The Quenching of Nucleon Yields in the Nonmesonic Weak Decay of Λ Hypernuclei and the Three-body We

ak Interaction Process.

H. Bhang(Seoul National University)

for KEK-PS E462/E508 collaboration

HYP2006 conference Mainz, Germany Oct. 10-14, 2006

I. Decay Modes of NMWDII. Recent Developments on Γ n/Γ p and

III. Quenching of Nucleon Yield and the three-Body decay Process

Nonmesonic q~ 400 MeV/c

Weak Decay Modes of Λ Hypernuclei

Γ tot(=1/τ )

Γm

Γ nm

Γπ - ( Λ pπ - )

Γπ o ( Λ nπ o )

Γ p ( Λp np )

Γ n ( Λn nn )

Mesonic

q~ 100 MeV/c

Γ 2N (ΛNN nNN)

(1N)(2N)

3-Body Process

(3-Body)

- B-B weak interaction (ΔS=1)

- Long standing Γ n/Γ p Puzzle;

Γ n/Γ pexp >> Γ n/Γ p

th(OPE)

~ 1 ~0.1

2. Experimental Developments;

p n p,n singles spec np,nn pair no. ~ 1.0 ~0.5 ~0.5 ~ 0.5

E462(5ΛHe)/E508(12ΛC)

Recent Developments on Γ n/Γ p ratio

- Residual FSI effects

- No 2N NMWD assumed!!

Ambiguity

Sources!!

10 0.5 1.5

n / p

OPE

1. Recent Development of Γ n/Γ ptheory : 0.3 ~ 0.7

K

Coincidence Measurement (KEK-PS Coincidence Measurement (KEK-PS E462E462/E508)/E508)

π

SKS

Ep

En

π

θ

To exclude FSI effect and 3-body decay in Г n/ Г p and to identify 2N channel, Exclusive meas. of each decay channel.

Related presentations; 1. H. Outa (Plenary talk) 2. M. Kim ( poster session )

3. Maruta (this session)

K+

Nn / Np (E>60MeV)~ 2.00±0.09±0.14

Γ n/Γ p=0.58±0.06±0.08.

Nn / Np (60<E<110MeV) ~ 2.17±0.15±0.16

Γ n/Γ p=0.61±0.08±0.08.

Singles spectrum in NMWD

Okada et al., PLB 597 (2004) 249

(0.59)

(0.50)

1. Sharp peak in np pair(5ΛHe) at Q value.

FSI negligible in He.2. Broad spec in nn (5ΛHe). FSI? No. π - absorption or 2N? π - can not make it broad.

Seems 3B spectrum!!3. Ynp(C); FSI is significant.

4. Ynn(C); Even further degraded. Again points to 3B decay.

Esum = En + Ep Esum = En1 + En2

QQ

QQ

Coincidence Yields

(Esum)np=12(8), (Esum)nn=16(11) MeV

;E not enough to explain the broadening

2B

Pair energy sum (Esum) correlation

Esum=En+Ep

Esum=En+Ep

Esum=En+En

Esum=En+En

3B?

np pair nn pair

Back-to-back(bb) (cosθ≤ -0.8)

nbb nbb

bb

npnn / np = 0.45±0.11±0.03

B.Kang et al., Pys. Rev. Lett. 96 (2006) 062301

• back-to-back(bb) dominant

• Non-bb (nbb);

In np; few events.

In nn, more counts

NNN YNN/(Ynm•εNN)

Coincidence Yields : NNN Angular Correlation

Γ n/Γ p = 0.51±0.13±0.05 M. Kim et al., PLB 641 (2006) 28

- np ; bb dominant

- nn ; nbb enhancement

Nbb~Nnbb

- FSI corrected using pp

yields.

- Nnn/Nnp;2N effect

kinematically reduced

NN angular correlations

Angular

bb (cosθ≤ -.7)

bbnbb

cosθ Ynp Nnp Ynn Nnn Ypp Npp

bb 116.138±.01

443

.083±.014

8.005

±.002

nbb 12.060±.01

823

.083±.020

0

Now Γ n/Γ p ratio is well determined removing the ambiguities of

FSI and 2N.

Then what has been the reason of the Γ n/Γ p puzzle ??

1. Quenching of Singles Yields

Signatures of Three Body Processes

Compared to INC spectrum

(Nn+

Np)/

NM

WD

EN (MeV)

12ΛC

-Quenching of Nn+Np can not be explained by 1N-nmwd only.!!

