1 B 中間子による量子もつれの検証 Y.Sakai KEK ( submitted to PRL quant-ph/ ) 金茶会 6-July-2007 One of “Exotic” topics of Belle Results 物理的背景と解析・結果

2 KEKB ~1 km in diameter Mt. Tsukuba KEKB Belle e + source Ares RF cavity Belle detector 8 GeV e - x 3.5 GeV e + L peak = 1.71x10 34 Integ. Lum. ~700 fb -1 PEP-II for BaBar KEKB for Belle ~700 fb -1 ~440 fb -1 Integrated Luminosity

3 Belle Detector K L  detector 14/15 layer RPC+Fe Electromagnetic Calorimeter CsI(Tl) 16X 0 Aerogel Cherenkov Counter n = 1.015~1.030 Si Vertex Detector 4-layer DSSD TOF counter 3.5 GeV e + Central Drift Chamber momentum, dE/dx 50-layers + He/C 2 H 6 charged particle tracking K/  separation B vertex Muon / K L identification ,  0 reconstruction e +-, K L identification 8.0 GeV e - 13 countries, 55 institutes, ~400 collaborators

4 EPR Entanglement EPR Paradox: Quantum Mechanics: Entangled state  non-separable wave function even for far apart particles can not be a “complete” theory Local realistic theory with “hidden” parameters AB “an element corresponding to each element of reality”

5 Bohm: Entangled states [Gedanken experiment] [D.Bohm., Quantum Theory, p614(1951)] two spin ½ particles from singlet state Measurement: S x =+1/2 for a  predict S x =  1/2 for b Decision of orientation of polarizer at very last moment  still above happen  No causal connection QM Instantaneous communication ? (  Quantum communication) Hidden parameters (Local Realistic Theory) ?

6 Bell Inequality Any Local realistic theory with “hidden” parameters S = |E(a,b)  E(a’,b)| + |E(a,b’)+E(a’,b’)| < 2 (Bell-CHSH Inequality) Violation  Reject LRT, Confirm QM J.S.Bell, Physics 1, 195(1964); Clauser,Horene, Shimony, Holt, PRL 23, 880(1969) Many experiments performed: loopholes - Locality: need space-like measurements of A and B - Detection efficiency: sub-sample  all Key for experimental check ! AB E(a,b): correlation function between measurements a and b Bell Inequality Violation = QM: ~established

7 Bell Inequality: exp. (1) Entangled photons [e.g. G.Weihs et al., PRL 81, 5039(1998)] (Locality loophole) A,B: 400m away, measurements <<1.3  s

8 S QM:max A:  ’= 0, 45 deg B:  ’= 22.5, 67.5 deg S = 2.73  coincidence Bell Ineq. is violated ! E(  )= C ++ + C   C   C   tot C xx : # of coincidence Efficiency ~5%

9 Bell Inequality: exp. (2) Entangled 9 Be + ions [e.g. M.A.Rowe et al., Nature 409, 791(2001)] (Detection efficiency loophole) E(     ) N sam  N dif N sam  N dif = ( )( )  ~98%

10      =        =   S = 2.25  0.03 Bell Ineq. is violated ! Detect photons by PMT

11 Why Y(4S)  B 0 B 0 System One of few entangled systems in HEP Highest energy scale (~10 GeV) breakdown of QM at high energy ? One of few entangled systems in HEP Highest energy scale (~10 GeV) breakdown of QM at high energy ? _ _ QM: Initial: B 0 B0B0 B0B0 _ B0B0 B0B0 ー [C=  1] + B 0 B 0 mixing _

12 Y(4S)  B 0 B 0 System _ _ QM: S ame F lavor (B 0 B 0, B 0 B 0 ): ∝ e  t| [1 + cos(  m  t)] O pposite F lavor (B 0 B 0 ) : ∝ e  t| [1  cos(  m  t)] A QM (  t) = OF  SF OF+SF = cos(  m  t) __ _ Joint Probability (  t=t 1  t 2 ) at t 1  t 2, B 0 B 0 or B 0 B 0 only _ _

13 Y(4S)  B 0 B 0 System _ _ Bell Inequality Test ? A QM (  t) = cos(  m  t) E(a,b) = cos(  m  t) ? curve a : same as “Entangled photons” or E(a,b) = - e  t’ e  t cos(  m  t) ? [includes decay rate] curve b a b ( t’ = Min(t a -t b ) )

14 Y(4S)  B 0 B 0 System Bell Inequality Test : intrinsically impossible QM to violate Bell Inequality ; x =  m/  > 2.6  x d = 0.78 Active measurement needed  Flavor measurement via decay reconstruction = passive [A.Bertlmann et al., PL A332, 355(2004)] Any way to test QM at Y(4S) ? _ _ Curve b should be taken [ some arguments may exist against above ]

