Nonmesonic weak decay of 5ΛHe and 12ΛC and

the effect of FSI on its observables

H. Bhang for KEK-PS SKS collaboration

(Seoul National University)

Dafne04 Conf. on Physics at Meson Factories

LNF, Frascati June 07~ 11, 2004

I. Issues / focus of NMWD II. Recent ExperimentsIII. Г n/ Г p, FSI and 2N contribution.

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

Nonmesonic

q~ 400 MeV/c

Weak Decay Modes of Λ Hypernuclei

Main focus of this talk

High momentum interaction

Γ 2N (ΛNN NNN)

(1N)(2N)

Non-Mesonic Weak Decay (NMWD) & Issues

1. B-B Weak Interaction ;

Λ + N -> N + N (ΔS=1 B-B Weak Interaction )

2. Long standing puzzle on : Γ n/Γ p (≡np ratio)

3. 2N NMWD: Predicted to be a significant component of NMWD, though not experimentally identified yet.

4. Asymmetry ; The relative phase concern of PC and PV part of NMWD interaction.

5. Final State Interaction : It seems one of the important elements to unde

rstand NMWD.

Hyp. Nuc.

Γnm Γn/Γp

BNL

5ΛHe 0.41±0.1

4.93±0.55

12ΛC 1,14±0.2 1.33±1.12/0.

81

KEK’95

12ΛC 0.89±0.1

81.87±0.91/1.

59

Status of Γn/Γp puzzle

Γ n/Γ pexp >> Γ n/Γ p

th(OPE)

~ 1 ~0.1

1. Γ n/Γ p Puzzle :

3. Recent Exp. Development:

p n p,n simultaneous p,n coinc.

~ 1.0 ~0.5 ~0.5 ~ 0.4

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

Np/d

ecay

where 2N ; ΛNN NNN.

Proton Energy spectrum

INC

Np/nm ~0.4

Ramos et al.

Λ+nn+nΛ+pn+p

Sato et al., PRC submitted

2N)(1N 0.230.11

(1N) 0.210.09

0.60

0.87

pΓnΓ

INC

Nn=0.69

Neutron Spectrum

Efficiency

Np =0.401. n yield is directly compared with th

at of p.

2.

3. Simple number counting givesPRC 68 (03) 065201

Λ+nn+nΛ+pn+p

1.730.40.6940MeV)(

pNnN

0.372

1p/NnN

pΓnΓ

- Assume 1N process only ; rn + rp = 1.

- The neutron (proton) number per NMWD

Nn=Yn/NnmΩnεn = (2rn+rp)f + rpg

Np=Yp/NnmΩpεp = rpf + (2rn+rp)g,

where f, g ; FSI effects.

Correction for Cross over recoil effects

0.51),(0.45-r

r1

ΓΓ

p

p

p

n

- Obtained model independently assuming 1N process. - The INC β value is used only for second order correction.

β=0.076

Γ n/Γ p = (0.45~0.51)+-0.15

pp

pp

p

n

r)r2(

rr2

NN

INC .11)-(.076f

gβ where

Г n/Г p ratio

E307/E369 : Г n/ Г p (12

ΛC)|1N = (0.45 ~0.51)± 0.14 (stat. only)

- Almost model independent.- This ratio agrees well with the most recent theoretical values (~.5)

In order to resolve the difficulties,• Exclusive measurements

• 5ΛHe E462

• 12ΛC E508

• final state int. • 2N induced NMWD.

However, ambiguities due to

p

n

π

K

Setup E462Setup E462/E508/E508(KEK-PS K6 beamline & SKS)

Solid angle: 26%9(T)+9(B)+8(S)%

θ

Neutron and Proton energy spectra of Neutron and Proton energy spectra of 55He and He and

1212CC

Nn / Np (E>60MeV)～ 2.00±0.09±0.14

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

135MeV

apply a simple relation n / p = (Nn / Np - 1) / 2

n / p ～ 0.5

To avoid suffering from FSI effect & ΛNN→NNN,

High energy threshold High energy threshold

n+pn+p

n+nn+n

Estimation of Nnn, Nnp (Nnn/Nnp=0.45±0.11±0.04)

measured

measured

N(nn-pair)/nn~1956

N(n+p)=90( -1.34)

N(n+n)=30(-4.38)

En,p>30MeV

Cos()<-0.8

Angular correlation cos()

-1 0 1-1 0 1 -1 0 1

- contamination

nn, np measured

N(np-pair)/np~4180

1000

Γ n/Γ p from Nn/Np & Nnn/Nnp

Simple counting of singles yields of n,p andcoincidence yeilds of nn, np pairs gives,

Nn/Np = 2•Г n/ Г p + 1,Nnn/Nnp ~ Г n/ Г p,

neglecting FSI and 2N.

