Nonmesonic weak decay of 5He and 12C and the effect of FSI on its observables

1
Nonmesonic weak decay of 5?He and 12?C 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
Experiments III. ?n/?p, FSI and 2N contribution.
2
Weak Decay Modes of ? Hypernuclei
Mesonic q 100 MeV/c
Gp- ( ? ? pp- ) Gpo ( ? ? npo )
Gm Gnm
Gtot(1/t)
Gp ( ?p ? np ) Gn ( ?n ? nn )
Nonmesonic q 400 MeV/c
(1N)
(2N)
G2N (?NN? NNN)
High momentum interaction
Main focus of this talk
3

• Non-Mesonic Weak Decay (NMWD) Issues
• 1. B-B Weak Interaction
• ? N -gt N N (?S1 B-B Weak Interaction )
• 2. Long standing puzzle on Gn/Gp (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 understand NMWD.

4
Status of Gn/Gp puzzle
1. Gn/Gp Puzzle
Gn/Gpexp gtgt Gn/Gpth(OPE) 1 0.1
2. Recent Development of Gn/Gptheory 0.3 0.7
3. Recent Exp. Development p n
p,n simultaneous p,n coinc. 1.0
0.5 0.5
0.4
5
?n?nn ?p?np
Proton Energy spectrum
Np/nm 0.4
INC
INC
Np/decay
Ramos et al.
Sato et al., PRC submitted
where 2N ?NN ? NNN.
6
Neutron Spectrum
Efficiency
Nn0.69

• n yield is directly compared with that of p.
• 3. Simple number counting gives

Np 0.40
PRC 68 (03) 065201
?n?nn ?p?np
7
Correction for Cross over recoil effects
- Assume 1N process only rn rp 1. - The
neutron (proton) number per NMWD NnYn/NnmOnen
(2rnrp)f rpg NpYp/NnmOpep rpf
(2rnrp)g, where f, g FSI effects.
? Gn/Gp (0.450.51)-0.15
- Obtained model independently assuming 1N
process. - The INC ß value is used only for
second order correction.
8
?n/?p ratio

•  E307/E369
• ?n/?p (12?C)1N (0.45 0.51) 0.14 (stat.
  only)

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

However, ambiguities due to

• In order to resolve the difficulties,
• Exclusive measurements
• 5?He ? E462
• 12?C ? E508

final state int. 2N induced NMWD.
9
Setup E462/E508
(KEK-PS K6 beamline SKS)
Solid angle 26 9(T)9(B)8(S)
p
p
n
K
10
Neutron and Proton energy spectra of 5LHe and
12LC
To avoid suffering from FSI effect ?NN?NNN,
High energy threshold
Nn / Np (60ltElt110MeV) 2.170.150.16
135MeV
Nn / Np (Egt60MeV) 2.000.090.14
apply a simple relation Gn / Gp (Nn / Np -
1) / 2 ? Gn / Gp 0.5
11
Estimation of Nnn, Nnp (Nnn/Nnp0.450.110.04)
En,pgt30MeV
N(np-pair)/enp 4180
Cos(q)lt-0.8
1000
N(np)90( -1.34)
measured
np
N(nn-pair)/enn 1956
N(nn)30(-4.38)
measured
nn
p- contamination
-1
0
1
-1
0
1
-1
1
0
nn, np measured
Angular correlation cos(q)
12
(No Transcript)
13
Gn/Gp from Nn/Np Nnn/Nnp
Simple counting of singles yields of n,p
and coincidence yeilds of nn, np pairs gives,
Nn/Np 2?n/?p 1, Nnn/Nnp ?n/?p,
neglecting FSI and 2N.
Gn/Gp(Nn/Np) ? 0.59 (5?He), 0.5
(12?C), Gn/Gp(Nnn/Nnp) ? 0.45 (5?He), 0.40
(12?C).
14
Correction for Cross over recoil effects
For the singles of E462/E508
5?He (E462) ? Gn/Gp(5?He) 0.61 0.081
0.082. 12?C (E508) ? Gn/Gp(12?C) 0.58 0.06
0.08.
Similiarly for the coincidence yields of 5?He and
12?C (E462/E508),
where ß is reduced ß due to the back-to-back
selection.
5?He (E462) ? Gnn/Gnp(5?He) 0.43 0.12
0.044 12?C (E508) ? Gnn/Gnp(12?C) 0.34 0.13
0.05.
15
Gn/Gp Status
OME, DQ model
OPE
Gn / Gp
1.5
0.5
1
0
Exp.
Singles
5?He 0.610.0810.082 (E462) 12?C
0.580.060.08 (E508) (0.450.51)0.15
(E307/E369)
5?He 0.43 0.12 0.044(E462) 12?C 0.34 0.13
0.05 (E508)
Coincidence
16
Summary