- For 2N-nmwd, we adopted the kinematics of uniform phase space sharing of 3 nucleons

np2.0

0.10.5

0.5

0.1

2.0

2. Quenching of Pair Yields

Nnp(bb) Nnp(nbb) Nnn(bb) Nnn(nbb)

E508 0.138 ±0.01

4

0.060 ±0.018

0.083 ±0.01

4

0.083 ±0.014

INC (1N only)

0.229 0.084 0.117 0.045

INC (2N=0.4N

M)0.168 0.070 0.089 0.035

15 counts

8 counts

3. Enhancement of nn pair yields in nbb region

This model tends to produce 2 HE neutron and one LE proton. Then protons are often cut off at the threshold.

1. Enhancement of Nnn in nbb.

Assign it to Г 2N.

2. Estimation;

1) Nnp(nbb) all FSI eff.

Same FSI on Nnn

Г 2N ~ The residual Nnn

after FSI sub.

Г 2N ~0.180.14 Γ nm±±±

2) Similarly,

but using INC for FSI

Г 2N ~0.300.19 Γ nm

cosθ Ynp Nnp Ynn Nnn

bb 116.138±.01

443

.083±.014

nbb 12.060±.01

823

.083±.020

Nnbb/Nbb0.43±.01

41.00 ±.30

np pair nn pair

Reproduction of Singles and Coincidence yields with INC

Г n/ Г p=0.5

Г 2N=0.4 Г nm

Proton spectrum

Г n/ Г p=0.5

Г 2N=0.4 Г nm

Neutron spectrum

Summary

1.The coincidence exclusive measurements of each NMWD channel, Λnnn and Λpnp, accurately determined Г n/ Г p ~0.5 for 5

He and 12ΛC.

2.The underlying reason for the long-stood Γ n/Γ p puzzle.

The Quenching of nucleon yields.

3. The 3-body weak decay process, ie Γ 2n, provides a good mechanism to explain the quenching.

4. Both singles and coincidence yields indicate a fairly large Γ 2N comparable to Γ n, but with less than 2σ stat. significance.

5. Now the accurate measurement ofГ 2N becomes so important that we have to measure it before each determination ofГ n andГ p. J-PARC Proposal P18.

KEK, RIKEN, Seoul N.Univ., GSI,Tohoku Univ., Osaka Univ., Univ. Tokyo,

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

S. Ajimura, K. Aoki, A. Banu, H. Bhang, 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,

Y. Miyake, T. Nagae, M. Nakamura, 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

KEK-PS E462/508 KEK-PS E462/508 collaborationcollaboration

Extra Slides

No kinematic seperation With kinematic seperation

Methods

SinglesQuenching

NNN

Quenching

N2N;in Nnnnbb

Npn2N=0

N2NNNN

exp-NNNINC

Γ2N/ΓNM0.41 0.37 0.18±0.14* 0.30±0.19*

Simple Estimation of Г 2N

* Stat. error only.

No kinematic seperation With kinematic seperation

Methods

SinglesQuenching

NNN

Quenching

N2N;in Nnnnbb

Npn2N=0

N2NNNN

exp-NNNINC

Γ2N/ΓNM0.41 0.37 0.18±0.14* 0.30±0.19*

Rough Estimation of Γ2N

1. Consider the Nnpnbb all due to FSI. Then subtract the corresponding FSI amou

nt from Nnnnbb. The remainder would be N2N. This give us a kind of lower limit o

f Γ 2N which is about ~18% of Γ nm.

2. Use INC calculation result to estimate the FSI component in Nnpnbb. Then it wi

ll give ~30% of Γ nm.

* Stat. error only.

Nnp(bb) Nnp(nbb) Nnn(bb) Nnn(nbb)

E508 0.138 ±0.01

4

0.060 ±0.018

0.083 ±0.01

4

0.083 ±0.014

INC (1N only)

0.229 0.084 0.117 0.045

INC (2N=0.4N

M)0.168 0.070 0.089 0.035

2. Quenching of Pair Yields

np pair

nn pair

1. Quenching of Singles Yields

Signatures of Three Body Processes

Compared to INC spectrum

(Nn+

Np)/

NM

WD

EN (MeV)

12ΛC

Quenching of Nn+Np can not be explained without Г 2N.!!

For 2N, we adopted the kinematics of uniform phase space sharing of 3 nucleons.

np

σ NN 2 x σ NN