Missing mass spectroscopy with large acceptance spectrometer SAMURAI

SAMURAI (Superconducting Analyzer for Multi-particles from Radioisotope beams) is a large-acceptance multi-particle spectrometer[1] at RIKEN RIBF. The main part of the system is a superconducting dipole magnet with 7 Tm bending power for the momentum analysis of heavy projectile fragments including protons. The 80-cm gap also enables measurements of multi neutrons with beam rapidity. This system is suitable for various radioactive-beam experiments such as electromagnetic dissociation including radiative-capture reactions, various direct reactions as well as polarized-deuteron-induced reactions and EoS studies.

We started experimental campaign in SAMURAI with a series of invariant-mass measurements by taking advantage of the common experimental setup. Although the invariant-mass spectroscopy is a powerful tool to study low-lying unbound states, both the resolution and the efficiency drop down with increasing the excitation energy. This difficulty can be overcome by employing the complementary technique, the missing-mass spectroscopy.

Since 2014, 8 missing-mass measurements have been conducted. The large acceptance of SAMURAI enables not only to minimize the experimental biases but also to tag the decay modes which is technically important to make a trigger with an intense beam. It should be noted that the energy and the scattering angle of the recoil particle to be detected are widely ranged in the laboratory frame and the kinematics strongly depends on the interest. It causes a technical difficulty to share the experimental setup among different measurements.

In this talk, recent physics results as well as future perspectives will be presented.

 

References

[1] T. Koyabashi et al.,  Nucl. Instr. Meth. Phys. Res. B 317, 294 (2013).