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Oct./13/2006 [email protected] Univ. Decay asymmetry in non-mesonic weak decay of light L hypernuclei. T.Maruta KEK, JSPS fellow. KEK-PS E462/E508 collaborations. L polarization in n( p + , K + ) L. 1.05GeV/ c p +. accepted. P. L. p /p. E278. θ. K +. p +. K + scattering angle( j K ).

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decay asymmetry in non mesonic weak decay of light l hypernuclei

Oct./13/2006 [email protected] Univ.

Decay asymmetry in non-mesonic weak decay of lightLhypernuclei

T.Maruta

KEK,

JSPS fellow

KEK-PS E462/E508 collaborations

asymmetry measurement of decay proton

Lpolarizationinn(p+,K+)L

1.05GeV/cp+

accepted

P

L

p/p

E278

θ

K+

p+

K+ scattering angle(jK)

jK

1/2

N(q+(+j))×N(q-(-j))

R =

Inlarge scattering angle,

Lis much polarized.

N(q+(-j))×N(q-(+j))

jK <0

jK

p+

K+

θ

p/p

P

L

Asymmetry measurement of decay proton

Asymmetry : Volume of the asymmetric emission from NMWD

N(q) = N0(1 +Acosq)

jK >0

Asymmetry

=N0(1 +aPcosq)

L

Asymmetry

parameter

(R + 1)

N(q+)

A =

R =

,

(R - 1)

N(q-)

Difference of acceptance & efficiency is canceled out !

importance of a nm measurement
Importance ofaNM measurement

p

If assuming initial S state

p : d

K : f

We can know the Interference between different

Isospin and Parity states.

motivation
Motivation

Present status

Previous

experiments

Theoretical

prediction

5He : 0.24±0.22

L

-0.6~-0.7

12C,11B : -0.9±0.3

OME Ex.

p+K+DQ Ex. etc.

L

L

Ajimura et al.

The aim of E462/E508 experiment

Precise measurement of Asymmetry parameter

  • high statistics
    • Reduction of Statistical error.
  • p-n coincidence measurement
    • Lp→np
  • measurements of 5He and 12C,11B in same setup
    • possible to compare them in low systematic error

L

L

L

slide5

L

6Li → 5He+p

L

Excitation spectra w/ coincident decay particles for 6Li

L

p++6Li → K++6Li

L

PID spectrum

inclusive

4.0×104

w/ proton

w/ pion

pcontamination in p-gate

Systematic error

null asymmetry test
Null asymmetry test

(p, pX)reaction : Only Strong Interaction

p or p

Asymmetry = 0expected

Instrumental Asymmetry<0.3%

procedure for a nm calculation 5 he

Ap = ap hPL

Ap: Asymmetry ofp

ap: Asymmetry Parameter of mesonic decay

(=-0.642±0.013)

PL: Polarization of L

h: Attenuation factor (Monte-Carlo simulation)

We can obtainaNMwithout theoretical help.

p

Procedure for aNM calculation (5He)

p

L

Estimated from mesonic decay

・Polarization ofL

M

・Asymmetry Parameter of Proton

p

Ap = aNMhPL

asymmetry parameter of 5 he
Asymmetry parameter of 5He

Theory: - 0.6~- 0.7

5He

L

L

statistical

p contami

aNM=0.08±0.08+0.08

-0.00

p

np coincidence analysis

L

Coincidence

p

p

p

p

n

n

n

n

n

np coincidence analysis

np opening angle

5He

cosq<-0.8

NMWD

cosq

excitation spectra w coincident decay particles for 12 c

11

LB +p

Excitation spectra w/ coincident decay particles for 12C

L

Level scheme of 12C

L

5.8×104

inclusive

N,a decay

LH

p decay

11

C +L

w/ proton

LB

8.1MeV

11

6.3MeV

w/ pion

gdecay

2.5MeV

depolarized

effect

0.0MeV

LC

12

polarization of l 12 c 11 b

2o

15o

Polarization of L (12C,11B)

L

L

Itonaga et al.

Prog. of Theo. Phys. Supp. 117(1994)14

If assuming polarization is

proportional to scattering angle.

M1 transition

reduces

Polarization ofL

asymmetry parameter of 12 c 11 b

statistical

p contami

aNM=-0.14±0.28+0.18

p

E160 : - 0.9±0.3

Asymmetry parameter of 12C, 11B

L

L

-0.00

comparison with recent results

Theoretical models such as p+K reproduce Gn/Gp ratio, but predict large negative aNM.

p+K+DQ

p

  • p+K+s+DQ model reproduces both Gn/Gp ratio and aNM.

p+K+s

OME

p+K+s+DQ

Sasaki et al.

PRC71 (2005) 035502

p+K

(1) Large b(1S0→3P0) and

f(3S0→3P1) amplitude

(2) Violation of DI=1/2

rule considered

p+2p/r+2p/s+w+K+rp/a1

Itonaga et al.

OPE

Comparison with recent results

p-shell

summary
Summary
  • A series of experiments, E462 (5He) and E508 (12C, 11B) were carried out to measure aNM precisely.
  • We obtained nearly zero aNM’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.

