The possible existence of eta-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the eta mass at finite density, which is expected to be reduced because of the interplay between the $U_A(
1)$ anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed.
The mass of the {eta} meson is theoretically expected to be reduced at finite density, which indicates the existence of {eta}-nucleus bound states. To investigate these states, we perform missing-mass spectroscopy for the (p, d) reaction near the {et
a} production threshold. The overview of the experimental situation is given and the current status is discussed.
We calculate theoretically the formation spectra of eta(958)-nucleus systems in the (p,d) reaction for the investigation of the in-medium modification of the eta mass. We show the comprehensive numerical calculations based on a simple form of the eta
optical potential in nuclei with various potential depths. We conclude that one finds an evidence of possible attractive interaction between eta and nucleus as peak structure appearing around the eta threshold in light nuclei such as 11C when the attractive potential is stronger than 100 MeV and the absorption width is of order of 40 MeV or less. Spectroscopy of the (p,d) reaction is expected to be performed experimentally at existing facilities, such as GSI. We also estimate the contributions from the omega and phi mesons, which have masses close to the eta meson, concluding that the observation of the peak structure of the eta-mesic nuclei is not disturbed although their contributions may not be small.
We have developed a prototype time-resolved neutron imaging detector employing the micro-pixel chamber (muPIC), a micro-pattern gaseous detector, coupled with a field programmable gate array-based data acquisition system for applications in neutron r
adiography at high-intensity neutron sources. The prototype system, with an active area of 10cm x 10cm and operated at a gas pressure of 2 atm, measures both the energy deposition (via time-over-threshold) and 3-dimensional track of each neutron-induced event, allowing the reconstruction of the neutron interaction point with improved accuracy. Using a simple position reconstruction algorithm, a spatial resolution of 349 +/- 36 microns was achieved, with further improvement expected. The detailed tracking allows strong rejection of background gamma-rays, resulting in an effective gamma sensitivity of 10^-12 or less, coupled with stable, robust neutron identification. The detector also features a time resolution of 0.6 microseconds.
