Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Neutron-neutron correlation in Borromean nucleus 11 Li
via the (p, pn) reaction
Y. Kubota,∗1,∗2 A. Corsi,∗3 G. Authelet,∗3 H. Baba,∗2 C. Caesar,∗4 D. Calvet,∗3 A. Delbart,∗3 M. Dozono,∗1J. Feng,∗5 F. Flavigny,∗6 J.-M. Gheller,∗3 J. Gibelin,∗7 A. Giganon,∗3 A. Gillibert,∗3 K. Hasegawa,∗8,∗2T. Isobe,∗2 Y. Kanaya,∗9,∗2 S. Kawakami,∗9,∗2 D. Kim,∗10,∗2 Y. Kiyokawa,∗1 M. Kobayashi,∗1 N. Kobayashi,∗11T. Kobayashi,∗8,∗2 Y. Kondo,∗12,∗2 Z. Korkulu,∗13,∗2 S. Koyama,∗11,∗2 V. Lapoux,∗3,∗2 Y. Maeda,∗9F. M. Marqués,∗7 T. Motobayashi,∗2 T. Miyazaki,∗11 T. Nakamura,∗12,∗2 N. Nakatsuka,∗14,∗2 Y. Nishio,∗15,∗2A. Obertelli,∗3,∗2 A. Ohkura,∗15,∗2 N. A. Orr,∗7 S. Ota,∗1 H. Otsu,∗2 T. Ozaki,∗12,∗2 V. Panin,∗2 S. Paschalis,∗4E. C. Pollacco,∗3 S. Reichert,∗16 J.-Y. Roussé,∗3 A. T. Saito,∗12,∗2 S. Sakaguchi,∗15,∗2 M. Sako,∗2C. Santamaria,∗3,∗2 M. Sasano,∗2 H. Sato,∗2 M. Shikata,∗12,∗2 Y. Shimizu,∗2 Y. Shindo,∗15,∗2 L. Stuhl,∗2T. Sumikama,∗8,∗2 M. Tabata,∗15,∗2 Y. Togano,∗12,∗2 J. Tsubota,∗12,∗2 T. Uesaka,∗2 Z. H. Yang,∗2J. Yasuda,∗15,∗2 K. Yoneda,∗2 and J. Zenihiro∗2Since a theoretical prediction was made by Migdal,1)a hypothetical bound state of two neutrons, dineutron, has attracted much attention. The neutronneutron correlation caused by the dineutron is expected to appear in weakly bound systems, such as
the Borromean nucleus 11 Li. There have been extensive studies to search for such a correlation in 11 Li.
E1 strengths deduced from Coulomb dissociation crosssections have been used by employing the E1 cluster sum rule to characterize their correlation.2) However, the model dependence was not negligible owing
to the 9 Li core excitation and the ﬁnal-state interactions.3) The kinematically complete measurement of
the quasi-free (p, pn) reaction was thus performed with
Borromean nuclei 11 Li, 14 Be, and 17,19 B at the RIBF so
as to determine the neutron momentum distributions
that provide more direct information of the groundstate correlation.4)The measurement required a high luminosity to haveas much statistics as possible. For this purpose, the15-cm-thick liquid hydrogen target MINOS5) was introduced. The SAMURAI spectrometer6) contributed
to minimize experimental biases originating from thegeometrical acceptance. A missing-mass setup composed of the neutron detector WINDS,7) the recoil proton detector RPD, and the gamma-ray detector array
DALI28) was newly conﬁgured for realizing the quasifree (p, pn) measurement.
As a measure of the dineutron correlation in 11 Li, theopening angle of two valence neutrons cos θY was reconstructed from momentum vectors of all the particles
involved in the reaction. The obtained cos θY distribution is shown in Fig. 1. The geometrical acceptanceof the experimental setup was corrected by performinga Monte-Carlo simulation. The asymmetric distribution indicates an admixture of diﬀerent parity states
and the dineutron correlation in 11 Li. The asymmetry obtained in the present work is weaker than thatin the previous work employing the neutron removal
reaction by using a carbon target.9) We presume thatthe dineutron correlation was overestimated in the previous study because of the sensitivity of Frithe
probe; theJan 19 05:55:00 2018probe used in the previous study is only sensitive tothe nuclear surface, where the dineutron correlation is
expected to develop.
× 103
Counts/ ε acc/0.1

600
400
200
0-1FitThis work9)
Ref. (scaled)
-0.5
00.5
Opening angle cosθ Y

1

Fig. 1. Opening-angle distribution cos θY for 11 Li. The
blue open and black closed marks represent the datataken in the present and previous works,9) respectively.

∗1Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center∗3 CEA, Saclay∗4 Department of Physics, Technische Universität Darmstadt∗5 Department of Physics, Peking University∗6 IPN Orsay∗7 LPC Caen
∗8 Department of Physics, Tohoku University∗9 Department of Applied Physics, University of Miyazaki∗10 Department of Physics, Ehwa Womans University∗11 Department of Physics, University of Tokyo∗12 Department of Physics, Tokyo Institute of Technology∗13 MTA Atomki∗14 Department of Physics, Kyoto University∗15 Department of Physics, Kyushu University∗16 Department of Physics, Technische Universität München∗2References1) A. B. Migdal, Sov. J. Nucl. Phys. 16, 238 (1973).
2) T. Nakamura et al., Phys. Rev. Lett. 96, 252502 (2006).
3) Y. Kikuchi et al., Phys. Rev. C 87, 034606 (2013).
4) Y. Kikuchi et al., Prog. Theor. Exp. Phys. 103D03 (2016).
5) A. Obertelli et al., Eur. Phys. Jour. A 50, 8 (2014).
6) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
7) J. Yasuda et al., Nucl. Instrum. Methods Phys. Res. B376, 393 (2016).
8) S. Takeuchi et al., Nucl. Instrum. Methods Phys. Res.
A 763, 596 (2014).
9) H. Simon et al., Phys. Rev. Lett. 83, 496 (1999).

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