weak decay of 5 Λ he and 12 Λ c : experimental results
DESCRIPTION
10. Oct. 2006 HYP2006(Mainz). 1. Weak decay mode of L hypernucleus. Γ π _ ( L → p + π - ) Γ π 0 ( L → n + π 0 ). Mesonic q ~ 100MeV/c. Γ m. 1/ t HY =Γ tot. Γ p ( L +“ p”→ n + p ) Γ n ( L +“ n”→ n + n ) Γ 2N (ΛNN →NNN). Non-Mesonic ( NMWD ) q ~ 400MeV/c. Γ nm. - PowerPoint PPT PresentationTRANSCRIPT
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Weak decay of 5ΛHe and 12
ΛC : experimental results
RIKEN H. OutaRIKEN H. Outa
10. Oct. 2006 HYP2006(Mainz)
for KEK-PS E462 / E508 collaborationsOsaka Univ.a, KEKb, GSIc, Seoul Univ.d, Tohoku Univ.e,
Univ.of Tokyof, Tokyo Inst. Tech.g, KRISSh, RIKENi
S. Ajimuraa, K.Aokib, A.Banuc, H. C. Bhangd, T. Fukudab,O. Hashimotoe, J. I. Hwangd, S. Kameokae, B. H. Kangd, E. H. Kimd, J. H. Kimd, M. J. Kimd, T. Marutaf, Y. Miurae, Y. Miyakea, T. Nagaeb, M. Nakamuraf,
S. N. Nakamurae,H. Noumib, S. Okadag, Y. Okayasue, H. Outab, H. Parkh,P. K. Sahab, Y. Satob, M. Sekimotob, T. Takahashie,H. Tamurae, K. Tanidai, A. Toyodab, K. Tsukadae,T. Watanabee, H. J. Yimd
ΓΓππ__ (→ p + π - )
ΓΓππ00 ( → n + π 0 )
ΓΓpp ( +“ p”→ n + p )ΓΓnn ( +“ n”→ n + n )Γ2N (ΛNN →NNN)
Mesonic q ~ 100MeV/c
Non-Mesonic(NMWD) q ~ 400MeV/c
1/HY =Γtot
Γm
Γnm
Weak decay mode of Weak decay mode of hypernucleus hypernucleus
Study of the mechanism of baryon-baryon weak interaction
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Contents of the present talkContents of the present talkΓ(Λn→nn)/Γ(Λp→np) ratio n/p spectra from A=5,12 S. Okada et al. PLB 597 (2004) 249-256 A= 5 B.H. Kang et al. PRL 96 (2006) 062301 A=12 M.J. Kim et al. PLB 641 (2006) 28 [ M. Kim, poster session ] Asymmetry parameter T. Maruta et al. nucl-ex/0509016 [ T.Maruta, parallel session A2] Mesonic & non-mesonic decay widths [ S. Okada, poster session ] S. Kameoka et al. Nucl. Phys. A754 (2005) 173c-177c S. Okada et al. Nucl. Phys. A754 (2005) 178c-183c Two nucleon-induced NMWD (ΛNN→NNN) [H.Bhang, parallel session A2]
ΓΓππ__ (→ p + π - )
ΓΓππ00 ( → n + π 0 )
ΓΓpp ( +“ p”→ n + p )ΓΓnn ( +“ n”→ n + n )Γ2N (ΛNN →NNN)
Mesonic q ~ 100MeV/c
Non-Mesonic(NMWD) q ~ 400MeV/c
1/HY =Γtot
Γm
Γnm
Weak decay mode of Weak decay mode of hypernucleus hypernucleus
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10 0.5 1.5n / p
The
oret
ical
N N
NΛ
Direct Quark mechanism
Meson Exchangemechanism
Λ N
NN
π,K,η,ρ,ω,K*
0.93±0.55 (Szymanski et al.)Exp. (for 5He)
n n / / pp ratio ratio : The most important observable used to study the isospin structure of the NMWD.
n / p ratio puzzle
ΓΓpp (Λ+“ p”→ n + p )ΓΓnn (Λ+“ n”→ n + n ) n n / / pp ~~ 0.10.1
Λ N
NNW S
π
One Pion Exchange(OPE)
Simple theoretical model
Tensor-dominant requires the final Nn pair to have isospin 0.