• I have discussed the recent experimental results
  on NMWD of ? hypernuclei and the effects of FSI
  on the Gn/Gp.
• 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 Gn/Gp values
  which well supports the recent theoretical
  ratios.
• 4. The difference of Gn/Gp 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.

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KEK-PS E462/508 collaboration
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
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Extra OHPs
19
Neutron and Proton energy spectra of 5LHe and
12LC
To avoid suffering from FSI effect ?NN?NNN,
High energy threshold
Nn / Np (60ltElt110MeV) 2.170.150.16
135MeV
5LHe ? n a Q135MeV (rate
0.0490.01Gp-)
apply upper energy limit of 110MeV !
Nn / Np (Egt60MeV) 2.000.090.14
apply a simple relation Gn / Gp (Nn / Np -
1) / 2 ? Gn / Gp 0.5
Corrected proton energy loss inside the target !!
20
Neutron and Proton Energy spectra of 5?He and
12?C
Nn / Np (Egt60MeV) 2.170.150.16
Nn / Np (Egt60MeV) 2.000.090.14
21
Correction for Cross over recoil effects
For the singles of E462/E508
ß0.041
where a2.00 (5?He), 2.17 (12?C)
5?He (E462) ? Gn/Gp(5?He) 0.61 0.081
0.082. 12?C (E508) ? Gn/Gp(12?C) 0.58 0.06
0.08.
22
Correction for Cross over recoil effects
Similiarly for the coincidence yields of 5?He and
12?C (E462/E508),
where ß is reduce ß due to the back-to-back
selection.
5?He (E462) ? Gnn/Gnp(5?He) 0.43 0.12
0.044 12?C (E508) ? Gnn/Gnp(12?C) 0.34 0.13
0.05.
23
Correction for Cross over recoil effects
Similiarly for the coincidence yields of 5?He and
12?C (E462/E508),
where ß is reduce ß due to the back-to-back
selection.
5?He (E462) ? Gnn/Gnp(5?He) 0.43 0.12
0.044 12?C (E508) ? Gnn/Gnp(12?C) 0.34 0.13
0.05.
24
Gn/Gp Status
OME, DQ model
OPE
Gn / Gp
1.5
0.5
1
0
Exp.
Singles
5?He 0.610.0810.082 (E462) 12?C
0.580.060.08 (E508) (0.450.51)0.15
(E307/E369)
5?He 0.450.110.04 (E462) 12?C 0.400.09
(E508)
Coincidence
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CONTENTS

• I. Issues / focus of Nonmesonic Weak Decay
  (NMWD)
• II. Recent Experiments
• 1. Singles meas. Nn and Np (KEK-PS E307
  /E369)
• 2. Coincidence meas. Nnn and Nnp
  (E462/E508)
• III. ?n/?p and Final State Interaction
• 1. Effects of FSI on?n/?p
• 2. 2N signature
• IV. Summary

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Taking the ratios of singles yields of n/p and
coincidence yeilds of nn/np give Gn/Gp different
values whose differce is interpreted as 2N
contribution, Gn/Gp (Nn/Np) ? 0.61(5He),
0.58(12C), Gn/Gp (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 Gn/Gp 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 Gn/Gp
ratio 0.4. 5. As long as Gn/Gp ratio concerned,
the experimental and theoretical ratios now well
agree to each other. However, anm remains
inconsistent between those of experiment and
theory.
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INC calculation

• Therefore,
• Where
• ? Gn/Gp (0.450.51)0.15
• Obtained model independently assuming 1N process
  and fnfp.
• The INC ß value is used only for second order
  correction.

0.076
HYP03 Conf.
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Asymmetry parameter of 5?He (E462)
Preliminary
p contami
statistical
0.08
aNM0.070.08
p
-0.00
29
Asymmetry parameter of 12?C,11?B (E508)
p contami
Preliminary
statistical
0.08
aNM-0.240.26
p
0.00
30
Current Status of Gn/Gp
Theory
Experiment
HYP03 Conf.