|Fig.1 A picture of BGOegg inside the thermostatic booth (Left) and the drawings of BGOegg (Right).|
The origin of hadron mass is being studied by searching for mesic nuclei. We are particularly interested in the η' meson, whose mass is distictively larger than the other pseudoscalar meson masses due to the UA(1) anomaly. It is expected that the partial restoration of the chiral symmetry breaking, which may strongly affect the UA(1) anomaly, reduces the η' mass by 80-150 MeV at the nuclear density in the theoretical calculations based on the Nambu-Jona-Lasinio (NJL) model and the linear sigma model. The LEPS2/BGOegg experiments measure the momentum of an extremely forward proton by the time-of-flight and remove the large amout of backgrounds by the EM calorimeter.
We also aim to investigate a variety of hadron pictures through resonance studies. In the combination with the 0.6-1.3 GeV bremsstrahlung photon beam available at the booster synchrotron ring of ELPH, we can cover the wide range of photon beam energies continuously. For example, excited nucleon resonances are searched for by the total cross section measurements of the η, η', ω, π0π0, π0η photoproduction. The spin observables with the linearly polarized photon beam must help to clarify the resonance natures.
|Fig.2 The detector setup of the LEPS2/BGOegg experiments.|
The LEPS2/BGOegg experiments are carried out under the collaboration of ELPH (Tohoku University), RCNP (Osaka University), Kyoto University, KEK, RIKEN, JASRI (SPring-8), and several other institutes in the world. ELPH and RCNP cooperate the LEPS2 facility.
|2012||Dec||The EM calorimeter BGOegg was transferred to the LEPS2 experimental building at SPring-8|
|after the completion of its construction at ELPH.|
|2013||Jan||The construction of the LEPS2 beamline was completed.|
|The first photon beam was observed at the new beamline.|
|2013||Dec||Test data was taken after the preparations of individual detectors and DAQ.|
|2014||Apr||Started the collection of physics data with a nuclear target.|
|2014||Nov||Started the collection of physics data with a liquid hydrogen target after several operation tests.|
|2015||Apr||Restarted the collection of physics data with a nuclear target.|
BGOegg exp. LOI [Nov. 2012] English Version, Japanese Version
Quark-Nuclear Physics Division at ELPH
ELPH, Tohoku University
Laser Electron Photon Experiments at SPring-8 (LEPS/LEPS2)
RCNP, Osaka University
Advanced Meson Science Lab., RIKEN Nishina Center