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nn np
pp ppn
n
n p
rescattering
Final state interaction (FSI)
effect
Experimental difficulties in single Experimental difficulties in single nucleon measurementnucleon measurement
Difficulty in detecting neutrons. There is no experiment to observe both of the protons
and neutrons simultaneously with high statistics. Final state interaction (FSI) effect not well established Distinguish between the FSI and ”NNnNN” process
NN→NNN(2N-induced process)
ΛN
NNW π
N
N
(One of the theoretical model)
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np
np
nnp
np
np
npn
Coincidence
Coincidence
NMWD
NMWD
The present experimentThe present experimentKEK-PS E462/E508
1) Angular correlationAngular correlation ( back-to-back, cos<-0.8 ) 2) Energy correlationEnergy correlation ( Q ~ E(N1)+E(N2) ~ 152MeV )
NMWD : N→NN
* cosθ< - 0.8 * E(N1)+E(N2) cut
n
p
p
n
coinpairnpNcoinpairnnN
FSIpn
.avpn
R1
nppN
FSI
2n
.avnn
R1
nnnN
Direct measurement of the n / p ratio
Select N→NN events w/o FSI effect & NN→NNN.
Select light hypernuclei to minimize FSI effect, 5He and 12
C
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π+
K+
Target: 6Li,12C
Excitation-energy spectra for Excitation-energy spectra for 66Li and Li and 1212
CC
6.2×104
events
4.6×104
events
decay counter
6Li (g.s.) 55
He He + p
The ground state of 6Li is
above the threshold of 5He + p.
55HeHe
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Charged particle : ・ TOF (T2→T3) ・ tracking ( PDC )Neutral particle : ・ TOF (target→NT) ・ T3 VETO
p
n
π
K
Decay counter Setup (KEK-PS K6 & SKS)
Decay arm
N: 20cm×100cm×5cm T3: 10cm×100cm×2cm T2: 4cm×16cm×0.6cm
Solid angle: 26%9(T)+9(B)+8(S)%
n
p
polarizationaxis
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The g.s. peak is clearly seen in all spectra with coincident decay particles.
inclusive
w/ proton
w/ pi±
w/neutron
w/ gamma
previous experiment at BNL
Excitation spectra w/ coincident decay particles for Excitation spectra w/ coincident decay particles for 55HeHe
S. Kameoka et al. Nucl. Phys. A754 (2005) 173cS. Okada et al. Nucl. Phys. A754 (2005) 178c
Excitation spectra w/ coincident decay particles for Excitation spectra w/ coincident decay particles for 1212CC
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npnp
n
N→nN
nn np
pp ppn
nn p
NN→nNN FSI re-scattering
nn np
pp ppn
nn p
coun
ts
Q/2Energy spectra (image) Energy
distribute low energy region up to Q/2 broad peak
around Q/2 continuousdistribution
Expected Spectrum9
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Single proton/neutron spectra from Single proton/neutron spectra from 55ΛΛHe and He and 1212
ΛΛCC
S.Okada et al., PLB 597 (2004) 249
Nn ~ 2Np
Calculation byGarbarino et al.
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np- & nn- angular distribution (5ΛHe)
npnn / np = 0.45±0.11±0.03
systematic error is mainly come from efficiency for neutron (6%) + acceptance(3%)
Back-to-back Back-to-back
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Coincidence Measurement (A=12)
cos
n + pn + p
n + nn + n
p + pp + p
EEn +n +EEpp
EEn +n +EEnn
EEp +p +EEpp
MeVMeVNNNN
Cou
nts
Cou
nts
12ΛC
npnn / np = 0.51±0.13±0.05Analysis detail on Kim’s Poster
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10 0.5 1.5n / p
0.93±0.55 (Szymanski et al.) for 5He
Exp
.