L

L

L

p

-0.00

-0.00

L

slide16

previous experiment at BNL

6Li(K-,p-)6Li

L

Excitation spectra w/ coincident decay particles for 6Li

L

6Li (6Li→5He+p)

PID spectrum

L

L

L

inclusive

4.0×104

w/ proton

w/ pion

pcontamination in p-gate

Systematic error

proton energy dependence 5 he

Garbarino’s calculation

(with FSI effect)

Ep 30MeV -0.46

50MeV -0.52

70MeV -0.55

0.05±0.14+0.08

0.15±0.10+0.09

0.07±0.09+0.09

Proton Energy Dependence (5He)

L

Q/2

  • Low energy region
  • Contamination of
    • FSI
    • 2N-induced

Neutron

Proton

Threshold

(Counts/5MeV)

th

-0.00

PRL94 (2005) 082501

-0.00

-0.00

5Heの結果におけるFSI等の効果は小さいと考えられる

production of polarized hypernuclei
Production of polarized hypernuclei

1.05GeV/cp+beam

is injected.

E462/E508 experiments

Distribution ofLpolarization

in then(p+,K+)Lreaction.

1.05GeV/c p+

P

L

p/p

θ

K+

jK

p+

E278

K+ scattering angle(jK)

Inlarge scattering angle,Lis much polarized.

polarization of l

ー : E462

ー: E278

: Motoba et al.

NPA577 (1994) 293c

Polarization of L

Motoba et al.

g.s.+4.5MeVex. state

one solution

N

N

S

W

N

p,K,s

L

One solution
  • + K + s + DQ

Sasaki et al.

PRC71 (2005)035502

  • b(1S0→3P0)とf(3S0→3P1) amplitudeに影響を与える
  • DI = 3/2が大きく寄与する
  • 今回Gn/Gp ratioとaNM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

importance of asymmetry measurement
Importance of asymmetry measurement

If assuming initial S state

(ApplyingDI=1/2 rule)

We can know the Interference between states with

different Isospin and Parity .

decay counter setup
Decay counter Setup

π

p

n

n

K

p

(KEK-PS K6 & SKS)

Decay arm

Solid angle: 26%

9(T)+9(B)+8(S)%

polarization

axis

Charged particle:

・TOF (T2→T3)

・tracking(PDC)

Neutral particle:

・TOF (target→NT)

・T3 VETO

N: 20cm×100cm×5cm

T3: 10cm×100cm×2cm

T2: 4cm×16cm×0.6cm

charged particle identification
Charged particle identification

E VS. dE/dx

PID1

T2 energy loss (MeVee)

E VS. TOF

TOF (1/b)

Total E

PID2

d

TOF

p

PID2

p

e

dE/dx

PID1

Total E (MeVee)

comparison with e160

p

p

Comparison with E160

E160

E508

dE/dx&Etot

TOF&Etot

range&Etot

PID function

w/proton

w/pion

w/proton

Energy spectrum

proton asymmetry of 12 c and 11 b
Proton asymmetry of 12C and 11B

L

L

Excitation spectrum w/proton

KEK E369 data

Excitation spectrum of 12C is well

known from previous experiment

eliminate the contamination

such as QF event inside the gate

asymmetry parameter of mesonic decay
Asymmetry parameter of mesonic decay

L → p- + p

1/2

s

0

1/2

l =0,1

wave function:

-sinq

cosq

1

Angular distribution of decay proton

Asymmetry parameter

S : 88%、P : 12%

a = 0.64

one sasaki et al solution

N

N

S

W

N

p,K,s

L

aNM

p

One (Sasaki et al.) solution

p Ex.+ K Ex. + s Ex+D.Q.

Sasaki et al.

PRC71 (2005)035502

Experimental

value

Gn/Gp ratio

weak coupling constant ofs meson

Both Gn/Gp and aNM are consistent with experimental value.

p

slide29

PID window

PID2 ( TOF .vs. Etotal )

p gate

p gate

PID1 ( dE/dX .vs. Etotal )

(p+, pX) reaction

p or p

identification of hypernuclear formation

8000

s ~340psec

p

6000

4000

K

2000

0

-3

-2

-1

1

2

3

0

(ns)

K+

p+

T1

target

Identification of hypernuclear formation

Good p/K/p separation

Good p/K separation

0

200

400

600

800

1000

1200

(MeV/c2)

-800

-600

-400

-200

200

0

(mm)

neutron spectrum for 5 he

L

Neutron spectrum for 5He

Theory :

Garbarino et al.

PRC69 (2004)

054603

Theoretical calc.

Q / 2 = 76MeV

No peakingat half of

Q-value (76MeV)even 5ΛHe

suggested larger contribution of

LNN→NNN or FSI than theoretical prediction.

slide32

np- & nn- angular distribution (5ΛHe)

Back-to-back

Back-to-back

Gn/Gp ~ Nnn/ Nnp= 0.45±0.11±0.03

systematic error is mainly come from efficiency for neutron (6%) + acceptance(3%)

slide33

13

Coincidence Measurement (A=12)

En +Ep

n + p

Counts

En +En

12ΛC

n + n

Ep +Ep

p + p

qNN

cos

MeV

Gn/Gp ~ Nnn/ Nnp= 0.51±0.13±0.05

Analysis detail on Kim’s Poster

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