II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Observation of low-lying dipole states in the 11 Li(p, n) reaction
L. Stuhl,∗1,∗2,∗3 M. Sasano,∗3 J. Gao,∗3,∗4 Y. Hirai,∗5 K. Yako,∗2 T. Wakasa,∗5 D. S. Ahn,∗3 H. Baba,∗3A. I. Chilug,∗6,∗3 S. Franchoo,∗7 Y. Fujino,∗8 J. Gibelin,∗9 I. S. Hahn,∗1,∗10 Z. Halász,∗11 T. Harada,∗12
M. N. Harakeh,∗13,∗14 D. Inomoto,∗5 T. Isobe,∗3 H. Kasahara,∗5 D. Kim,∗1,∗15 G. G. Kiss,∗11 T. Kobayashi,∗16,∗3Y. Kondo,∗17,∗3 Z. Korkulu,∗1,∗3 S. Koyama,∗18,∗3 Y. Kubota,∗3 A. Kurihara,∗17 H. N. Liu,∗19 M. Matsumoto,∗17S. Michimasa,∗2 H. Miki,∗17,∗3 M. Miwa,∗20,∗3 T. Motobayashi,∗3 T. Nakamura,∗17,∗3 M. Nishimura,∗3 H. Otsu,∗3V. Panin,∗3 S. Park,∗10 A. T. Saito,∗17,∗2 H. Sakai,∗3 H. Sato,∗3 T. Shimada,∗17 Y. Shimizu,∗3 S. Shimoura,∗2A. Spiridon,∗6 I. C. Stefanescu,∗6 X. Sun,∗3,∗4 Y. L. Sun,∗19 H. Suzuki,∗3 E. Takada,∗21 Y. Togano,∗8,∗3T. Tomai,∗17,∗3 L. Trache,∗6 D. Tudor,∗6,∗3 T. Uesaka,∗3 H. Yamada,∗17 M. Yasuda,∗17 K. Yoneda,∗3 K. Yoshida,∗3J. Zenihiro,∗3 and N. Zhang∗22,∗2
The SAMURAI30 experimental program aims to systematically investigate the isovector response of light nuclei near the neutron drip line.1) No data are available
on spin-isospin collectivity for nuclei with large isospin
asymmetry factors, where (N − Z)/A > 0.25. GamowTeller (GT) and spin-dipole (SDR) transitions, including their giant resonances, were studied on 11 Li and14Be using charge-exchange (p,n) reactions in inverse
kinematics combined with the missing-mass technique.2)
The setup of the PANDORA low-energy neutron timeof-ﬂight counter3) and SAMURAI magnetic spectrometer,4) as well as a thick liquid hydrogen target, enables
us to perform measurements with high luminosity. In
our previous experiments at RIKEN RIBF on 132 Sn, wesuccessfully demonstrated5) that we can obtain data on
unstable nuclei in the giant-resonance region with similar
statistics as data obtained on stable nuclei.
Preliminary results on GT giant resonance are alreadydetailed in a previous report.6) More than ﬁfteen diﬀerent decay channels were identiﬁed for the 11 Be reaction
product. A strong GT transition at 19 MeV, in agreement with previous beta-decay studies, was observed.
We showed experimental evidence for the GT peak shifting below the Isobar Analog State (IAS).
In 11 Be,10 Be, and 9 Be related decay channels, lowlying states were also identiﬁed in the excitation energy∗1Center for Exotic Nuclear Studies, Institute for Basic Science∗2 Center for Nuclear Study, University of Tokyo∗3 RIKEN Nishina Center∗4 School of Physics, Peking University∗5 Department of Physics, Kyushu University∗6 Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering∗7 Institut de Physique Nucléaire, Université Paris-Saclay∗8 Department of Physics, Rikkyo University∗9 Nuclear Physics Laboratory, LPC CAEN
∗10 Department of Physics, Ewha Womans University∗11 Institute for Nuclear Research (ATOMKI)∗12 Department of Physics, Toho University∗13 Department of Physics, University of Groningen∗14 GSI Helmholtzzentrum für Schwerionenforschung∗15 Department of Physics, Korea University∗16 Department of Physics, Tohoku University∗17 Department of Physics, Tokyo Institute of Technology∗18 Department of Physics, University of Tokyo∗19 Départment de Physique Nucléaire, CEA, Université ParisSaclay∗20 Department of Physics, Saitama University∗21 National Institute of Radiological Sciences (NIRS)∗22 Institute of Modern Physics, Chinese Academy of Sciences  

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 Fig. 1. Low-liying dipole states in excitation energy spectrum
in the 4◦ –6◦ (a) and 8◦ –10◦ (b) center-of-mass angularbins for beryllium-related decay channels.

range below 10 MeV. The angular-momentum distributions of these states show a peak at backward angles,
which is characteristic of dipole transitions. Similar lowlying SD states were predicted in previous theoretical
calculations on 11 Li by Suzuki7) in connection to theneutron-halo structure.
References
1) L. Stuhl et al., RIKEN Accel. Prog. Rep. 48, 54 (2015).
2) M. Sasano et al., Phys. Rev. Lett. 107, 202501 (2011).
3) L. Stuhl et al., Nucl. Instrum. Methods Phys. Res. A 866,164 (2017).
4) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
5) J. Yasuda et al., Phys. Rev. Lett. 121, 132501 (2018).
6) L. Stuhl et al., RIKEN Accel. Prog. Rep. 53, 38 (2019).
7) T. Suzuki et al., Nucl. Phys. A 662, 282 (2000).

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