Mainz 2022 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 63: Hadron Structure and Spectroscopy XI

HK 63.1: Gruppenbericht

Donnerstag, 31. März 2022, 14:00–14:30, HK-H8

The search for dibaryons in coherent photoproduction off the deuteron at the BGOOD experiment — •Thomas Jude for the BGOOD collaboration — Physikalisches Institut, Universität Bonn

The discovery of the d^*(2380) hexaquark, first identified in the fusion reaction pn→ dπ⁰π⁰ has sparked renewed interest in dibaryon searches in the non-strange sector. Evidence of the d^*(2380), with IJ^P = 03⁺, has been observed in a multitude of final states and observables. Conversely, recent models benefiting from high precision experimental data and theoretical developments have described the d^*(2380) via triangle singularity mechanisms.

The BGOOD experiment at ELSA provides a unique approach to measure such mechanisms via the coherent reaction, γ d → π⁰π⁰ d. The presented results are from a full kinematic reconstruction, with final state deuterons identified in the forward spectrometer and π⁰ electromagnetic decays in the central BGO Rugby Ball. The strength of the measured differential cross section exceeds what can be described by models of coherent photoproduction and instead is consistent with the three isoscalar dibaryon candidates reported by the ELPH collaboration at 2.38, 2.47 and 2.63 GeV/c². A low mass enhancement in the π⁰π⁰ invariant mass is also observed at the d^*(2380) centre-of-mass energy. At higher centre-of-mass energies, a narrow peak in the π⁰ d invariant mass at 2114 MeV/c² with a width of 20 MeV/c² supports a sequential two-dibaryon decay mechanism.

Supported by DFG projects 388979758/405882627 and the European Union*s Horizon 2020 programme, grant 824093.