Study of Neutron-Proton Correlations & 3N Forces in 12C

H. N. Liu,∗1,∗2 J. Lee,∗1,∗3 H. Otsu,∗1 Y. Kondo,∗4 S. Takeuchi,∗1 Y. Togano,∗4 H. Baba,∗1 N. Chiga,∗5

P. Doornenbal,∗1 N. Fukuda,∗1 J. Gibelin,∗6 J. Hwang,∗7 T. Isobe,∗1 T. Kawabata,∗8 N. Kobayashi,∗9

T. Kobayashi,∗5 K. Kusaka,∗1 S. Leblond,∗6 Y. Matsuda,∗8,∗13 M. Matsushita,∗10 R. Minakata,∗4

T. Motobayashi,∗1 T. Murakami,∗5 K. Muto,∗5 T. Nakamura,∗4 N. Nakatsuka,∗8 A. Navin,∗11 M. Nishimura,∗1

S. Ogoshi,∗4 J. Ohnishi,∗1 S. Sakaguchi,∗12 H. Sakurai,∗1 M. Sasano,∗1 H. Sato,∗1 Y. Satou,∗7 K. Sekiguchi,∗5

Y. Shimizu,∗1 T. Sumikama,∗5 Y. Wada,∗5 K. Yoneda,∗1 and J. Zenihiro∗1

The study of neutron-proton (np) correlations in nu-clei is very important to understand the nuclear struc-ture. Direct two-nucleon knockout reactions offer apowerful tool for quantitative measurements of the n-p correlations in N = Z nuclei.1,2) The measured in-clusive two-nucleon knockout cross sections3,4) showsignificant enhancement of np (T = 0 & 1) over nnand pp (T = 1) correlations in 12C. The shell-modelcalculation for the two-nucleon overlaps within the pshell can reproduce the inclusive cross sections for like-nucleon pair removal, but underestimates the np-pairremoval cross section by approximately a factor of t-wo.1) This discrepancy implies insufficient descriptionof the T = 0 np interactions in the shell-model wavefunctions. A recent calculation using the no-core shellmodel that exploits modern chiral effective field theo-ry NN+3N interactions2) suggests that the final-state-exclusive np-knockout cross sections from 12C to theT = 0 states can provide an immediate test of the npcorrelations (particularly in their T = 0 componen-t) and three-nucleon forces. To investigate the natureof these forces, we therefore measured γ-residue co-incidence to extract the final-state-exclusive np- andpp-removal cross sections from 12C to 10B and 10Be.The experiment was carried out at RIBF. The sec-

ondary 12C beam (presently not available as the pri-mary beam for SRC-use experiments) was produced byfragmentation of an 18O primary beam at 250 MeV/uusing a 5-mm thick Be target. The ions of interestwere selected using the BigRIPS fragment separator5)

by measuring the energy loss (∆E ) and time of flight(TOF) with plastic scintillators at the intermediate fo-ci F3 and F13. The incident angle and position of thebeam on a 1.879-g/cm2 thick Be target were deter-mined by two drift chambers, BDC1 and BDC2. Thetarget was surrounded by the DALI2 γ-ray spectrom-

∗1 RIKEN Nishina Center∗2 School of Physics and State Key Laboratory of Nuclear

Physics and Technology, Peking University∗3 Department of Physics, The University of Hong Kong∗4 Department of Physics, Tokyo Institute of Technology∗5 Department of Physics, Tohoku University∗6 LPC, Caen∗7 Department of Physics, Seoul National University∗8 Department of Physics, Kyoto University∗9 Department of Physics, The University of Tokyo∗10 CNS, The University of Tokyo∗11 GANIL, CEA/DSM-CNRS/IN2P3∗12 Department of Physics, Kyushu University∗13 CYRIC, Tohoku University

A/ZMass-to-Charge Ratio 1.6 1.8 2 2.2 2.4 2.6

ZC

harg

e N

umbe

r 3

4

5

6

7h2h2

1

10

210

B10

Be10

Fig. 1. Particle identification after the secondary target.

eter.6) One hundred and fifty-nine crystals of DAL-I2 were employed with an azimuthal angular coveragefrom 25◦ to 154◦. The mid-target energy of 12C wasapproximately 190 MeV/u. Reaction products weretransported to the SAMURAI spectrometer7) and i-dentified with the Bρ-∆E -TOF method. The mag-netic rigidity Bρ was determined from the measuredpositions at the forward drift chambers, FDC1 andFDC2. ∆E and TOF were measured by using the plas-tic scintillator hodoscopes, HODF and HODP. Fig. 1shows the particle identification of reaction residues.It should be noted that the reaction channels of inter-est were measured simultaneously because of the largeacceptance of SAMURAI.

The preliminary ratio of inclusive np- to pp-removalcross sections was obtained, which is consistent withthe previous result within errors.3) Currently, the γ-ray spectrum analysis is ongoing. Further, the partialcross sections will be extracted.

References1) E. Simpson and J. A. Tostevin: Phys. Rev. C 83, 014605

(2011).2) E. Simpson et al.: Phys. Rev. C 86, 054609 (2012).3) J. M. Kidd et al.: Phys. Rev. C 37, 2613 (1988).4) D. L. Olson et al.: Phys. Rev. C 28, 1602 (1983).5) T. Kubo et al.: Prog. Theor. Exp. Phys. 2012, 03C003

(2012).6) S. Takeuchi et al.: Nucl. Instr. Meth. A 763, 596 (2014).7) T. Kobayashi et al.: Nucl. Instr. Meth. B 317, 294

(2013).

