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T: Fachverband Teilchenphysik

T 51: Flavour Physics III

T 51.7: Vortrag

Mittwoch, 18. März 2026, 17:45–18:00, KH 01.011

Event Selection for Υ(5S) Entanglement Studies — •Kilian Brückner, Hans-Günther Moser, Vanessa Geier, Louise Beriet, and Celia Álvarez — Max Planck Institut für Physik, Boltzmannstraße 8, 85748 Garching

The entanglement of B⁰B⁰ meson pairs from Υ(4S) decays is an important resource for many analyses, especially for time dependent CP violation analyses. At the Υ(5S), however, more features of the entanglement itself can be studied.
Due to the higher energy of the Υ(5S), excited B^0* mesons can be produced from its decay. These spin 1 excited B^0* states decay via the emission of a photon, so that C=+1 and C=−1 entangled B⁰B⁰ states are produced. In comparison, The Υ(4S) only provides a state entangled with a C=−1 wave function.
The challenge for an analysis at the Υ(5S) arises from the low amount of 121 fb⁻¹ of data, so far taken only by Belle. This requires an efficient event selection with many decay channels to keep statistics high enough.
In this talk, the full event selection for the analysis is described. This includes choosing the decay channels of the B mesons, as well as handling all occurring backgrounds. For the main background source of qq continuum, a gradient boosted decision tree is utilized.

Keywords: Belle; Belle II; TDCPV; Entanglement