Λ N
NNW S
π
One Pion Exchange(OPE)
The
o. N N
NΛ
Direct Quark mechanism
Meson Exchangemechanism
Λ N
NN
π,K,η,ρ,ω…
n n / / pp ratio ratio
Previous exp. (at BNL)
Nnn / Nnp (5He)= 0.45±0.11±0.0355
He (E462)He (E462)Kang et al. PRL 96 (2006) 062301 Γn / Γp (12
C)= 0.51±0.13±0.051212C (E508)C (E508)
Kim et al. PLB641 (2006) 28
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Asymmetry measurement of decay proton
N() = N0(1 + Acos)
Asymmetry
Asymmetry : Volume of the asymmetric emission from NMWD
A = (R - 1)(R + 1)
R =N(-) N(+)
,
Asymmetryparameter
= N0(1 + Pcos)
Difference of acceptance & efficiency → canceled out !!
R =N(+(-))×N(-(+)) N(+(+))×N(-(-))
1/2
K >0
+ K+
/p
K
K <0
+K+
/pK
P
P
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Initial state Final state Amplitude Isospin Parity
1S0
1S0 a 1 No3P0 b 1 Yes
3S1
3S1 c 0 No3D1 d 0 No1P1 e 0 Yes3P1 f 1 Yes
If assuming initial S state
)}(3{41])2(3)2([23
222222 fedcbafdcdcbaeNM
p
We can know the interference between states withdifferent Isospin and Parity .
222222
222 )(2/fedcba
fbapn
(Applying =1/2 rule)
Importance of αnm measurement 15
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NM for 5ΛHe NMWD
A=PA:Asymmetry of PionAsymmetry Parameter of Pion (= - 0.642±0.013)PPolarization of Lambda:Attenuation factor
・Polarization of
・ Asymmetry Parameter of ProtonAp=NMPp
Estimated from mesonic decay
We can calculate NM without theoretical help !p
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Theory: - 0.6 ~ - 0.7
Asymmetry parameter of 5ΛHe
NM=0.08±0.08+0.08 psta
tistic
al
contam
i
-0.00
Nucl.Phys.A754 (2005) 168cnucl-ex/050916
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Asymmetry parameter of 12C, 11B
NM= - 0.14±0.28+0.18 psta
tistic
al
contam
i
-0.00
E160 : - 0.9±0.3
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Comparison with previous experimentP
ID fu
nctio
nE
nerg
y sp
ectru
m
p
Precious Experiment E508
w/protonw/proton w/pion
range&EtotdE/dx&Etot
TOF&Etot
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)}(3{41])2(3)2([23
222222 fedcbafdcdcbaeNM
p
Comparison with recent calculations
OPE
+K
+K+DQ
OME
+K,OME can reproducen/p ratio but predict large negative NM
+K+
+K++DQ
n/p and NM can bereproduced by+K++DQ model
Sasaki et al.PRC71 (2005)035502
(1) Large b(1S0→3P0) and f(3S0→3P1) amplitude(2) Violation of ΔI=1/2 rule considered
T. Maruta ; parallel A2a Calculation by Itonaga
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Decay Widths → Okada’s poster21
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SummarySummary N→NN was directly observed for the first time !! 5
ΛHe : Γn / Γp ratio ~ Nnn / Nnp = 0.45±0.11±0.03 Kang et al. PRL 96 (2006) 062301 12
ΛC : Γn / Γp ratio = 0.50±0.13±0.05 Kim et al. PLB641 (2006) 28
◆ Asymmetry parameter measured with improved accuracy !! 5
ΛHe :
11ΛB and 12
ΛC : Maruta et al. nucl-ex/0509016; thesis
◆ Total & partial decay rates are measured very accurately
NM=0.08±0.08+0.08p
[1] Importance of shorter-range mechanism OPE ⇒ Heavy meson & DQ exchange [2] Suggesting significant contribution from ΛN initial spin-singlet initial state σ-meson exch. / ΔI=1/2 violation? ⇒ 4
ΛH & ΛΛ→ΛN@J-PARC
-0.00
NM= - 0.14±0.28+0.18p -0.00
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Spare OHPs
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Neutron energy resoltion→7MeV(FWHM) at 75MeV
Neutral PIDNeutral PID
Constant background very small
1 / spectra
Neutral particles from 12C
Good n separation
Charged particles from 5He
PID function
Charged PIDCharged PID
Good p d separation
Decay particle identificationDecay particle identification8
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expe
rimen
tal
expe
rimen
tal
data
data
theo
retic
al
theo
retic
al
calc
.ca
lc.
