Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Study on 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 S. Koyama,∗11 V. Lapoux,∗3 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 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 M. Sasano,∗2 H. Sato,∗2 M. Shikata,∗12Y. Shimizu,∗2 Y. Shindo,∗15 L. Stuhl,∗2 T. Sumikama,∗8 M. Tabata,∗15 Y. Togano,∗12 J. Tsubota,∗12T. Uesaka,∗2 Z. H. Yang,∗2 J. Yasuda,∗15 K. Yoneda,∗2 and J. Zenihiro∗2Table 1. Estimated resolution of momentum vectors deduced from the detector responses and angular straggling. The unit is MeV/c.

Dineutron correlation is one of the speciﬁc phenomena expected to appear in neutron drip-line nuclei.
It has been explored through indirect studies such as
the determination of the E1 cluster sum rule via theCoulomb breakup reaction.1) In order to directly determine the momentum distribution of two valence neutrons of the Borromean nuclei 11 Li, 14 Be, and 17,19 B, akinematically complete measurement was performed at
the RIKEN RIBF for the quasi-free (p, pn) reaction onthese nuclei.2) The opening angle between the two neutrons was reconstructed from the measured momentum
vectors of all the particles.
The experiment was carried out by using the SAMURAI spectrometer3) combined with the liquid hydrogentarget system MINOS.4) The beam momentum was determined from the time-of-ﬂight (TOF) between focal
planes F7 and F13. The trajectory was measured using the beam drift chambers (BDCs). The momentum vectors of a decay neutron, a knocked-out neutron, and a recoil proton were determined from theTOF and position respectively measured by the NEBULA, the WINDS, and a recoil proton detector (RPD).
The position and the angle of a heavy fragment at theentrance and the exit of the SAMURAI spectrometer
were measured by the forward drift chambers (FDCs).
The rigidity was determined so as to reproduce theset of the tracking information by using the calculated
magnetic ﬁeld.
The resolution of each momentum vector, estimatedfrom the detector responses and angular straggling

Particle
Beam 11 Li
Recoil p
Knocked-out nDecay nFragment 9 LiTotalDetector
BigRIPS+BDC
RPD
WINDS
NEBULA
FDCσP x0.08
12150.2
0.1
20σP y0.08
10160.2
0.1
19σP z8121551225

around the target, is summarized in Table 1. The momentum resolution of the recoil proton was dominatedby the angular straggling, while that of the knockedout neutron was limited by the time resolution of theWINDS. The required resolution of about 20 MeV/cwas achieved.
Figures 1 (a), (b), (c), and (d) show the diﬀerence ofthe sum of the four-vectors of all the particles between
the initial and the ﬁnal states projected onto the x-,y-, and z-direction and the energy, respectively. Owing to the momentum and energy conservation law, ineach spectrum the peak should be centered at zero;
this is a test of the consistency of both the reconstruction and measurement. The widths of the spectra areconsistently explained by the estimated resolution.
Data analysis is currently in progress.
10008006004002000-150 -100 -50(a)800
7006005004003002001000-150 -100 -50

σ = 20.80(c)∗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∗250 100 150
dPx [MeV/c]
σ = 25.3050 100 150
dPz [MeV/c]

(b)

1000
800
600
400
2000-150 -100 -5001400
1200
1000
800
600
400
2000-150 -100 -5050 100 150
dPy [MeV/c]

050 100 150
dE [MeV]σ = 18.9(d)Fig. 1. Spectra showing the consistency of the reconstruction in the (a) x-, (b) y-, and (c) z-direction, and (d)the energy via the veriﬁcation of the momentum andenergy conservation.

References
1) T. Nakamura et al.: Phys. Rev. Lett. 96, 252502 (2006).
2) Y. Kubota et al.: RIKEN Accel. Prog. Rep. 48, 52 (2015).
3) T. Kobayashi et al.: Nucl. Instr. Meth. B317, 294 (2013).
4) A. Obertelli et al.: Eur. Phys. Jour. A50, 8 (2014).

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