Speaker
Description
The nuclear matter equation of state (EOS) is fundamental to understanding not only the bulk properties and structure of atomic nuclei but also various astrophysical phenomena, including neutron star mergers and supernova explosions.
The isoscalar giant monopole resonance (ISGMR) provides a direct constraint on the incompressibility of nuclear matter. In particular, the isospin-dependent term of the incompressibility, $K_\tau$, can be extracted from the centroid energies of the ISGMR. Previous experimental studies on stable Sn and Cd isotopes have reported values of $K_\tau$; however, the uncertainty remains large of about 100 MeV. Therefore, systematic ISGMR measurements including unstable nuclei, are required to improve the precision of $K_\tau$.
To enable systematic measurements, we have developed an active target system, CAT-M, designed for use with heavy-ion beams. As a first step toward systematic studies, ISGMR measurements were performed for Kr and Xe isotopes at the Heavy Ion Medical Accelerator in Chiba (HIMAC). A deuterium gas at a pressure of 40 kPa was used as the active target, and deuteron inelastic scattering was measured in inverse kinematics.
The CAT-M system consists of a Beam TPC, a Recoil TPC, silicon strip detectors (SSDs), and a dipole magnet. The trajectories of incoming beam particles were measured using the Beam TPC, while recoil particles were detected by the Recoil TPC and SSDs, performing track reconstruction. The reaction were reconstructed using the missing-mass spectroscopy. A multipole decomposition analysis was then performed, successfully extracting the ISGMR strength distribution. As a result, the centroid energy of the ISGMR in $^{86}$Kr was determined to be $17 \pm 1$ MeV. These results demonstrate the capability of the CAT-M for systematic ISGMR measurements including unstable nuclei.
In this presentation, we will report the result of $^{86}$Kr and current status of the systematic measurements, and discuss future prospects.