Comparison with theoretical calc.for angular correlation
Garbarino’s calc.
assuming Gn/Gp = 0.46 (for 5He ), 0.34 (for 12
C )considered 2N-induced( ~ 20%), FSI
55He (E462)He (E462) 1212
C (E508)C (E508)n+p coincidencen+n coincidence
n+pn+n
cos cos
n+p coincidencen+n coincidence
n+pn+np+pp+p
Pair numberPair number /NMWD/NMWD
Pair numberPair number /NMWD/NMWD
n+p coincidencen+n coincidencep+p coincidencen+p coincidencen+n coincidencep+p coincidence
Phys. Rev. Lett. 91 (2003) 112501Phys. Rev. Lett. 91 (2003) 112501 21
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Neutron Efficiency Correction
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NNn n / N/ Npp Ratio Ratio
ΓΓnn (Λ+“ n”→ n + n )
ΓΓpp (Λ+“ p”→ n + p )
If Γn / Γp = 1 → Nn / Np = 3
If Γn / Γp = 0.5 → Nn / Np = 2
If Γn / Γp = 0 → Nn / Np = 1
Naive estimationNaive estimation(without considering FSI and ΛNN→NNN)
To avoid suffering from FSI effect & ΛNN→NNN,High energy threshold High energy threshold
Γn:Γp Nn Np
1 : 1 … 3 : 1 1 : 2 … 2 : 1 0 : 1 … 1 : 1
Nn / Np = 2×n / p + 1
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Mass number dependence Mass number dependence of neutron energy spectra ( A=5,12,89 )of neutron energy spectra ( A=5,12,89 )
( previous experiment )
As the mass number become lager, the number of neutron become lager in the low energy part, and smaller in the high energy part.
Q / 2 = 76 MeV
No peaking at Q / 2 (76MeV)
even 5ΛHe
suggested larger contribution of ΛNN→NNN or FSI than theoretical prediction.
Theoretical calc.
5ΛHe
w/ FSI
Q/2
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Spare OHPsfor asymmetry
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E160 E508Statistical comparison with E160
12C event 246 event
11B event 393 event
2779 event
2122 event
×11
×5
Total 639 event 4901 event×8
P-coinspectrum
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Comparison with E160PID function Energy spectrum
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• Polarization (P), asymmetry parameter(a)
1
14uA
uB
dA
dB
dB
dA
uB
uA
A1A1
)(N)(N)(N)(N)(N)(N)(N)(N
4.03.1a p1
Asymmetryparameter
S.Ajimura et al., PLB282, 293 (1992)
W() = 1 + A1P1(cos) A1 = ka1P
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• KEK-PS E278 experiment
Experimental target: 6LiObservable: Mesonic decay branching ratios Polarization
E278 Decay counter
/ p separation by dE/dx and Etot
pHeLi 56
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Polarization of 5He
6Li(+, K+) spectrum
PA
A1A1
)(N)(N)(N)(N
S. Ajimura et al., PRL80, 3471 (1998)
Consistent with experimental data
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Proton asymmetry parameter of 5He
pp
p
p
pp
pp
PA
A1A1
)(N)(N)(N)(N
6Li(+, K+) spectrum
S. Ajimura et al., Submitted to PRL
Inconsistent with meson exchange model
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Polarization of
ー : E462
ー : E278
: Motoba et al. NPA577 (1994) 293c
NOTE:Calculation by Motoba et al. considers excited state at E=4.5 MeV
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E462
- / of He
- branching ratio0 branching ratio
Lifetime
Other resultsOther results
- decay width for 5He
Errors were much improved !!
