Decay asymmetry in non-mesonic weak decay of light L hypernuclei
description
Transcript of Decay asymmetry in non-mesonic weak decay of light L hypernuclei
Decay asymmetry in non-mesonic weak decay of light hypernuclei
T.MarutaKEK,
JSPS fellow
Oct./13/2006 HYP2006@Mainz Univ.
KEK-PS E462/E508 collaborations
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Asymmetry measurement of decay proton
Asymmetry : Volume of the asymmetric emission from NMWD
Difference of acceptance & efficiency is canceled out !
K >0
+ K+
/p
K
θ
P
K <0
+K+
/p
K
θ
P
N(θ) = N0(1 + Acosθ)
Asymmetry
A = (R - 1)(R + 1)
R =N(θ-) N(θ+)
,
Asymmetryparameter
= N0(1 + Pcosθ)
R =N(θ+(-))×N(θ-(+)) N(θ+(+))×N(θ-(-)) 1/2
polarization in n(+,K+)
K+ scattering angle(K)
1.05GeV/c +
E278
In large scattering angle, is much polarized.
accepted
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If assuming initial S state
We can know the Interference between differentIsospin and Parity states.
Importance of NM measurement
StateParity Isospin
Amplitude
Initial Final Ifz = 0 If
z = -1
1S0
1S0 PC 13P0 PV 1
3S1
3S1 PC 0 ー3D1 PC 0 ー1P1 PV 0 ー3P1 PV 1
: d K : f
p
p
p
p
p
p
p
a
b
c
d
e
f
n
n
n
a
b
f
2 2 2 2 2 2
2( 3[ ] [ ] 2[ ] 6[ ] 3[ ])
| | | | 3(| | | | | | | | )p p p p p p p p p pNM
pp p p p p p
a e b c b d c f d f
a b c d e f
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Motivation
Theoreticalprediction
-0.6 ~ -0.7
Previousexperiments
5He : 0.24±0.22
The aim of E462/E508 experiment
Ajimura et al.
Precise measurement of Asymmetry parameter high statistics
Reduction of Statistical error. p-n coincidence measurement
p→np measurements of 5He and 12C,11B in same setup
possible to compare them in low systematic error
Present status
12C,11B : -0.9±0.3
OME Ex.+K+DQ Ex. etc.
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Excitation spectra w/ coincident decay particles for 6Li
inclusive
w/ proton
w/ pion
4.0×104
contamination in p-gate Systematic error
PID spectrum6Li → 5He+p
++6Li → K++6Li
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Null asymmetry test(, pX) reaction : Only Strong Interaction
Asymmetry = 0 expectedAsymmetry of
6Li target- 0.000± 0.002
0.003± 0.002
0.003± 0.002
- 0.001± 0.001
0.003± 0.001
0.000± 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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Procedure for NM calculation (5He)
A= P
A: Asymmetry of : Asymmetry Parameter of mesonic decay (=-0.642±0.013)PPolarization of : Attenuation factor (Monte-Carlo simulation)
・ Polarization of
・ Asymmetry Parameter of Proton
Ap = NMPp
p
Estimated from mesonic decay
We can obtain NM without theoretical help.p
M
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Theory: - 0.6 ~ - 0.7
Asymmetry parameter of 5He
NM=0.08±0.08+0.08 pst
atis
tical
conta
mi
-0.00
5He
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np coincidence analysis
Asymmetry Asymmetry
θ K<0 θ K>0 (Ap) Parameter
19/ 22 26/ 18 0.15±0.13 0.31± 0.286<|θ K|<15°
Horizontal
Scattering AngleNU/ ND
np
np
nnp
n
p
Coincidence
NMWD
np opening angle
cosθ
cosθ<-0.85He
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Excitation spectra w/ coincident decay particles for 12C
B + p11
C + 11
C 12
p decay
B 11
0.0MeV
6.3MeV
2.5MeV
8.1MeV
decay
depolarizedeffect
inclusive
w/ proton
w/ pion
5.8×104 Level scheme of 12C
LH
N,decay
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Polarization of (12C,11B)Itonaga et al.Prog. of Theo. Phys. Supp. 117(1994)14
2o 6~ o 6o 9~ o 9o 15~ o
12C 0.052 0.084 0.12211B 0.048 0.081 0.122
P Kaon Scattering angle
M1 transitionreduces
Polarization of
2o 15o
If assuming polarization isproportional to scattering angle.
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Asymmetry parameter of 12C, 11B
NM=-0.14±0.28+0.18 pst
atis
tical
conta
mi
-0.00
E160 : - 0.9±0.3
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Comparison with recent results
+2/+2/++K+/a1
Itonaga et al.OPE
+K+DQ
+K
OME
p
Theoretical models such as +K reproduce n/p ratio, but predict large negative NM.
