Outline of Planned Research

Program A02 Investigation of deep inside of nuclei and neutron stars with high energy photons
Principal Investigator NAKAMURA, Satoshi N. (The University of Tokyo)

We will perform precise electromagnetic spectroscopy of Λ hypernuclei using virtual and real photons produced from the high energy electron beam obtained at Thomas Jefferson National Accelerator Facility (JLab, USA), Mainz Microtron (MAMI, Germany) and ELPH-Tohoku Univ. The study will enable us to measure Charge Symmetry Breaking (CSB) of the Λ ΛN interactions, isospin dependence of heavy hypernuclei with unprecedented accuracy and dramatically deepening the knowledge of baryonic force which is essential to solve the heavy neutron star puzzle (Hyperon Puzzle).

Particles called hyperons, including strange quarks, can be discussed in the same frame work (SU(3) symmetry) to protons and neutrons that make up the usual nuclei, and the hyperon can be a component of a nucleus. Nuclei including strange quarks are called "hypernuclei". Hypernuclei do not exist naturally on the earth, however, the possibility is seriously discussed that hyperons exist naturally in the center of a compact star called a neutron star, which is the densest substance in the universe. The neutron star is a huge single nucleus with a radius of about 10 km and the gravitational wave was observed from the neutron star merger in 2017. A possibility that elements heavier than iron were made by the neutron star merger was discussed and neutron star is now a very hot research subject.

The relation between the mass and size of a neutron star can be derived from its Equation of State (equation describing its stiffness), but based on the knowledge of the conventional baryonic force, the maximum mass of the neutron star including hyperons cannot exceed about 1.6 times solar mass. This situation is similar that a huge Tofu (soya cake) is crushed by its own weight and Tofu of the building size cannot be made. However, in recent years, neutron stars with twice the solar mass were observed, and neutron stars were found to be "harder" than we thought. This problem is called "hyperon puzzle" and it is an extremely important problem to be solved in nuclear physics. In order to solve this problem, it is essential to have a deep understanding of the baryonic force in neutron rich and high density environment, but it is impossible to directly observe the central part of the neutron star to investigate it. Therefore, we will proceed experiments to artificially create hypernuclei, which are miniatures in the center of neutron stars, using virtual photons at the powerful electron accelerator facilities to investigate its properties.

A Λ Hypernuclus is electro-magnetically produced by using virtual photon.
The experimental site: Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson National Accelerator Facility(JLab) in USA.

Members

Principal Investigator NAKAMURA, Satoshi N.
(The University of Tokyo)
Co-Investigator FUJII, Yuu (Tohoku Medical and Pharmaceutical University)  
Research Collaborators NAGAO, Sho（Tohoku University)  
KANETA, Masashi (Tohoku University）  
GOGAMI, Toshiyuki (Kyoto University）  
ISHIKAWA, Takatsugu（Tohoku University）  
HIYAMA, Emiko（Tohoku University & RIKEN）  
AZUMA, Toshiyuki (RIKEN)  
KINO, Yasushi (Tohoku University)  
NOMACHI, Masaharu (Osaka University)  

Reference Materials

  • T. Gogami et al., “Experimental techniques and performance of Λ-hypernuclear spectroscopy with the (e, e'K+) reaction,” Nucl. Instrum. Methods Phys. Res. A 900, 69–83 (May 2018), DOI: 10.1016/j.nima.2018.05.042 .
  • S. N. Nakamura, T. Gogami, L. Tang for the JLab Hypernuclear Collaboration, “Spectroscopic study of Λ hypernuclei with electron beams at Jefferson Lab,” JPS Conf. Proc. 17, 011002-1–13 (2017), DOI: 10.7566/JPSCP.17.011002 .
  • T. Gogami, … ,Y. Fujii, … , M. Kaneta, S. Nagao, S. N. Nakamura et al. (HKS (JLab E05-115) Collaboration), “Spectroscopy of the neutron-rich hypernucleus 7ΛHe from electron scattering,” Phys. Rev. C 94, 021302(R)-1–6 (August 2016) DOI: 10.1103/PhysRevC.94.021302 .
  • T. Gogami, … , Y. Fujii, … , M. Kaneta, S. Nagao, S. N. Nakamura et al. (HKS (JLab E05-115) Collaboration), “High resolution spectroscopic study of 10ΛBe,” Phys. Rev. C 93, 034314-1–7 (March 2016), DOI: 10.1103/PhysRevC.93.034314 .
  • A. Esser, S. Nagao, … , Y. Fujii, T. Gogami, … , M. Kaneta, … , S. N. Nakamura et al. (A1 Collaboration), “Observation of 4ΛH hyperhydrogen by decay-pion spectroscopy in electron scattering,” Phys. Rev. Lett. 114, 232501-1–5 (June 2016), DOI: 10.1103/PhysRevLett.114.232501 .