Γ n/Γ p(Nn/Np) 0.59 (5ΛHe), 0.5 (12ΛC),

Γ n/Γ p(Nnn/Nnp) 0.45 (5ΛHe), 0.40 (12ΛC).

For the singles of E462/E508

5ΛHe (E462) Γ n/Γ p(5ΛHe) = 0.61 ± 0.081 ± 0.082.

12ΛC (E508) Γ n/Γ p(12

ΛC) = 0.58 ± 0.06 ± 0.08.

5ΛHe (E462) Γ n/Γ p(5ΛHe) = 0.61 ± 0.081 ± 0.082.

12ΛC (E508) Γ n/Γ p(12

ΛC) = 0.58 ± 0.06 ± 0.08.

Correction for Cross over recoil effects

Similiarly for the coincidence yields of 5ΛHe and 12ΛC (E462/E508),

β'n2rpr

β'prnrαnpNnnN

where β ’ is reduced β due to the

back-to-back selection.

5ΛHe (E462) Γ nn/Γ np(5ΛHe) = 0.43 ± 0.12 ± 0.044

12ΛC (E508) Γ nn/Γ np(12

ΛC) = 0.34 ± 0.13 ± 0.05.

5ΛHe (E462) Γ nn/Γ np(5ΛHe) = 0.43 ± 0.12 ± 0.044

12ΛC (E508) Γ nn/Γ np(12

ΛC) = 0.34 ± 0.13 ± 0.05.

5ΛHe : 0.61±0.081±0.082 (E462)

12ΛC : 0.58±0.06± 0.08 (E508)

: (0.45~0.51)±0.15 ( E307/E369)

Γ n/Γ p Status

10 0.5 1.5

n / p

Exp.

OPE

OME, DQ model

5ΛHe : 0.43 ±0.12 ± 0.044±(E462)

12ΛC : 0.34 ±0.13 ± 0.05 (E508)

Singles

Coincidence

Summary1. I have discussed the recent experimental results on NMWD of Λ hypernuclei

and the effects of FSI on the Γ n/Γ p.

2. A series of experiments have been done at KEK-PS, the decay particle spectra of n and p (Nn, Np) and the exclusive coincidence pair yields (Nnn, Nnp) of NMWD

3. The ratios of singles yields of n/p and coincidence yeilds of nn/np gives Γ n/Γ

p values which well supports the recent theoretical ratios.

4. The difference of Γ n/Γ p values from singles yields of n/p and coincidence yeilds of nn/np is interpretted as 2N contribution. This probably is the first experimental indication of 2N process.

It is expected that the 2N contribution now can be extracted from the coincidence data.

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

Osaka Elec. Comm. Univ.G , 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 OHPs

Neutron and Proton energy spectra of Neutron and Proton energy spectra of 55He and He and

1212CC

Nn / Np (E>60MeV)～ 2.00±0.09±0.14

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

5He → n + : Q ～

135MeV (rate : 0.049±0.01-)

135MeV

apply upper energy limit of 110MeV !

apply a simple relation n / p = (Nn / Np - 1) / 2

n / p ～ 0.5

To avoid suffering from FSI effect & ΛNN→NNN,

High energy threshold High energy threshold

Corrected proton energy loss inside the target !!

Neutron and ProtonNeutron and Proton Energy spectra of Energy spectra of 55ΛΛHeHe and and

1212ΛΛCC

Nn / Np (E>60MeV) ~ 2.17±0.15±0.16

Neutron

Proton Neutron Proton

Nn / Np (E>60MeV) ~ 2.00±0.09±0.14

For the singles of E462/E508

pp

pp

p

n

r)r2(

rr2

NN

where α=2.00 (5ΛHe), 2.17 (12ΛC)

5ΛHe (E462) Γ n/Γ p(5ΛHe) = 0.61 ± 0.081 ± 0.082.

12ΛC (E508) Γ n/Γ p(12

ΛC) = 0.58 ± 0.06 ± 0.08.

5ΛHe (E462) Γ n/Γ p(5ΛHe) = 0.61 ± 0.081 ± 0.082.

12ΛC (E508) Γ n/Γ p(12

ΛC) = 0.58 ± 0.06 ± 0.08.

β=0.041

Correction for Cross over recoil effects

Similiarly for the coincidence yields of 5ΛHe and 12ΛC (E462/E508),

β'n2rpr

β'prnrαnpNnnN

5ΛHe (E462) Γ nn/Γ np(5ΛHe) = 0.43 ± 0.12 ± 0.044

12ΛC (E508) Γ nn/Γ np(12

ΛC) = 0.34 ± 0.13 ± 0.05.