0 decay width for 5He and 12
C
HYP2003 proceedingsNucl. Phys. A754 (2005)
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Null asymmetry test(,pX) reaction : Only Strong Interaction
Asymmetry = 0 expectedAsymmetry of
6Li target- 0.000± 0.0020.003± 0.0020.003± 0.002- 0.001± 0.0010.003± 0.0010.000± 0.001
6<|θ |<9°9<|θ |<15°
6<|θ |<9°9<|θ |<15°2<|θ |<6°
Scattering Angle2<|θ |<6°
Horizontal
Proton
Pion
Instrumental Asymmetry < 0.3%
p or
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np coincidence analysis
Asymmetryθ <0 θ >0 Parameter
23/ 26 30/ 19 0.176±0.122 0.306±0.215Asymmetry
6<|θ |<15°
Horizontal Scattering Angle
Nupper/ Nlower
np
np
nnp
np
Coincidence
NMWD
np back-to-back event
NM=0.31±0.22p
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One and only(?) solution
+ K + + DQSasaki et al.PRC71 (2005)035502 N
NNW S
,K,
b(1S0→3P0) と f(3S0→3P1) amplitude に影響を与えるI = 3/2 が大きく寄与する
今回 n/p ratio と NM を高精度で測定したことにより、 こういう反応機構の必要性が認識された。
p
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Mijung のOHPから
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0034.00113.0
)018.0060.0()326(
a
0038.00156.0
)0204.00833.0()326(
b
Before subtraction After subtraction
)7.0(cos npnpN
)7.0(cos nnnnN
0138.01384.0
0144.00826.0 0149.00670.0
0142.01272.0
Uniform components subtractionUniform components subtraction
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FSI consideration using pp-pairs rrn,pn,p fraction ratio of the neutron and proton induced channels.ffn,pn,p is reduction factor due to FSI.ggn,n,pp is cross over influx of neutron(proton) from proton(neutron) due to FSI.p,q,q’p,q,q’ are angular acceptance factor.
fff np ggg np 02 gpn rrx /
0)(2 ''''2 ppnnnppp NNxNNx
,,,, ,,
Nnp(bb) 0.1272 0.0142
Nnn(bb) 0.0670 0.0149
Npp(bb) 0.0047 0.0017
MeVEthNN 30,7.0cos At
'2'
'
2'
2
qgrqgfrN
qgfrpffrN
qgfrpfrN
pnppppp
pnnpnpnp
nnpnnnn
))(( 'NNNN NbbN
Before FSI correctionBefore FSI correction
13.053.0)()(
bbNbbN
np
nn4%4%
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Systematic error calculationSystematic error calculation
05.013.051.0
p
n
1)1) Intentionally add 2Intentionally add 2 pp pp events events inin
-0.8<cos-0.8<cos<-0.7 <-0.7 %4:13.049.0
2)2)
3)3)Uniform b.g. level for different angular regions:6.6%Uniform b.g. level for different angular regions:6.6%
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6Li Hypernuclear mass spectra6Li + +→ 6Li + K+
6Li → 5He + p
5He
6Li
5Li0MeV
8.3MeV
18.3MeV
(Pn-1,S)
(Pn-1,P)
(Sn-1,S)
p decay
decay
inclusive
coin
p coin
5.2×104 events
3.2×103 events
1.6×103 events
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Instrumental Asymmetry
