Erlangen 2026 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 51: Flavour Physics III

T 51.8: Vortrag

Mittwoch, 18. März 2026, 18:00–18:15, KH 01.011

Entanglement studies with Belle Υ(5S) data — •Louise Beriet, Vanessa Geier, and Hans-Günther Moser — Max Planck Institute for Physics, Garching, Germany

Compared to the Υ(4S), the Υ(5S) can decay into excited B^0*, giving rise to B⁰/B⁰ pairs in different quantum states. Directly after the Υ(5S) decay, the produced B^0(*)B^0(*) pairs are expected to be in a J^PC = 1^– state. Following the radiative transition B^0* → B⁰ γ, the system evolves into states with J^PC = 1⁻⁺. Depending on the C-parity, the B⁰/B⁰ can be in a symmetric (triplet) or antisymmetric (singlet) wave function, leading to different time evolutions of the entangled states. By mixing the two C-parity states C = −1 and C = +1, one can create a mixed state that is physically indistinguishable from a disentangled system.

We aim to study these effects using the Υ(5S) data available from Belle. The analysis includes the reconstruction of the signal B^0(*) meson pairs through the decay chain B⁰ → D⁻(→ K⁺ π⁻π⁻)π⁺, as well as obtaining the vertex and flavor information of the other B-meson inclusively. In addition, the B⁰/B⁰ quantum states are separated using the variables M_bc and Δ E.

We analyze the quantum coherence using the Partial Spontaneous Disentanglement model, which quantifies the entanglement via a number ζ ∈[0,1]. This parameter can be extracted by performing a likelihood fit on time-dependent parameters, which themselves can be computed from the spatial separation of the B⁰ pair. First results using Monte Carlo data are presented.

Keywords: Entanglement; Belle; B-Physics; Quantum