+K+
+K++DQ
+K++DQ model reproduces both n/p ratio and NM.
p-shell
Sasaki et al.PRC71 (2005) 035502
(1) Large b(1S0→3P0) and f(3S0→3P1) amplitude(2) Violation of I=1/2 rule considered
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Summary
A series of experiments, E462 (5He) and E508 (12C, 11B) were carried out to measure NM precisely.
We obtained nearly zero NM’s (0.08±0.08+0.08, -0.14±0.28+0.18) in both nuclei. We don’t observe the difference in both reaction mechanism.
Recent theoretical calculation indicates the contribution of the initial state of 1S0. For more check, measurement of 4H is required at J-PARC.
-0.00 -0.00
p
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Spare OHP’s
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Excitation spectra w/ coincident decay particles for 6Li
inclusive
w/ proton
w/ pion
6Li (6Li→5He+p)
4.0×104
contamination in p-gateSystematic error
PID spectrumprevious experiment at BNL
6Li(K-,-)6Li
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Proton Energy Dependence (5He)
Proton
Th
res
ho
ld
(Co
un
ts/5
MeV
)
0.07±0.09+0.09
0.15±0.10+0.09
0.05±0.14+0.08
Q/2Low energy region
Contamination of FSI 2N-induced
5He の結果における FSI 等の効果は小さいと考えられる -0.00
-0.00
-0.00
Neutron
Ep 30MeV -0.46 50MeV -0.52 70MeV -0.55
Garbarino’s calculation(with FSI effect)
PRL94 (2005) 082501
th
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Production of polarized hypernuclei
E462/E508 experiments 1.05GeV/c + beamis injected.
Distribution of polarization in the n(+,K+) reaction.
K+ scattering angle(K)
1.05GeV/c +
In large scattering angle, is much polarized.
P
+
K+
/p
K
θ
E278
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Polarization of
ー : E462
ー : E278
: Motoba et al. NPA577 (1994) 293c
Motoba et al.g.s.+4.5MeVex. state
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One solution
+ K + + DQ
Sasaki et al.PRC71 (2005)035502 N
NN
W 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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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([23222222 fedcba
fdcdcbaeNMp
We can know the Interference between states withdifferent Isospin and Parity .
222222
222 )(2/
fedcba
fbapn
(Applying I=1/2 rule)
Importance of asymmetry measurement
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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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Charged particle identification
TOF
dE/dx
E VS. TOF
E VS. dE/dx
T2
ener
gy
loss
(M
eVee
)T
OF
(1
/)
d
e
Total E (MeVee)
PID1
PID2
PID1
PID2
Total E
p
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Comparison with E160P
ID f
unct
ion
Ene
rgy
spec
trum
p
E160 E508
w/protonw/proton w/pion
range&EtotdE/dx&Etot
TOF&Etot
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Proton asymmetry of 12C and 11B
KEK E369 dataExcitation spectrum w/proton
Excitation spectrum of 12C is well known from previous experiment
eliminate the contamination such as QF event inside the gate
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Asymmetry of 5He spectra
w/ proton w/ pion
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Asymmetry parameter of mesonic decay
0 1 10 1 0
1 0 12 1
0 1 03 3S Y P Y Y
2 2
2Re *
| | | |
S P
S P
→ - + ps 1/2 0 1/2
l =0,1
wave function:
Angular distribution of decay proton1 -sinθ cosθ
2 2* | | | | 2Re * cosS P S P θ Asymmetry parameter
S : 88%、 P : 12% = 0.64
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One (Sasaki et al.) solution
Ex.+ K Ex. + Ex+D.Q.
n/
p r
atio
N
M p
weak coupling constant of meson
Sasaki et al.PRC71 (2005)035502
Both n/p and NM are consistent with experimental value.
N
NN
W S
,K,
p
Exp
eri
me
nta
lva
lue
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PID1 ( dE/dX .vs. Etotal )
PID
2 (
TO
F .
vs.
Eto
tal )
PID window
(+, pX) reaction
or p
p gate gate
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Identification of hypernuclear formation
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p
M scattered
K+
+
T1 target
K
~ 340psec
0 1-1 2-2 3-3 (ns)0
2000400060008000
200 400 600 800 1000 12000(MeV/c2)
-200-400-600-800 0 200(mm)
Good /K separation Good /K/p separation
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Neutron spectrum for 5He
Theoretical calc.
No peaking at half of Q-value (76MeV) even 5
ΛHesuggested larger contribution of NN→NNN or FSI than theoretical prediction.
Q / 2 = 76MeV
Theory :Garbarino et al.PRC69 (2004)054603
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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
MeVMeVθθNNNN
Co
un
tsC
ou
nts
12ΛC
npnn / np = 0.51±0.13±0.05Analysis detail on Kim’s Poster
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