(,pC) reaction : Only Strong InteractionAsymmetry = 0 expected
6Li target 12C target- 0.000±0.002 0.000± 0.0020.003± 0.002 -0.003±0.0030.003± 0.002 0.001± 0.002- 0.001±0.001 -0.002±0.0020.003± 0.001 0.002± 0.0020.000± 0.001 -0.003±0.002
Proton
Pion
6<|θ |<9°9<|θ |<15°2<|θ |<6°
Scattering Angle2<|θ |<6°
Horizontal Asymmetry
6<|θ |<9°9<|θ |<15°
Instrumental Asymmetry < 0.3%
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Spin / isospin dependence
p p n Λ
He4Λ
n n p Λ
H4Λ
p p n n Λ
He5Λ
Non-mesonic weak decay of 4He and 4
H
4He (K-,-) 4He or
4He (+,K+) 4He
n+n back-to-back4He (K-,0) 4
H p+n back-to-back (0 spectrometer )
see S.Ajimura : J-PARC LOI 21
To J-PARCTo J-PARC
RNS … N : nnn, pnp S : spin = 0 or 1
nm(4H) = ( 3Rn1+ Rn0 + 2Rp0 ) ×4 / 6
nm(4He) = ( 2Rn0 + 3Rp1 + Rp0 ) ×4 / 6
nm(5He) = ( 3Rn1+ Rn0 + 3Rp1 + Rp0 ) ×5 / 8
Need one-order higher statistics. J-PARC
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π+
K+decay
counter
K6/SKS setup
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Identification of hypernuclear formation
21
pM scattered
K+
T1 target
Z-vertexMass
Z
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Non-mesonic weak decayNon-mesonic weak decay
strong tenser coupling (L=2, S=2)→ dominant term 3S1→3D1 (amplitude “d”)
+ N→ N + N + p → n + p: p = a2+b2+c2+d2+e2+f2
+ n → n + n : n = a2+b2+f2
OPE : n / p ~ 0.1
Λ N
NNW S
π
One Pion Exchange (OPE) model
n / p ratio: The most important observable to study the isospin structure of the NMWD.
Exp. : n / p ~ 1n / p ratio puzzle
Simple theoretical model
with large error
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-nucleus overlap for 5He
0 / = 0.201±0.011 (He)
nm/ = 0.395±0.016 (He)
Γtotal (Γtotal (5656ΛΛFe) Fe) ~~ Γnm(A→∞) Γnm(A→∞) ~ ~ 1.2Γ1.2ΓΛΛ ( ( E307E307 ))
Γnm (Γnm (55ΛΛHe) = 0.4ΓHe) = 0.4ΓΛΛ ( ( Present)Present)
1/3 of Λ is inside α 1/3 of Λ is inside α
Both results are consistent,Both results are consistent,preferred larger overlap than YNG prediction.preferred larger overlap than YNG prediction.
55ΛΛHe (ORG) He (ORG) ~ ~ 40%40%
55ΛΛHe (YNG) He (YNG) ~ ~ 20%20%
1/3 of Λ is inside α 1/3 of Λ is inside α
0 / locates in between ORG and YNG.
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ちょっと前の講演のから ..
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Mesonic Weak Decay Decay mechanism is known fairly well “How to use it”
Mass number
4 ~ 5
~ 10
50 ~ 100
q ~ 400MeV/cΛN→NN
•Spin/isospin dep.•ΔI=1/2 rule test
)( Anm
Mass number dependence
Λ→Nπ•Λ-nucleus potential•Spin/parity assignment Pion distortion effect in nuclei
q ~ 100MeV/c
Non-Mesonic Weak Decay (NMWD) Decay mechanism is unknown “What is it ?”
