Spectroscopy of η′ Mesic Nuclei via Semi-Exclusive Measurement at FAIR

In order to investigate a possible mass reduction of an η′ meson at finite density, a series of missing-mass spectroscopy experiments of η′-nucleus bound states with the 12C(p,d) reaction is planned at GSI and FAIR. A semi-exclusive measurement with the tagging of protons from η′ two-body absorption (η′NN → NN) will be a key feature in an experiment with Super-FRS at FAIR

Spectroscopy of η\eta′ Mesic Nuclei via Semi-Exclusive Measurement at FAIR

In order to investigate a possible mass reduction of an η′ meson at finite density, a series of missing-mass spectroscopy experiments of η′-nucleus bound states with the 12C(p,d) reaction is planned at GSI and FAIR. A semi-exclusive measurement with the tagging of protons from η′ two-body absorption (η′NN → NN) will be a key feature in an experiment with Super-FRS at FAIR

Missing Mass Spectroscopy of

We plan a missing-mass spectroscopy experiment of η′ mesic nuclei with the 12C(p,d)η′⊗11C reaction to study in-medium properties of the η′ meson. In nuclear medium, due to restoration of chiral symmetry, the mass of the η′ meson may be reduced, and η′ bound states in a nucleus may exist. The experiment will be started at GSI with a 2.5 GeV proton beam using FRS as a spectrometer and will be continued at Super-FRS at FAIR. The plan of the experiment and development of a Cherenkov detector and an optics mode are described

Pionic atom unveils hidden structure of QCD vacuum

Modern theories of physics tell that the vacuum is not an empty space. Hidden in the vacuum is a structure of anti-quarks $\bar{q}$ and quarks $q$. The $\bar{q}$ and $q$ pair has the same quantum number as the vacuum and condensates in it since the strong interaction of the quantum chromodynamics (QCD) is too strong to leave it empty. The $\bar{q}q$ condensation breaks the chiral symmetry of the vacuum. The expectation value $$ is an order parameter. For higher temperature or higher matter-density, $||$ decreases reflecting the restoration of the symmetry. In contrast to these clear-cut arguments, experimental evidence is so far limited. First of all, the $\bar{q}q$ is nothing but the vacuum itself. It is neither visible nor perceptible. In this article, we unravel this invisible existence by high precision measurement of pionic atoms, $\pi^-$-meson-nucleus bound systems. Using the $\pi^-$ as a probe, we demonstrate that $||$ is reduced in the nucleus by a factor of 58 $\pm$ 4% compared with that in the vacuum. This reduction indicates that the chiral symmetry is partially restored due to the extremely high density of the nucleus. The present experimental result clearly exhibits the existence of the hidden structure, the chiral condensate, in the vacuum

The first precision measurement of deeply bound pionic states in

We performed a precision missing-mass spectroscopy experiment of the deeply bound pionic states in a 121Sn atom using the (d,3He) reaction near the π− emission threshold. The experiment serves as a pilot experiment for our new ‘pionic atom factory project’ at RIBF, which aims at precision spectroscopy of the energy spectrum of the pionic atom of isotopes and isotones. The result of the pilot experiment demonstrated the potentiality of BigRIPS and of the RIBF facilities for the project. The current status of the analysis is reported

The first precision measurement of deeply bound pionic states in 121^{121}Sn

We performed a precision missing-mass spectroscopy experiment of the deeply bound pionic states in a 121Sn atom using the (d,3He) reaction near the π− emission threshold. The experiment serves as a pilot experiment for our new ‘pionic atom factory project’ at RIBF, which aims at precision spectroscopy of the energy spectrum of the pionic atom of isotopes and isotones. The result of the pilot experiment demonstrated the potentiality of BigRIPS and of the RIBF facilities for the project. The current status of the analysis is reported