Study of two-nucleon correlation in 6He and 6Li

Toshimi Suda RIKEN

RIKEN : Ngyen T. Khai, A. Yoshida, T. Ohnishi, H. Takeda, I. Tanihata,KEK: S. Ishimoto, S. SuzukiNiigata Univ.: T. IzumikawaSaitama Univ. : K. Sugawara, S. Nakajima, K. Ogata, K. Kobayashi, T. SuzukiTsukuba Univ. : A. Ozawa, T. Yasuno, A. ChibaOsaka Univ. : Y. TakahashiHanoi Univ. : Le H. Khiem, Pham. Q. Hung

6He + p -> n + d + 4He6Li + p -> p + d + 4He

Dec. 19~ 23, 2004

6He

α

n n

α

p n

6Li

direct measurement of the relative momentum distributionfor correlated two nucleons inside 6He and 6Li

6He : α ＋ 2 n 　　　 (31S0)　　 6Li : α ＋ pn (13S1)

two nucleons, having different quantum numbers, are subjectto be studied.

Experimental goal

Two-nucleon system (pn) in 6Li• Example : momentum distribution and form factor of the “deuteron” inside 6Li

– 6Li(e,e’d) under quasi-elastic kinematics (~q2/2Md)• Momentum distribution |(pm)|2

• Form factor 　： size of the “deuteron” in 6Li

Momentum distribution （ σ~34 MeV/c) “d” in 6Li has similar size as free deuteron.

free deuteron€

d6σ

dpe dpd

= Kσ ed (q)φ(pm )2

NIKHEF exp.NPA578(‘94)93.

d

Pm

α-Pm

e’q

Di-neutron in 6He

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)– 13S1+ 13D1

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

0 200 400 600

( / )p MeV c

ρ( )p

-D state

-S state

6Li : + (pn) 6He: + (nn)

•Two nucleons inside a nucleus–T=1 pair is also possible–nn, pp pairs

•T=1 leads S=0, L=0, J=0 •31S0, 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

1

10

100

0 50 100 150

dσ/dΩ ( / )mb sr

scattering angle in CM

+ p d elastic scattering at Ed=140 MeV

p

d

d

p

exchange mechanism

K. Sekiguchi et al.,PRC 65,034003,2002

€

dσ

dΩ∝ ρ( p) ⋅ F(Δp)

2

PWIA

€

p =1

3p0

€

Δp = p0 −1

3p0 =

2

3p0

p0 1/3*p04/3*p0

proton deuteron proton deuteron

p0

1/3*p0

Momentum distribution

Form factor

nn in 6He, 　 pn in 6Li• 6He and 6Li are well described in NN+ in the cluster picture　

• ERI = 70 (110) MeV/u– Proton momentum:　　p0 = 370 (466) MeV/c/u– Accessed relative momentum between two nucleons

1/3*p0 ~ 120 (160) MeV/c

6He

α

n n

α

p n

6Li

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

0 200 400 600

( / )p MeV c

ρ( )p

-D state

-S state

RIBF

RIPS 実験

Qausi-deuteron(di-neutron) model

€

d2σ

dΩdE~ d3Pd F(Pd )∫ dσ

dΩ*

⎡ ⎣ ⎢

⎤ ⎦ ⎥p +d

Jtot

F(Pd) : Mometum distribution of deuteron (di-neutron)dσ/dΩ : p+d elastic cross section in CMJtot : Jacobian

At backward scattering where nucleon exchange process dominates

€

dσ

dΩ*

⎡ ⎣ ⎢

⎤ ⎦ ⎥p+'nn'

~ 2 ⋅dσ

dΩ*

⎡ ⎣ ⎢

⎤ ⎦ ⎥p +'d '

assuming the same radial wave function to that of deuteron

Simulation : p+d scattering in the inverse kinematics

P+d for Ed = 70MeV/u

0

20

40

60

80

100

0 50 100 150 200

θn [ ]deg

[ ]En MeV

0

10

20

30

40

0 50 100 150

θd [ ]deg

[ ]Ed MeV

180

150

120

90

6030

0180150

12090

60

300 proton deutron

0

20

40

60

80

100

0 50 100 150 200

θn [ ]deg

[ ]En MeV

0

10

20

30

40

0 50 100 150

θd [ ]deg

[ ]Ed MeV

proton deuteron

Backward scattering （ θCM≥130° ）　　 θp≤30°, Ep≥90 MeV　　 θd≤30°, 20≤Ed≤40 MeV

“deuteron” in 6Li （’ 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 6He and 6Li

• To measure : “backward” scattering cross section between the 2N system in nuclei and a target proton.

6Li

p n

α

p

αspectator

p

d

p,d,α

n

α

n6He

p

αspectator

n

d

n,d,α

“pn” in 6Li

“nn” in 6He　　 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 collimators10mmTransmission ~ 75%

SHT3mmt

deuteron detector10 strips x 2 layersΔθd =±2º

Neutron (proton) detector 20 cm thick in total

range counter

MWPC

CPV

From downstream

deuteron

deuteron

n(p)-detector

Solid Hydrogen Target

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-0.02

0

0.02

0.04

0.06

0.08

0.1

-10 0 10 20 30 40

SHT target shape measured by Laser

X (mm)

~350 μm

(30 )SHT mm

target cell

= 1 /10conversion mVμm resolutionΔ = 10 L μm

target cell

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Experiment (Oct.19 ~ 23)

• Primary beam : 12C 92 MeV/u• Secondary beam : 6He, 6Li 70 MeV/u• Beam intensity : ~ 105 Hz• 5º ≤ θd ≤ 30º, Δθd = ±2º

• 5º ≤ θn ≤ 30º

• |θ| ≤ 4º

• 120º ≤ θCM ≤ 180º, ΔθCM ~ 5º• Acceptance ~ 13%

Yield estimation

• p+d cross section （σ (p+”nn”) ~ 2 σ(p+”pn”))• Nt : 3 mmt solid hydrogen target

• Nbeam : 105 /sec

• accept. : ~13% (estimated by Monte Carlo)– The 2N momentum distribution （ σ=62 MeV/c)

• neutron : ~10% (for “nn”+p-> n +d ）

€

Yield = σ Lab. ⋅N t ⋅Nbeam ⋅εaccept. ⋅εneutron

70 MeV/u 110 MeV/u

6He 0.19 Hz 0.05 Hz6Li 1.9 Hz 0.5 Hz

Quick look of the experimental data

Secondary beam profile at MWPC

FWHM ~ 2 cm

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Particle identification

in the range counter

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6Li

4He

3He

3H,d,p

Events having

• low energy particle in the deuteron• large energy deposit in the n(p) detector

6Li + p => d + p + 4He

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Range counter4He !!

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MWPC

6Lideuteron detector

Neutron (proton) detector

range counter

MWPC

CPV