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2004.06.08 dane2004. First Exclusive Measurement of the Non-Mesonic Weak Deacay of 12  C. Contents of talk n+n/n+p coincidence measurement  n / p ~ 0.40 ±0.09 (statistical error). Preliminary!!. Seoul national University. M.J.Kim.

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slide1

2004.06.08 dane2004

First ExclusiveMeasurement of the Non-Mesonic Weak Deacay of 12C

Contents of talk

n+n/n+p coincidence measurement

n/p~ 0.40±0.09(statistical error)

Preliminary!!

Seoul national University

M.J.Kim

KEK-PS E462/E508 Collaboration

e462 e508 collaboration
E462/E508 Collaboration

KEK, RIKEN, Seoul Univ., GSI,

Tohoku Univ., Osaka Univ., Univ. Tokyo

Osaka Elec. Comm. Univ. , Tokyo Inst. Tech.

S. Ajimura, K. Aoki, A. Banu, H. Bhang, S.Shin,T. Fukuda,

O. Hashimoto, J. I. Hwang, S. Kameoka, B. H. Kang,

E. H. Kim,J. H. Kim, M. J. Kim, T. Maruta, Y. Miura,

T. Nagae, S. N. Nakamura,

H. Noumi, S. Okada, Y. Okatasu, H. Outa, H. Park,

P. K. Saha, Y. Sato, M. Sekimoto, T. Takahashi,

H. Tamura, K. Tanida, A. Toyoda, K.Tsukada,

T. Watanabe, H. J. Yim

slide3

Purpose

Weak decay mode of  hypernucleus

Mesonic

q ~ 100MeV/c

Γπ_(Λ→ p + π-)

Γπ0(Λ→ n + π0 )

Γm

1/τHY =Γtot

Γp(Λ+ p→ n + p)

Γn(Λ+ n → n + n)

Non Mesonic(NMWD)

q ~ 400MeV/c

Γnm

Γ2N(ΛNN → NNN ) ?

Direct determination of the ratio !!!!

n/p

slide4

Status of n/p of 12C(until recently)

Theory

0.19

n/pexp >>n/pth

n/p ratio puzzle!

0.27

0.20

0.83

0.12

0.10

Problems in Experiment

1)high threshold

2) Large error bar

Problems in determination method of n/p ratio from data

1)model dependent

2) Effects of FSI and 2N process

Experiment

1.33±1.21/0.81

1.87±0.59±0.32/1.00

* FSI: Final State Interaction

slide5

Direct Measurement of the n /pratio

Select ΛN→NN events without FSI and 2N process effect

Top Detector

Angular correlation

( back-to-back, cosq<-0.8 )

Energy correlation

( energy sum ~ Q value~150MeV )

Nucleon

N

NMWD

N → NN

N

Ynp=Nnpx npx nx px (1-RFSI)np

Ynn=Nnnx nnx nx nx (1-RFSI)nn

By charge symmetry

(1-RFSI)np=(1-RFSI)nn

~ =

12LC g.s.

Bottom Detector

slide6

(KEK-PS K6 & SKS)

SETUP

Decay arm

+

Solid angle

Neutral: 26.5%

Charged : 10%

NT

p

K+

n

NT: 20cm×100cm×5cm

T3: 10cm×100cm×2cm

T2: 4cm×16cm×0.6cm

Charged particle:

・TOF (T2→T3)

・tracking(PDC)

Neutral particle:

・TOF (target→NT)

・T3 VETO

Active Target

beam

slide7

Excitation energy spectra for 12C(p+,K+)

12LC g.s.

quasi free

inclusive

11C + 

10.76MeV

Proton decay

11

9.21MeV

B+ p

w/ proton

11

B

8.1 MeV

6.3 MeV

w/ neutron

w/ n+p

2.5 MeV

0.0 MeV

12

C

w/ n+n

12

Level scheme of C

Excitation Energy(MeV)

11LB

slide8

Particle identification

Neutral particle

Charged particle

proton

5MeV< energy < 150MeV

Neutron

d

Constant

back ground

→ very small

1/

PID1 : total energy vs dE/dx

PID2 : total energy vs TOF

 (PID1+PID2) /

Energy resolution

~8MeV at ~75MeV

gated 12LC ground state

slide9

Coincidence Measurement

Angular Correlation

Energy sum

En +Ep

cos θ<-0.8

EN>30MeV

n + p

Number:109

cos θ<-0.8

En +En

EN>30MeV

n + n

Q value

~150

Number:33

MeV

cos θ

Estimated Contamination from - absorption

slide10

Estimation of Nnp,Nnn (Nnn/Nnp = 0.40±0.09)

MeasuredYnn,Ynp

Simulated coincide efficiency

EstimatedNnn,Nnp

np(Ep,n=65MeV)

Nnp=Ynp/np ~5677±572

cos θ<-0.8

EN>30MeV

Number:109

Event by event correction

Nnn=Ynn/nn~2267±437

cos θ<-0.8

nn(En,n=65MeV)

EN>30MeV

Number:33

Angular Correlation(cos )

θ

slide11

Coincidence Measurement(E462/E508)

Angular distribution

Energy sum distribution

Counts

n + p

s-shell

5

He

n + n

Q value

~ 153MeV

n + p

p-shell

12

C

n + n

cos θ

Estimated Contamination from - absorption

slide12

Results

5He (E462):0.45 ± 0.11 ± 0.04 (Final !!)

12C (E508):0.40 ± 0.09(statis.) (Preliminary !!)

n/p

12

5

C

He

Noumi et al.

Szymanski et al.

Sato et al.(1N)

Sato et al.(1N+2N)

Szymanski etal.

Kim et al.(1N)

OME

OME,DQ

OPE

OPE

E307

E307

E369

E508

E462

Theory(OPE)

Various Experiments

Theory(OME or DQ)

summary
Summary
  • The np- and nn-pairs from NMWD of 12C were observed successfully.

The energy sum of back-to-back np- and nn- pairs are approximately equal to the Q-values(~150MeV) of the NMWD.

N nN process were clearly identified !!

  • We got n/p ratio of 12C at cos <-0.8 and EN>30MeV .

n/p ~ Nnn/Nnp ~ 0.40 ±0.09(statis. ) (Preliminary!! )

(expected systematic error ~ ±0.04)

Consistent with recent theoretical calculations !!!!

θ

slide15

Experimental results

n/p

1.33±1.21/0.81

1.87±0.59±0.32/1.00

0.87±0.09±0.21(1N)

0.60±0.11/0.09±0.23/0.21(1N +2N)

0.51±0.15(1N)

slide16

Neutron and proton spectra from 12C

Neutron

N n,p/NMWD/10MeV

Proton

Nucleon energy

(MeV)