Speaker
Description
Pions (Yukawa particles) mediate the strong interaction between nucleons and play a crucial role in the formation and stability of atomic nuclei. Their influence manifests through tensor forces and three-body forces, significantly contributing to nuclear binding and saturation properties—yet many aspects remain poorly understood. In particular, pions are essential in connecting low- and high-momentum components of nucleons, thereby generating a large portion of the nuclear binding energy. In this sense, they represent the “essence” of nuclear stability. Moreover, the widespread generation of high-momentum nucleons by pions throughout the nucleus may be regarded as the “reality” of nuclear structure.
While conventional experimental approaches have struggled to probe the detailed behavior of pions inside nuclei, this study aims to achieve direct observation using high-quality proton beams and a high-resolution magnetic spectrometer at RCNP. We will employ the pion knockout ($p, pπ$) reaction, which introduces high-momentum components into the nucleus at low excitation energy while simultaneously injecting the quantum numbers of a pion (J$^π$ = 0$^-$). This reaction is expected to selectively populate unnatural-parity states in the residual nucleus.
Through this experimental approach, we aim to elucidate the following:
- The contribution of pions to nuclear binding energy
- The role of pions in generating high-momentum nucleons within the nuclear medium
- The effect of three-body forces mediated by delta resonances on nuclear stability
- The possible emergence of a novel giant resonance associated with pion dynamics (“pionic modes”)
Traditional nuclear theories based on the shell model incorporate the effects of pions as part of an effective potential that governs nucleon behavior. However, comparisons with experimental results from Jefferson Lab have revealed that this framework fails to reproduce the high-momentum components observed in nucleon momentum distributions. Addressing this discrepancy requires treating pions as explicit degrees of freedom on par with nucleons. To this end, we apply many-body quantum theoretical approaches developed in the study of strongly correlated electron systems to achieve a detailed understanding of pion-involved nuclear excitations—so-called pionic modes.
This presentation introduces a planned measurement of pion knockout reactions using the double-arm spectrometer at RCNP, aiming to explore pion dynamics in nuclei.
| Email address | junki@rcnp.osaka-u.ac.jp |
|---|---|
| Classification | Ion optics and spectrometers |
