Study of two-nucleon correlation in 6 He and 6 Li Toshimi Suda RIKEN RIKEN : Ngyen T. Khai, A. Yoshida, T. Ohnishi, H. Takeda, I. Tanihata, KEK: S. Ishimoto, S. Suzuki Niigata Univ.: T. Izumikawa Saitama Univ. : K. Sugawara, S. Nakajima, K. Ogata, K. Kobayashi, T. Suzuki Tsukuba Univ. : A. Ozawa, T. Yasuno, A. Chiba Osaka Univ. : Y. Takahashi Hanoi Univ. : Le H. Khiem, Pham. Q. Hung 6 He + p -> n + d + 4 He 6 Li + p -> p + d + 4 He Dec. 19~ 23, 2004

6 He α nn α pn 6 Li direct measurement of the relative momentum distribution for correlated two nucleons inside 6 He and 6 Li 6 He : α ＋ 2 n ( 31 S 0 ) 6 Li : α ＋ pn ( 13 S 1 ) two nucleons, having different quantum numbers, are subject to be studied. Experimental goal

Two-nucleon system (pn) in 6 Li Example : momentum distribution and form factor of the “deuteron” inside 6 Li – 6 Li(e,e’d)  under quasi-elastic kinematics (  ~q 2 /2M d ) Momentum distribution |  (p m )| 2 Form factor ： size of the “deuteron” in 6 Li Momentum distribution （ σ~34 MeV/c) “d” in 6 Li has similar size as free deuteron. free deuteron NIKHEF exp. NPA578(‘94)93. d PmPm α -P m e’ q

Di-neutron in 6 He di-neutron PRL 82(‘99)4996.

Relative momentum distribution between nucleons. Nucleon momentum distribution in deuteron –S, D wave orignated from the central and tensor forces –T=0,S=1,J=1 (L=0,2) – 13 S D 1 6 Li :  + (pn) 6 He:  + (nn) Two nucleons inside a nucleus –T=1 pair is also possible –nn, pp pairs T=1 leads S=0, L=0, J=0 31 S 0, having no tensor contribution

Proton+deuteron elastic scattering the backward elastic scattering : nucleon-exchange mechanism –The cross section is sensitive to the initial momentum of nucleon inside –The nucleon momentum distribution from the p+d backward scattering K. Sekiguchi et al., PRC 65,034003,2002 PWIA p0p0 1/3*p 0 4/3*p 0 proton deuteron protondeuteron p0p0 1/3*p 0 Momentum distribution Form factor

nn in 6 He, pn in 6 Li 6 He and 6 Li are well described in NN+  in the cluster picture E RI = 70 (110) MeV/u –Proton momentum: p 0 = 370 (466) MeV/c/u –Accessed relative momentum between two nucleons 1/3*p 0 ~ 120 (160) MeV/c 6 He α nn α pn 6 Li RIBF RIPS 実験

Qausi-deuteron(di-neutron) model F(P d ) : Mometum distribution of deuteron (di-neutron) d  /d  : p+d elastic cross section in CM J tot : Jacobian At backward scattering where nucleon exchange process dominates assuming the same radial wave function to that of deuteron

Simulation : p+d scattering in the inverse kinematics P+d for E d = 70MeV/u protondeutron protondeuteron Backward scattering （ θ CM ≥130° ） θp≤30°, Ep≥90 MeV θd≤30°, 20≤Ed≤40 MeV “ deuteron ” in 6 Li （ ’ d ’ +p->d+p) The kinematics for 6He ( ’ nn ’ +p->d+n) is similar

An experiment to study the relative momentum distribution of two nucleons inside 6 He and 6 Li To measure : “backward” scattering cross section between the 2N system in nuclei and a target proton. 6 Li p n α p α spectator p d p,d,αp,d,α n α n 6 He p α spectator n d n,d,α “pn” in 6 Li “nn” in 6 He θn≤30°, En ≥90 MeV θd≤30°, 20≤Ed≤40 MeV θp≤30°, Ep ≥90 MeV θd≤30°, 20≤Ed≤40 MeV

act. colli. SHT D-det. n(p)-det. MWPC range counter active collimators 10mm  Transmission ~ 75% SHT 3mmt deuteron detector 10 strips x 2 layers  d =±2º Neutron (proton) detector 20 cm thick in total range counter MWPC CPV

From downstream deuteron n(p)-detector

Solid Hydrogen Target

Experiment (Oct.19 ~ 23) Primary beam : 12 C 92 MeV/u Secondary beam : 6 He, 6 Li 70 MeV/u Beam intensity : ~ 10 5 Hz 5º ≤  d ≤ 30º,  d = ±2º 5º ≤  n ≤ 30º |   | ≤ 4º 120º ≤  CM ≤ 180º,  CM ~ 5º Acceptance ~ 13%

Yield estimation p+d cross section （  (p+”nn”) ~ 2  (p+”pn”)) N t : 3 mmt solid hydrogen target N beam : 10 5 /sec  accept. : ~13% (estimated by Monte Carlo) –The 2N momentum distribution （ σ=62 MeV/c)  neutron : ~10% (for “nn”+p-> n +d ）

Quick look of the experimental data Secondary beam profile at MWPC FWHM ~ 2 cm P article identification in the range counter 6 Li 4 He 3 He 3H,d,p

Events having low energy particle in the deuteron large energy deposit in the n(p) detector 6 Li + p => d + p + 4 He Range counter 4 He !! MWPC 6 Li deuteron detector Neutron (proton) detector range counter MWPC CPV