Speaker
Description
In neutrino observations, search for the diffuse supernova neutrino background and precise measurements of neutrino oscillation are ongoing, aiming to probe the history of the universe and leptonic CP violation, respectively. These studies involve neutrino–nucleus interactions in the energy range of several tens to several hundreds of MeV, where quasielastic scattering is the dominant interaction mode. In Super-Kamiokande, however, significant uncertainties remain in the predictions of neutrino-oxygen interactions and subsequent nucleon-oxygen interactions, which limits the sensitivity to these physical goals.
These interactions lead to nuclear de-excitation, producing gamma-rays and neutrons that are observable in the detector. In particular, neutrons are captured on gadolinium and detected without an energy threshold. Therefore, a precise understanding of gamma-ray and neutron emissions from nuclear de-excitation process is important for improving the accuracy of prediction. However, since many de-excitation products have low energies and are difficult to detect, experimental data on nuclear de-excitation processes are currently very limited.
To address this issue, we plan to conduct the SAMURAI-79 experiment, an inverse kinematics experiment at RIBF, RIKEN. In this experiment, the excited nuclei $\mathrm{^{15}N^*}$, $\mathrm{^{15}O^*}$, and $\mathrm{^{16}O^*}$ are produced via nucleon knockout reactions using an oxygen beam and a hydrogen target. By employing inverse kinematics, the de-excitation products are boosted in the laboratory frame, enabling to efficiently detect low-energy particles. The excitation energies of these nuclei are reconstructed by detecting recoil nucleons, and their subsequent de-excitation processes are measured with the SAMURAI spectrometer [1].
Using the data obtained in this experiment, the parameters of the Hauser-Feshbach compound nuclear model will be tuned with the nuclear reaction calculation code CCONE. Based on the tuned model, nuclear data for oxygen will be constructed and planned to be implemented into Geant4 and the neutrino event generator NEUT. This will reduce the uncertainties in the prediction of gamma-ray and neutron emission from neutrino-oxygen interactions.
For precise reconstruction of the excitation energy, we are developing a neutron detector MNEUT to detect recoil neutron. During the beamtime in June 2025, we conducted a parasitic measurement to evaluate its performance. In this talk, we will present an overview of the SAMURAI-79 experiment and the current preparation status, including the performance evaluation of MNEUT and the development of the tuning procedure for the compound nuclear model.
[1]: T. Kobayashi et al., NIMB 317, 294 (2013)