Entanglement studies with Belle 𝚼(𝟓𝐒) Monte Carlo data (Masterkolloquium)

by Vanessa Geier (Friedrich-Alexander-Universität Erlangen-Nürnberg)

Wednesday Dec 10, 2025, 2:30 PM → 3:30 PM Europe/Berlin

A.1.29 - Caucasus (MPP)

In this work, we study the entanglement of the B mesons produced in Υ(5S) decays into the final states each with C = ±1 eigenvalue
Υ(5S) → B⁰ B⁰ (C = −1), 

Υ(5S) → B⁰ B^0∗ + c.c. (C = +1),

Υ(5S) → B^0∗ B^0∗ (C = −1).
For this purpose, we use Belle Monte Carlo data. The B mesons are reconstructed from hadronic decays:
B⁰ → D⁻π⁺, with D⁻ → K⁺π⁻π⁻     

B⁰ → D^∗−π⁺, with D^∗− → D⁰π⁻and ¯D⁰ → K⁺π⁻

B⁰ → D^∗−π⁺, with D^∗− → D⁰π⁻ and D⁰ → K⁺π⁻π⁺π⁻ .
We then determine the decay–time difference of the B meson pairs to investigate the time dependence of their quantum entanglement. Since an entanglement analysis has never been performed for Υ(5S) decays, this thesis establishes the foundation for such a study. This includes deriving the theoretical framework of entanglement at the Υ(5S), performing the necessary kinematic considerations for the decaytime calculation, and developing new time and flavor variables for the analysis, since the Belle II software framework is only partially applicable to the Υ(5S)) case. In addition, we generate Signal Monte Carlo samples of 1·10⁶ B0^(∗) B0^(∗) events to increase statistical precision. In the Υ(5S) system, it is possible to obtain two different types of entanglement. When these two types are mixed, one obtains a disentangled state, with the degree of disentanglement being equal to the mixing ratio of the two entangled states. By applying the model of partial spontaneous  disentanglement (PSD), which introduces a fraction ζ, we can measure this disentanglement fraction when mixing the states and thereby validate the theoretical prediction. To achieve this, we implemented the PSD framework for the Υ(5S) case. We verified that, when mixing the two entangled states in equal proportions, the expected disentanglement fraction of 100% is successfully reproduced.