Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 52 (2019)

Gamow–Teller giant resonance in 132 Sn
M. Sasano,∗1 J. Yasuda,∗2 L. Stuhl,∗1,∗6 R. G. T. Zegers,∗3 H. Baba,∗1 W. Chao,∗1 M. Dozono,∗1 N. Fukuda,∗1N. Inabe,∗1 T. Isobe,∗1 G. Jhang,∗1,∗13 D. Kamaeda,∗1 T. Kubo,∗1 M. Kurata-Nishimura,∗1 E. Milman,∗1T. Motobayashi,∗1 H. Otsu,∗1 V. Panin,∗1 W. Powell,∗1 M. Sako,∗1 H. Sato,∗1 Y. Shimizu,∗1 H. Suzuki,∗1T. Suwat,∗1 H. Takeda,∗1 T. Uesaka,∗1 K. Yoneda,∗1 J. Zenihiro,∗1 T. Kobayashi,∗1,∗4 T. Sumikama,∗1,∗4T. Tako,∗4 T. Nakamura,∗5 Y. Kondo,∗5 Y. Togano,∗5 M. Shikata,∗5 J. Tsubota,∗5 K. Yako,∗6 S. Shimoura,∗6S. Ota,∗6 S. Kawase,∗6 Y. Kubota,∗6 M. Takaki,∗6 S. Michimasa,∗6 K. Kisamori,∗6 C. S. Lee,∗6 H. Tokieda,∗6M. Kobayashi,∗6 S. Koyama,∗7 N. Kobayashi,∗7 H. Sakai,∗1 T. Wakasa,∗2 S. Sakaguchi,∗2 A. Krasznahorkay,∗8T. Murakami,∗9 N. Nakatsuka,∗9 M. Kaneko,∗9 Y. Matsuda,∗10 D. Mucher,∗11 S. Reichert,∗11 D. Bazin,∗3and J. W. Lee∗12Among collective modes,1) the Gamow-Teller (GT)
giant resonance is an interesting excitation mode. It
is a 0h̄ω excitation characterized by the quantumnumber changes in orbital angular momentum (∆L =0), spin (∆S = 1), and isospin (∆T = 1), and it isinduced by the transition operator στ . In stable nuclei
in medium or heavier mass regions (A > 50), the collectivity in this mode exhibits the GT giant resonance(GTGR), which provides information that is criticallyimportant for understanding the isovector part of theeﬀective nucleon-nucleon interaction2) and the symmetry potential of the equation of state.3) In particular,
the understanding of the short-range repulsive part ofthe eﬀective interaction, i.e., so-called Landau-Migdal(LM) force in the spin-isospin channel, is crucial in
the prediction of the onset of the pion condensationin nuclear matters such as a neutron star.4) Recently,
we have been rapidly expanding the domain of GTGR
studies at RIBF in the nuclear chart.5,6) This provides
a new opportunity to evaluate the strength of the LMforce and the so-called LM parameter g ′ for an unstable nucleus.
In this study, an experiment at RIBF was performed
in March 2014 to extract the GT transition strengths
over a wide excitation energy range covering their giant resonances on the key doubly magic nucleus 132 Sn.
The purpose of the experiment was to calibrate theg ′ parameter through observating the GTGR in 132 Sn.
This is also an essential step toward establishing thecomprehensive theoretical models for the nuclei locatedbetween 78 Ni and 208 Pb. Details of the experimental setups and analysis are already given in previous
progress reports and the results have been recently
published in Ref. 7). Data for the GTGR were ob-tained almost in the same quality as the stable-beamexperiments, which opens up a new age of GR studies with RI beams in the ﬁeld of experimental nuclear
physics. The obtained g ′ parameter was 0.68 ± 0.07.
In comparison to the values obtained for the stable
nuclei 90 Zr and 208 Pb, it indicates that g ′ is kept almost constant over a region of isospin asymmetry from(N − Z)/A = 0.11 to 0.24 and from mass number
A = 90 to 208. It also indicates that pion condensation occurs in the inner part of a neutron star whosemass is 1.4 times heavier than the solar mass.
We are grateful to the RIKEN RIBF accelerator
crew and CNS, University of Tokyo, for their eﬀorts
and support to operate the RI beam factory. We
thank M. Ichimura, E. Litvinova, C. Robin, Y. F. Niu,G. Colo, H. Z. Liang, and Z. M. Niu for our valuable
discussions. This work was supported in part by aGrant-in-Aid for Scientiﬁc Research (No. 274740187),
Grant-in-Aid for the Japan Society for the Promotionof Science (JSPS) Research Fellow (No. 265720), JSPS
KAKENHI Grant No. 16H02179 from the Japan Society for the Promotion of Science, MEXT KAKENHI
Grant No. 24105005, US NSF PHY-1430152 (JINA
Center for 606 the Evolution of the Elements), US NSF
PHY-1565546, and the Hungarian NKFI Foundation[K124810].
References
1) M. N. Harakeh, A. M. van der Woude, Giant Resonances (Oxford University Press, Oxford, 2001).
2) S. Fracasso, G. Colo, Phys. Rev. C 72, 064310 (2005).
3) P. Danielewicz, Nucl. Phys. A 727, 233 (2003).
4) A. B. Migdal, Rev. Mod. Phys. 50, 107 (1978).
5) M. Sasano et al., Phys. Rev. Lett. 107, 202501 (2011).
6) M. Sasano et al., Phys. Rev. C 86, 034324 (2012).
7) M. Sasano et al., Phys. Rev. Lett. 121, 132501 (2018).

∗1

RIKEN Nishina Center
Department of Physics,Kyushu University∗3 NSCL, Michigan State University∗4 Department of Physics, Tohoku University∗5 Department of Physics, Tokyo Institute of Technology∗6 CNS, University of Tokyo∗7 Department of Physics, University of Tokyo∗8 MTA, Atomki∗9 Department of Physics, Kyoto University∗10 Department of Physics, Konan University∗11 Department of Physics, Technical University Munich∗12 Department of Physics, Korea University∗2-2-