

T 51.9: Talk

Wednesday, March 18, 2026, 18:15–18:30, KH 01.011

Separation of different quantum states of B⁰ B⁰ meson pairs at the Upsilon 5S — •Celia Álvarez Álvarez, Kilian Brückner, Vanessa Geier, and Hans-Günther Moser — Max Planck Institut für Physik, Boltzmannstr. 8 85748 Garching.

At the Upsilon 5S the energy is high enough that B⁰ can be produced in excited states such as Υ(5S)→ B⁰B⁰, Υ(5S)→ B^0*B⁰+c.c. and Υ(5S)→ B^0*B^0*. The B^0* decays via the emission of a photon and B⁰/B⁰ pairs can be observed in different quantum states. Those pairs which stem from B⁰B⁰ and B^0*B^0* have a C=−1 antisymmetric wave function, while the ones that decay from B^0*B⁰+c.c. have a C=+1 symmetric wave function. The different states show different forms of entanglement.
Using data of the Belle experiment, these three decay modes are reconstructed through the three hadronic decay chains: B⁰ → D⁻ π⁺   with   D⁻ → K⁺ π⁻ π⁻ ,    B⁰ → D^*− π⁺   with   D^*− → D⁰ π_s⁻   and   D⁰ → K⁺ π⁻ or D⁰ → K⁺ π⁻ π⁺ π⁻. Using M_bc, the three decay modes are separated and signal and background is fitted using Δ E. Using the S-weight technique the Δ t signal is extracted and a signal fit is performed with the weighted data.

Keywords: Belle; Entanglement; Flavour physics; CP violation; Upsilon 5S