Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Study of neutron-neutron correlation in Borromean nuclei
via the (p, pn) reaction with the SAMURAI spectrometer
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 T. Isobe,∗2Y. Kanaya,∗9 S. Kawakami,∗9 D. Kim,∗10 Y. Kiyokawa,∗1 M. Kobayashi,∗1 N. Kobayashi,∗11 T. Kobayashi,∗8Y. Kondo,∗12 Z. Korkulu,∗13,∗2 S. Koyama,∗11 V. Lapoux,∗3,∗2 Y. Maeda,∗9 F. M. Marqués,∗7 T. Motobayashi,∗2T. Miyazaki,∗11 T. Nakamura,∗12 N. Nakatsuka,∗14,∗2 Y. Nishio,∗15 A. Obertelli,∗3,∗2 A. Ohkura,∗15 N. A. Orr,∗7S. Ota,∗1 H. Otsu,∗2 T. Ozaki,∗12 V. Panin,∗2 S. Paschalis,∗4 E. C. Pollacco,∗3 S. Reichert,∗16 J.-Y. Roussé,∗3A. T. Saito,∗12 S. Sakaguchi,∗15 M. Sako,∗2 C. Santamaria,∗3,∗2 M. Sasano,∗2 H. Sato,∗2 M. Shikata,∗12Y. Shimizu,∗2 Y. Shindo,∗15 L. Stuhl,∗2 T. Sumikama,∗8,∗2 M. Tabata,∗15 Y. Togano,∗12 J. Tsubota,∗12T. Uesaka,∗2 Z. H. Yang,∗2 J. Yasuda,∗15 K. Yoneda,∗2 and J. Zenihiro∗2Dineutron correlation is one of the phenomena expected to appear in neutron-drip-line nuclei. It haslong been presumed that the dineutron correlation isa key ingredient to understand the binding mechanismand exotic structures of these nuclei. E1 strengths
often deduced in previous Coulomb breakup studies
have been used by employing the E1 cluster sum
rule to characterize their correlation.1) However, themodel dependence was not negligible owing to the 9 Li
core excitation and the ﬁnal state interactions.2) 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 todetermine the neutron momentum distributions that
help characterize the correlation.3) The opening angle
between the two neutrons was reconstructed from themeasured momentum vectors of all the particles.
The experiment was conducted using the SAMURAI spectrometer4) and the liquid hydrogen target system MINOS.5) The beam momentum was determinedfrom the time of ﬂight (TOF) between focal planes
F7 and F13. The trajectory was measured by beamdrift chambers (BDCs). The momentum vectors of
the neutron knocked out from 11 Li, another emitted
from the resulting 10 Li residue, and the recoil proton
were determined from the TOF and position measured
by neutron telescopes WINDS and NEBULA, and arecoil proton detector (RPD), respectively. The position and angle of 9 Li at the entrance and exit of theSAMURAI spectrometer were measured by forward

drift chambers (FDCs). The magnetic rigidity was determined from the tracking information thus obtained.
The magnetic ﬁeld of the spectrometer was calculated
and taken into account. The relative energy Erel ofthe reaction residue 10 Li, the missing momentum of
the knocked-out neutron in the ground-state 11 Li, andthe opening angle cos θY of two valence neutrons in11
Li were reconstructed from the obtained momentumvectors.
Figure 1 shows the cos θY dependence of Erel .
Smaller cos θY values are highly favored as Erel decreases, while the yields are evenly distributed overcos θY at a higher Erel . Because the small Erel value
corresponds to the surface region of the nucleus,6) thisresult suggests that the dineutron correlation is much
more developed in the surface region. This is qualitatively consistent with the theoretical prediction.7)

Relative energy E rel [MeV]10810264
20-1∗1

Center 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

10∗2

1-0.5
00.5
Opening angle cosθ Y1Fig. 1. Erel vs. cos θY plot for the 11 Li(p, pn)9 Li + n reaction.

References1) T. Nakamura et al., Phys. Rev. Lett. 96, 252502 (2006).
2) Y. Kikuchi et al., Phys. Rev. C 87, 034606 (2013).
3) Y. Kubota et al., RIKEN Accel. Prog. Rep. 48, 52 (2015).
4) T. Kobayashi et al., Nucl. Instr. Meth. B317, 294 (2013).
5) A. Obertelli et al., Eur. Phys. Jour. A50, 8 (2014).
6) Y. Kikuchi et al., Prog. Theor. Exp. Phys. 2016,103D03 (2016).
7) A. B. Migdal, Soviet J. Nucl. Phys. 16, 238 (1973).

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