I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Structure of 17 B studied by the quasifree neutron knockout reaction†
Z. H. Yang,∗1,∗2 Y. Kubota,∗2,∗3 A. Corsi,∗4,∗2 K. Yoshida,∗5 X. -X. Sun,∗6,∗7 J. G. Li,∗8 M. Kimura,∗9,∗10,∗1N. Michel,∗11,∗12 K. Ogata,∗1,∗13 C. X. Yuan,∗14 Q. Yuan,∗8 G. Authelet,∗4 H. Baba,∗2 C. Caesar,∗15 D. Calvet,∗4A. Delbart,∗4 M. Dozono,∗3 J. Feng,∗8 F. Flavigny,∗16 J. -M. Gheller,∗4 J. Gibelin,∗17 A. Giganon,∗4A. Gillibert,∗4 K. Hasegawa,∗18 T. Isobe,∗2 Y. Kanaya,∗19 S. Kawakami,∗19 D. Kim,∗20 Y. Kiyokawa,∗2M. Kobayashi,∗2 N. Kobayashi,∗21 T. Kobayashi,∗18,∗2 Y. Kondo,∗22,∗2 Z. Korkulu,∗20,∗23 S. Koyama,∗21,∗2V. Lapoux,∗4 Y. Maeda,∗19 F. M. Marqués,∗17 T. Motobayashi,∗2 T. Miyazaki,∗21,∗2 T. Nakamura,∗22,∗2N. Nakatsuka,∗24,∗2 Y. Nishio,∗25 A. Obertelli,∗4,∗2 A. Ohkura,∗25 N. A. Orr,∗17 S. Ota,∗3 H. Otsu,∗2 T. Ozaki,∗22V. Panin,∗2 S. Paschalis,∗15 E. C. Pollacco,∗4 S. Reichert,∗26 J. -Y. Roussé,∗4 A. T. Saito,∗22,∗2 S. Sakaguchi,∗25,∗2M. Sako,∗2 C. Santamaria,∗4 M. Sasano,∗2 H. Sato,∗2 M. Shikata,∗22,∗2 Y. Shimizu,∗2 Y. Shindo,∗25
L. Stuhl,∗20,∗2 T. Sumikama,∗18,∗2 Y. L. Sun,∗4 M. Tabata,∗25 Y. Togano,∗22,∗27,∗2 J. Tsubota,∗22 F. R. Xu,∗8J. Yasuda,∗25 K. Yoneda,∗2 J. Zenihiro,∗2 S. -G. Zhou,∗6,∗7 W. Zuo,∗11,∗12 and T. Uesaka∗2,∗28
The halo structure of weakly bound nuclei has been
a topic of great interest in recent decades not only as anovel phenomenon in itself, but also provides an important terrestrial model system to study the correlations
and properties of dilute neutron-rich matter.1)
In the present work, we have studied the structureof the halo nucleus 17 B by using the quasi-free (p, pn)reaction. This study concerns a kinematically complete
measurement, combining the high-intensity beams provided by the RIBF and the state-of-the-art detector
instruments including the vertex-tracking liquid hydrogen target MINOS, in-beam γ-ray spectrometer DALI2,
and the SAMURAI spectrometer.2)
Shown in Fig. 1 is the relative-energy (Erel ) spec†

Condensed from the article in Phys. Rev. Lett. 126, 082501(2021)∗1 Research Center for Nuclear Physics, Osaka University∗2 RIKEN Nishina Center∗3 Center for Nuclear Study, University of Tokyo∗4 IRFU, CEA, Université Paris-Saclay∗5 Advanced Science Research Center, Japan Atomic Energy
Agency∗6 Institute of Theoretical Physics, Chinese Academy of Sciences∗7 School of Physical Sciences, University of Chinese Academyof Sciences∗8 School of Physics and SKLNPT, Peking University∗9 Department of Physics, Hokkaido University∗10 Nuclear Reaction Data Centre, Hokkaido University∗11 Institute of Modern Physics, Chinese Academy of Sciences∗12 School of Nuclear Science and Technology, University of Chinese Academy of Sciences∗13 Department of Physics, Osaka City University∗14 Sino-French Institute of Nuclear Engineering and Technology,
Sun Yat-Sen University∗15 Institut für Kernphysik, Technische Universität Darmstadt∗16 IPN Orsay, Université Paris Sud∗17 LPC Caen, Université de Caen Normandie∗18 Department of Physics, Tohoku University∗19 Department of Applied Physics, University of Miyazaki∗20 Center for Exotic Nuclear Studies, Institute for Basic Science∗21 Department of Physics, University of Tokyo∗22 Department of Physics, Tokyo Institute of Technology∗23 Institute for Nuclear Research, Hungarian Academy of Sciences∗24 Department of Physics, Kyoto University∗25 Department of Physics, Kyushu University∗26 Physik Department, Technische Universität München∗27 Department of Physics, Rikkyo University∗28 Cluster for Pioneering Research, RIKEN

Fig. 1. 16 B Erel spectrum ﬁtted with a sum of four resonances (inset is a zoom-in view of the 0–1 MeV region).

trum of 15 B+n. It is well ﬁtted using four 16 B resonances, after considering the experimental acceptanceand resolutions. For each state of 16 B, the transverse
momentum distribution and production cross section
were analyzed by the distorted-wave impulse approximation (DWIA) reaction model.3) And the corresponding 1s1/2 and 0d5/2 spectroscopic factors of the knockout neutron were thus determined, giving a surprisingly
small 1s1/2 component (∼9%) in 17 B.
Our ﬁnding of such a small 1s1/2 component and thepreviously reported halo features in 17 B (e.g., Ref. 4))
can be well explained by the deformed relativistic
Hartree-Bogoliubov theory in continuum (DRHBc),5)
revealing a deﬁnite but not dominant halo component in17B. Our result gives the smallest s- or p-orbital component among known nuclei exhibiting halo features andimplies that the dominant occupation of s or p orbitals
is not a prerequisite for the occurrence of halo. The
halo component, whether or not dominant, results in a
distinctive diﬀused surface and, thus, manifests itself inreactions sensitive to the surface properties.
References
1) I. Tanihata et al., Prog. Part. Nucl. Phys. 68, 215 (2013).
2) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
3) T. Wakasa et al., Prog. Part. Nucl. Phys. 96, 32 (2017).
4) A. Estradé et al., Phys. Rev. Lett. 113, 132501 (2014).
5) X. -X. Sun et al., Phys. Lett. B 785, 530 (2018).

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