5ΛHe (E462) Γ nn/Γ np(5ΛHe) = 0.43 ± 0.12 ± 0.044

12ΛC (E508) Γ nn/Γ np(12

ΛC) = 0.34 ± 0.13 ± 0.05.

where β ’ is reduce β due to the back-to-back selection.

Correction for Cross over recoil effects

Similiarly for the coincidence yields of 5ΛHe and 12ΛC (E462/E508),

β'n2rpr

β'prnrαnpNnnN

5ΛHe (E462) Γ nn/Γ np(5ΛHe) = 0.43 ± 0.12 ± 0.044

12ΛC (E508) Γ nn/Γ np(12

ΛC) = 0.34 ± 0.13 ± 0.05.

5ΛHe (E462) Γ nn/Γ np(5ΛHe) = 0.43 ± 0.12 ± 0.044

12ΛC (E508) Γ nn/Γ np(12

ΛC) = 0.34 ± 0.13 ± 0.05.

where β ’ is reduce β due to the back-to-back selection.

Correction for Cross over recoil effects

5ΛHe : 0.61±0.081±0.082 (E462)

12ΛC : 0.58±0.06± 0.08 (E508)

: (0.45~0.51)±0.15 ( E307/E369)

Γ n/Γ p Status

10 0.5 1.5

n / p

Exp.

OPE

OME, DQ model

5ΛHe : 0.45±0.11±0.04 (E462)

12ΛC : 0.40±0.09 (E508)

Singles

Coincidence

CONTENTS

I. Issues / focus of Nonmesonic Weak Decay (NMWD)

II. Recent Experiments1. Singles meas. ; Nn and Np; (KEK-PS E307 /E369)

2. Coincidence meas. : Nnn and Nnp (E462/E508)

III. Г n/ Г p and Final State Interaction 1. Effects of FSI onГ n/ Г p

2. 2N signature

IV. Summary

Taking the ratios of singles yields of n/p and coincidence yeilds of nn/np give Γn/Γp different values whose differce is interpreted as 2N contribution,

Γn/Γp (Nn/Np) 0.61(5He), 0.58(12C),Γn/Γp (Nnn/Nnp) 0.43(5He), 0.34(12C).

4. Showed that 2N component can be resolved from coincidence data. For the extraction of 2N contribution, one need FSI model calculation but only for the second order effect.

5. Pinning the The direct comparison of the spectra gave the Γn/Γp ratio close to 0.5.

The coincidence exclusive measurements of NMWD produced the results on NMWD quite free from FSI and 2N contribution. The results show the Γn/Γp ratio ~0.4.

5. As long as Γn/Γp ratio concerned, the experimental and theoretical ratios now well agree to each other. However, αnm remains inconsistent between those of experiment and theory.

Therefore,

Where

Γ n/Γ p = (0.45~0.51)±0.15

• Obtained model independently assuming 1N process and fn=fp.

• The INC β value is used only for second order correction.

HYP03 Conf.

1.73αr)βr(2

βrr2

NN

pp

pp

p

n

0.51).-0.45r

r1

ΓΓ

.11)-.076fg

β

p

p

p

n (

(

INC0.076

INC calculation

Theory: - 0.6 ～ - 0.7

Preliminary

NM=0.07±0.08p -0.00+0.08st

atis

tical

conta

mi

Asymmetry parameter of 5ΛHe (E462)

Preliminary

Blue : 12C : NM = -0.44 ± 0.32

Red : 11B : NM = 0.11 ± 0.44

Theory: - 0.6 ～ - 0.7

p

Asymmetry parameter of 12ΛC,11

ΛB (E508)

+0.08+0.00NM=-0.24±0.26

stat

istic

al

conta

mi

Nhyp Γn/Γp

sas02 5ΛHe 0.70

Ito02 5ΛHe 0.39

Gar03 5ΛHe 0.46

Ose01 12ΛC 0.53

Ito03 12ΛC 0.57

Gar03 12ΛC 0.34

Nhyp Γn/Γp

BNL5ΛHe .93±0.55

12ΛC 1.33±1.12/0.81

KEK’95 12ΛC 1.87±0.91/1.59

KEK(Sat02) 12

ΛC0.87±0.09±0.21 (1N)

0.60±0.11±0.23 (1N+2N)

KEK (Kim03) 12ΛC (0.45~0.51)±0.14

(1N)

E462 (Inclusive)

5ΛHe (0.66~0.69)±0.12 ( 1N)

E508 (Inclusive)

12ΛC (0.49~0.55)±0.10 ( 1N)

Th

eory

Exp

erim

en

t

HYP03 Conf.

Current Status of Γ n/Γ p