It has long been hypothesized that radiative decays of the charmonium-state J/psi, a gluon-rich process, are an ideal hunting ground for the glueball. The Beijing Spectrometer (BESIII) experiment gathered data for a total of ten billion J/psi decays in electron-positron annihilation – an unprecedented dataset to search for glueballs. In the first reporting period, we have analysed the huge dataset and identified several radiative decays J/psi, separating them from a large number of background processes. In close collaboration with theoretical physicists in the field of hadron spectroscopy, we have extended a computational framework that allows us to fit the complex amplitudes that theoretically describe the various decay mechanisms directly to the data in a coupled channel amplitude analysis. Due to the immense size of the dataset, the code is highly parallelized and developed such that calculations can also be performed on fast, modern graphics processing units (GPUs).
As part of the work on this project, a first test of our code with a direct application to the search for exotic hadrons containing bottom anti-bottom quark pairs has been published in Physical Review D, demonstrating both the viability of the approach, its potential in searches for exotic hadrons, and the general importance of a sound theoretical framework including coupled channel effects. Many properties of highly excited bottomonium states, among them a potential hybrid meson candidate, were determined for the first time, significantly extending our knowledge of the bottomonium-system. In the second funding period, we have performed coupled channel analyses of the radiative J/psi decays and of hadronic chi_cJ decays, with the aim to identify a glueball candidate and to search for a potential isovector partner-state to the f0(1710), the a0(1710) recently claimed in multiple works. While we find strong f0(1710) production in the gluon-rich J/psi decays, the a0(1710) is not confirmed in the highly precise study of chi_cJ decays, rendering the f0(1710) a likely candidate to largely overlap with the ground-state glueball. Both results will be published in timely fashion.
In total, results have been disseminated in 16 published articles, and through presentations at ten workshops or scientific conferences.
Furthermore, in collaboration with a German high school we have prepared a project in which students work directly with experimental data from the BESIII experiment, learning concepts of particle physics and data analysis, and directly applying them to our data. This project is continued and expanded with high school interns at the JGU Mainz.
