1. Polarimeters for Tests of EPR Paradox
Kentaro Yako
PST05
Nov. 15, 2005
Topics:
・ Bell’s Inequality in Spin Correlation of 2N systems
・ Proton Polarimeter, EPOL
・ Neutron Polarimeter, NPOL
→　poster presentation by S. Noji & K. Miki

2. Collaborators: T. Saito, H. Sakai, T. Kawabata, T. Ikeda, K. Itoh,
H. Kuboki, Y. Maeda, N. Matsui, H. Matsubara,
K. Miki, S. Noji, M. Sasano, Y. Satou,K. Sekiguchi,
K. Suda, A. Tamii, and T. Uesaka

3. EPR paradox Einstein, Podolsky and Rosen (1935):
Quantum mechanics (QM) is incomplete in terms of local realism.
“Paradox”. Hidden variables? b a
Particle 2
[1S0]
Particle 1
Polarimeter B
Polarimeter A
entangled state QM
EPR or

4. Test of Bell’s inequality by spin correlation measurement
J.S. Bell (1964):
Any local hidden variable theory contradicts QM. b a
Particle 2
[1S0]
Particle 1
Polarimeter B
Polarimeter A θ C a b
Spin correlation function
Bell’s inequality QM -1 20 40 60 80
θ (degrees)

5. Our experiment Spin correlation in 1S0 p-p (2He) system
・ Production of 2He by (d,2He) reaction
Two protons in one polarimeter
Good figure of merit & 2-proton tracking capability
→　EPOL

6. Polarimetry of EPOL Inclusive p + 12C scattering
Left / Right - asymmetry
Figure of Merit
: analyzing power (Ep,θ)
135 MeV
McNaughton et al.
Analyzer target

7. RIKEN Accelerator Facility
AVF
K = 540 MeV
Ed = 270 MeV
Ring
Cyclotron
SMART
SMART
EPOL
EPOL

8. Production of 2He at SMART
EPOL F2
2He production:
1H(d,2He)n reaction
at 0 deg
Td = 270 MeV
2nd focal plane of SMART
high purity 　　　
～98%
In abundance　
2x103 pairs / s
(0.3 nA, 100 mg/cm2)
±2%
10 msr
50H x 10V cm2
Focal plane size

9. Proton polarimeter EPOL
・ Analyzer target :
Carbon block 5 cmt
・Trigger signals,
charge information :
Plastic scintilators
HOD1, HOD2
・Trajectory before and
after analyzer:
Before
After
: MWDC#1
4 x (XUV)
: MWDC#2,
1 x (UV)
MWDC#3
4 x (XY) Y U X
・Angular acceptance :
θ < 20 deg V

10. Multi wire drift chambers
・ cell structure:
(MWDC#1)
・ operation gas :
Ar(50%) + Ethane(50%)
・ cathode and potential voltage: －2.7 kV
・ number of sense wires: 320 (#1) + 96 (#2) (#3) = 800
・ readout : LeCroy2735DC – LeCroyTDC3377
・ position resolution: ～0.2 mm
・ efficiency : 96～99% / plane

11. Calibration of EPOL Beams Ay(θ) Energy dependence θc.m. (deg) ・ beam
H.O. Meyer et al.,
PRC 27, 459 (1983)
Primary beam is unavailable
Secondary beam :
… p + 12C elastic scattering
Time reversal
→ induced polarization P = Ay
Ep = 160 MeV
at θ = 19o
Py = 0.943±0.013
・　Unpolarized p beam
→ eliminate the
false asymmetry
Ay(θ)
Energy dependence
・ Energy degraders (brass)
θc.m. (deg)
EPOL較正

12. Spin precession Spin precession C target Swinger EPOL SMART
Energy Degrader
EPOL
SMART
Ep (MeV) Degrader (mm) FP2
EPOL較正

13. Spectra with degrader

14. Effective Ay of EPOL Sector Results at Ep = 120～160 MeV AC = 0.11～0.30
εds = 2.8～4.7%
FOM = (0.7～2.6) x 10-3 結果

15. Two-ray tracking efficiency
Hit in the same cell
… efficiency becomes low.
analysis of
x-position …OK.
y-position …difficult ・
|y(1)－y(2)| > 20 mm
on Carbon target
x 0.70 ・
Two-ray tracking
x 0.79
Total effieicncy
0.55
|y(1)－y(2)| (mm)
イベント選択

16. Summary
To test Bell’s inequality by measuring C(θ) in two-proton system, we constructed a focal plane polarimeter, EPOL, at SMART at RIKEN.
EPOL was calibrated at 120ー160 MeV by using polarized protons produced by p+C elastic scattering:
EPOL is capable of measuring two-proton’s polarization simultaneously. Two-ray tracking efficiency is ～0.55.
AC = 0.11～0.30
εds = 2.8～4.7%
FOM = (0.7～2.6) x 10-3

17. Spin correlation function

18. Result of spin correlation measurement
Bell’s inequality is violated by 2.9 standard deviations.
Sakai et al., submitted to Nature Physics

19. EPR correlation in n-p system … NPOL
2H target
NPOL
n(TOF) p
EPOL
np[1S0]
SMART
2H(d,d*)d*
d* : pn 系が[1S0]に結合した状態

20. RIKEN NPOL