Fermi momentum~ 270MeV/c >>
4
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History of hypernuclear History of hypernuclear weak decay experiments… weak decay experiments…
Year
~ 1960
1985
1995
2000 ~ 2002
2004 ~
ΓΓππ__ (→ p + π - )
ΓΓππ00 ( → n + π 0 )
ΓΓpp ( +“ p”→ n + p )ΓΓnn ( +“ n”→ n + n )
1/HY =Γtot
Γm
ΓnmNew era started!→ FINUDA@DAFNE / J-PARC
Merit/Demerit
* Clean decay identification→ ground state spin assignment* Low energy threshold for p* Hypernuclear formation is not identified* Blind for neutral particles* No timing information
* Hypernuclear formation tagged → branching ratio !* Direct lifetime meas. w/TOF counter
* Still hard to see neutral particles* High energy threshold for p (Ep>30 ~ 40MeV)
Emulsion andBubble chamber
Method
Counter experimentstart @BNL/KEK w/ (K,π)
SKS experimentsw/ (π,K) reaction
n+p/n+ncoincidence
* Heavy Λ hypernuclear production* Neutral particle detection* Asymmetry of p from NMWD * Improved statistics → n+p/n+n double coincidence
7
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Hyperon-nucleus potential Hyperon-nucleus potential
ΛnucleusYN interaction attraction ~ repulsion
Repusive core is the common feature of Y-nucleus potential
18
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Spin/isospin dependence
8/RR3 R R3 = He
6/RR3 R2 = He6/R2 R R3 = H
50p1p0nn15
nm
40p1pn04
nm
40p0nn14
nm
Test of =1/2 ruleI0/1=Spin S
nnn npp N RNS
??)He(2)H(rule 1/2I ? 2
44p0n0
np
RR
p p n Λ
He4Λ
n n p Λ
H4Λ
p p n n Λ
He5Λ
NMWD ofNMWD of 4 4ΛΛHe and He and 44
ΛΛHH
×
35
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Theoretical approachTheoretical approach
N N
NΛ
Direct Quark (DQ) mechanism
q ~ 400MeV/c (← large!) → short-distance interaction
One Meson Exchange (OME) mechanism
Λ N
NN
π,K,η,ρ,ω,K*
→ large n / p ( ~ 0.4-0.7)
• Kaon exchange model (OME)
dominant term 3S1→1P1 (amplitude “f”)
( range ~ 0.5 fm)
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Hypernuclear mass spectra on C, Si and Fe target
natC(+,K+) natSi(+,K+) natFe(+,K+)
45
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KEK-E307
COSY-13dr
ρΓ 2
Λ0
2N
nm
?
Lifetime of very-heavy hypernuclei ? (J-PARC)
(π,K) K1.1BR
49
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By-products of E307 exp.By-products of E307 exp.
1. Mesonic decay widths of midium-heavy Λ hypernuclei
2. Proron energy spectra → Γn/Γp ratio “puzzle”
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Enhancement of π-mesonic Enhancement of π-mesonic decay widthsdecay widths
Momentum transfer q ~ 100MeV/c << 270MeV/c→ “ Forbidden” process in nuclear matter
1. Fermi motion of Λ2. Smaller local Fermi momentum at the surface regi
on3. Pion distortion effect 1) Pion feels attraction in nuclear medium due to the P-wave part of the optical potential 2) Inside the nucleus, pion can carry smaller energy for fixed momentum q
3) Due to the energy conservation, final nucleon has more chance to come out above the Fermi surface
22)( mqq
<
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Effects of nuclear shell structure and -nucleus potential
T. Motoba et al. Prog. Theo. Phys. Suppl. No.117, 477 (1994)
H. Noumi et al. PRC52, 2936 (1995)J. J. Szymanski et al. PRC43, 849 (1991)A.Sakaguchi et al. PRC43, 73 (1991)T. Motoba et al., PTP Suppl. No.117, 477 (1994)
Potential dependence of decay rate mesonic decay rates for p-shell hypernuclei
52
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Hypernuclear mass spectra on C, Si and Fe target
natC(+,K+) natSi(+,K+) natFe(+,K+)
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Results of - Mesonic decay width
CL) (90%012.0)(
015.0008.0032.0)(
002.0008.0036.0)(
036.0027.0170.0)(
004.0011.0099.0)(
27
28
11
12
FeB
AlB
SiB
BB
CB
Branching ratio
CL) (90%015.0)(
019.0010.0041.0)(
002.0011.0046.0)(
045.0036.0212.0)(
005.0014.0113.0)(
27
28
11
12
Fe
Al
Si
B
C
- Mesonic decay width
Motoba
Motoba
Y.Sato et al.Recently re-submitted to PRC
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Gross behavior of hypernuclear -mesonic decay rate
E.Oset et al. Prog. Theo. Phys. Suppl. No.117,461 (1994) T. Motoba et al. Nucl. Phys. A547, 115c (1992)
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Measurement of π0 Measurement of π0 mesonic decay mesonic decay
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one gamma ray from “0 2” process was detected.