Measurement of the 132Sn(p, n) reaction at 270 MeV/nucleon

M. Sasano,∗1 J. Yasuda,∗2 R.G.T. Zegers,∗3 H. Baba,∗1 W. Chao,∗1 M. Dozono,∗1 N. Fukuda,∗1 N. Inabe,∗1

T. Isobe,∗1 G. Jhang,∗1,13 D. Kamaeda,∗1 T. Kubo,∗1 M. Kurata-Nishimura,∗1 E. Milman,∗1 T. Motobayashi,∗1

H. Otsu,∗1 V. Panin, ∗1 W. Powell, ∗1 M. Sako, ∗1 H. Sato,∗1 Y. Shimizu,∗1 L. Stuhl,∗1 H. Suzuki,∗1 T. Suwat,∗1 H. Takeda,∗1 T. Uesaka,∗1 K. Yoneda,∗1 J. Zenihiro,∗1 T. Kobayashi,∗4 T. Sumikama,∗4 T. Tako,∗4

T. Nakamura,∗5 Y. Kondo,∗5 Y. Togano,∗5 M. Shikata,∗5 J. Tsubota,∗5 K. Yako,∗6 S. Shimoura,∗6 S. Ota,∗6

S. Kawase,∗6 Y. Kubota,∗6 M. Takaki,∗6 S. Michimasa,∗6 K. Kisamori,∗6 C.S. Lee,∗6 H. Tokieda,∗6

M. Kobayashi,∗6 S. Koyama,∗7 N. Kobayashi, ∗7 H. Sakai,∗8 T. Wakasa,∗2 S. Sakaguchi,∗2 A. Krasznahorkay,∗9

T. Murakami, ∗10 N. Nakatsuka, ∗10 M. Kaneko, ∗10 Y. Matsuda, ∗11 D. Mucher, ∗12 S. Reichert, ∗12 D. Bazin,∗3

and J.W. Lee∗13

Among the collective modes1), the Gamow-Teller(GT) giant resonance is an interesting excitation mode.It is a 0h̄ω excitation characterized by the quantum-number changes of orbital angular momentum (∆L =0), spin (∆S = 1), and isospin (∆T = 1), and in-duced by the transition operator στ . In the stablenuclei in medium or heavier mass regions (A > 50),the collectivity in this mode exhibits the GT giant res-onance (GTGR), which gives information that is crit-ically important for understanding the isovector partof the effective nucleon-nucleon interaction2) and thesymmetry potential of the equation of the state3).

The goal of the NP1306-SAMURAI17 experimentperformed in Spring 2014 was to extract the GT andspin-dipole (SD) transition strengths over a wide exci-tation range covering their giant resonances on the keydoubly magic nucleus 132Sn via the charge-exchange(p, n) reaction at 270 MeV/nucleon in inverse kine-matics. This is an essential step toward establishingcomprehensive theoretical models for nuclei situatedbetween 78Ni and 208Pb; at the same time, this is amilestone for extending the research on various phe-nomena in stable nuclei such as GT quenching, andnuclear weak processes of astrophysical interest, to theneutron-rich region far from the beta stability. An ex-perimental technique based on the missing mass spec-trocopy4,5) was employed to reconstruct the excitationenergy spectra for the reaction.

In the experiment, a secondary beam of 132Sn at270 MeV/nucleon was produced through an abrasion-fission reaction with a 345 MeV/nucleon primary beamof 238U. The resulting cocktail beam had a total inten-sity of 1.4×104 pps, containing 132Sn with a purity of45%. The particle identification (PID) was performed

∗1 RIKEN Nishina Center∗2 Department of Physics,Kyushu University∗3 NSCL Michigan State University∗4 Department of Physics, Tohoku University∗5 Tokyo Institute of Technology∗6 CNS, University of Tokyo∗7 University of Tokyo∗8 ULIC, RIKEN Nishina Center∗9 MTA, Atomki, Debrecen, Hungary∗10 Kyoto University∗11 Konan University∗12 Technical University Munich∗13 Department of Physics, Korea University

Fig. 1. Top view of the experimental setup around the

SAMURAI spectrometer.

on an event-by-event basis by measuring the energyloss in the ionization chamber at the F7 focal plane,and the magnetic rigidity and the time of flight of thebeam particles in the BigRIPS spectrometer.

Figure 1 shows a top view of the experimental setuparound the SAMURAI spectrometer6). The secondarybeam was impinged on a liquid hydrogen target7) be-fore the entrance of the SAMURAI magnet. The re-coil neutrons were detected by using the Wide-angleInverse-kinematics Neutron Detectors for SHARAQ(WINDS) surrounding the target. The PID of thereaction residues was performed with the SAMURAIspectrometer and the decay neutrons from the residueswere detected with the NEBULA. Detailed reports onthe WINDS setup, the PID analysis in the SAMURAIspectrometer, and the NEBULA DAQ based on a fastclear mode are given in other reports in the currentvolume of the APR. The analysis is in progress. Inpreliminary results, the kinetic curves correspondingto the (p, n) reaction are clearly observed; this indi-cates that the experiment worked as planned.

References1) M. N. Harakeh and A. M. van der Woude: Giant Reso-

nances (Oxford University Press, Oxford, 2001).2) S. Fracasso and G. Colo: Phys. Rev. C 72, 064310

(2005).3) P. Danielewicz: Nucl. Phys. A 727, 233 (2003).4) M. Sasano et al.: Phys. Rev. Lett. 107, 202501 (2011).5) M. Sasano et al.: Phys. Rev. C 86, 034324 (2012).6) T. Kobayashi et al.: Nucl. Inst. Meth. B 317, 294-304

(2013).7) M. Kurata-Nishimura et al.: RIKEN Accel. Prog. Rep.

45, 122 (2012).

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Ⅱ-1. Nuclear Physics RIKEN Accel. Prog. Rep. 48 (2015)RIKEN Accel. Prog. Rep. 48 (2015) Ⅱ-1. Nuclear Physics

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