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The Quenching of Nucleon Yields in the Nonmesonic Weak Decay of Λ Hypernuclei and the Three-body Weak 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 NMWD - PowerPoint PPT Presentation
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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
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