For observing 0 particle,
Constant backgroundlevel is very low.
Gated ground state of hypernuclei (5He, 12
C)
1 / 1 / ( TOF ) spectrum ( TOF ) spectrum
Neutral particle identificationNeutral particle identification
Layer multiplicity 2
ADC sum 20MeVee
Good separation (between and neutron) 34
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Large plastic scintillator arrays were used as detector.
Start timing counter
Charged VETO30
cm
detection system
00 identification identification
Background (low energy): from nuclear decay process
0
EM shower
(~70MeV)
K++
0 emit energetic gamma. (~70MeV) set threshold of ADC sum. The gammacascade in many layers. select high multiplicity event.
To reject the nuclear decay
In these cut conditions, It is hard toestimate gamma detection efficiency. So we simulated with same conditions using GEANT code.
5He
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Mul 2
Mul 3
Mul 4
Mul 5
Mul 6
Layer multiplicity
ADC sum distribution ADC sum distribution
Mul 1
efficiency estimation using GEANT simulationefficiency estimation using GEANT simulation
* Blue histogram : GEANT simulation * Plot (with error bar) : Experimental data
Nuclear is shown only Mul 1.To remove it completely,we apply Mul 2 andADCsum 20MeVee .
Well agree with Geant simulation.
assuming 0 momentum in GEANT simulation as 5He : 104.9 MeV (mono)
12C : Motoba’s calculation
PTP117(1994)
from 0
20MeV
nuclear
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00 branching ratio of branching ratio of 55HeHe
Free b / b0 = 1.78±0.03
5Heb / b0 = 1.70±0.08
MeV
Mass spectra for Mass spectra for 66Li(Li(++,K,K++) ) 5He g.s.
quasi free
w/ gamma
Mul 220 MeVee
inclusiveefficiency= 9.59%N (inc)
= 42040
N (w/ )= 848.03
b0 = N (w/ ) / N (inc) × eff = 0.212±0.008
ADC sum w/ Geant simADC sum w/ Geant sim
5He
+ p + + n + 0
Same Q-value as that of free
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Results of Results of 00
He0 / = 0.201±0.011
C0 / = 0.165±0.008Lifetime : 278+11 ps (E462)
-10 Lifetime : 212+7 ps (E508)
-6
Much improved accuracyOkada et al., HYP03 nucl-ex/0402022
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Fuse-Kumagai’s recent calculationJPS meeting (2004 Spring)
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SG: excluded→ Existence of repulsive core!!
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Henm/ = 0.406±0.020
Cnm / = 0.953±0.032
tot = 0.947±0.038 ΓΛ
bπbπ00 = = 0.212±0.008 bπbπ-- = = 0.359±0.009 bπbπ-- = = 0.099±0.011
bπbπ00 = = 0.133±0.005
tot = 1.242±0.042 ΓΛ
0.41±0.140.41±0.14 0.83±0.090.83±0.09
Non-mesonic deca rate Non-mesonic deca rate 55He and He and 1212
ΛΛCC
Γtotal (Γtotal (5656ΛΛFe) Fe) ~~ Γnm(A→∞) Γnm(A→∞) ~ ~ 1.2Γ1.2ΓΛΛ ( ( E307E307 ))
Γnm (Γnm (55ΛΛHe) = 0.4ΓHe) = 0.4ΓΛΛ ( ( Present)Present)
Γnm calculation must use the Λ w.f.Γnm calculation must use the Λ w.f.which can well reproduce Γπwhich can well reproduce Γπ
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Mass number dependence of ΓMass number dependence of ΓNMNM
42