15 Belle’s Approach Precise measurement of Time-dependent Flavor Correlation QM: A QM (  t) = OF  SF OF+SF = cos(  m  t) Quantitative proof of QM Entanglement Quantitative Comparison with Non-QM model Fully corrected (= true) A(  t)  Direct comparison with (any) theories Quantitative proof of QM Entanglement Quantitative Comparison with Non-QM model Fully corrected (= true) A(  t)  Direct comparison with (any) theories

16 Non-QM models Local Realism: Pompili & Selleri (PS) “elements of reality” (hidden variables) = Flavor & mass (B H, B L, B H, B L ) _ Mass states: stable random jump of Flavor within pair Single B 0 : oscillation ~ 1  cos(  mt) (example 1) [EPJ C14,469(2004)] only determine upper/lower limits of A(t 1,t 2 )

17 A(  t): PS model Integrated over t min Note) Local realistic model with same A(  t) as QM is possible [quant-ph/ ]

18 Non-QM models Spontaneous immediate Disentanglement (SD) (example 2) [e.g. PR 49,393(1936)] Integrated over t 1 +t 2 separates into B 0 & B 0 evolve independently _

19 Analysis Method B 0  D *  l  + Lepton-tag Fully corrected (= true) A(  t)  Quantitative Test for non-QM model Background subtraction Unfolding (detector resolution) OF & SF  t distribution ~Same as  m measurement ( high quality lepton-tag only) [PRL,89,251,803(02),PRD 71,972003(05)] Reconstruction Vertexing:  t =  z/c 

20 Signal Reconstruction signal background 6718 OF 1847 SF 6718 OF 1847 SF 152M BB Background subtraction of fake D*

21 Background Subtraction Bin-by-bin (  t ) for OF & SF  t (ps) 152M BB OF SF  Continuum : use off-Res. (negligible) Fake D*: M(D*)  M(D 0 ) sideband Combinatoric D*l : “reversed l” method B +  D **0 l : MC Wrong-tag correction : 1.5  0.5% (MC,data)

22 Unfolding (Deconvolution) Singular Value Decomposition (SVD) method [A.Hoecker, V.KKartvelishvile NIM A372, 469(1996)] Measured  t distribution True  t distribution Detector effect 11  t bins: 11 x 11 Response Matrix OF, SF separately (using MC) Matrix inversion  t Resolution Data/MC difference included  Robustness against input: checked by Toy MC  Sys. error (measured) = R x (true)

23 Cross Check: Lifetime Fully corrected OF+SF: fit with e  t/   =  0.017(stat) ps  consistent with PDG  2 = 3/11 bins (1.530  ps)

24 Results & Sys. errors Fully corrected A(  t) Systematic Errors stat. ~ sys.

25 Results & fit with QM  2 = 5.2 (11 dof) Good ! [ fit including WA  m = (0.496  0.014) ps -1 (excl. Belle/BaBar)] [quant-ph/ , submitted to PRL] 152M BB Fully corrected A(  t): fit with QM  m = (0.501  0.009) ps -1

26 Result: PS model  2 = 31.3 disfavored 5.1  over QM 152M BB PS Best Fit (error from  m) difference btw. Data/Fit (points not used if PS min < Data < PS max )  m = (0.447  0.010) ps -1

27 Result: SD model  2 = 174 disfavored 13  over QM Decoherence fraction: Fit (1-  )A QM +  A SD :  =  M BB SD Best Fit (error from  m) difference btw. Data/Fit  m = (0.419  0.008) ps -1 cf) K 0 K 0 system [CPLEAR, PLB 422, 339(1998) KLOE, PLB 642, 315 (2006)] _

28 Summary Quantitative study of EPR-type Flavor entanglement in Y(4S)  B 0 B 0 decays has been performed Quantitative study of EPR-type Flavor entanglement in Y(4S)  B 0 B 0 decays has been performed Fully corrected A(  t) measurement  allow Direct comparison with any theory Fully corrected A(  t) measurement  allow Direct comparison with any theory QM Entanglement : confirmed Pompili-Selleri type (Local Realism) model : disfavored by 5.1  Spontaneous Disentanglement: rejected by 13  _ Bell Inequality Test might be reconsidered ?

29 K 0 system EPR: CPLEAR A = OF  SF OS+SF p p  K 0 K 0 at rest (J PC ~1  ) _ _ [PLB 422,339 (1998)]  + K  (K-id by dE/dx)  = 0.40  0.7 [PRD 60, (1999)] Decoherence fraction in K 0 K 0 basis _ OF SF OF SF  t=0  t=5 cm

30 K 0 system EPR: KLOE [PLB 642,315(2006)] KLOE at DAPHNE (  Factory)   K S K L  (     )(     ) CPV decay Fit to  t distribution including regeneration Decoherence fraction in K 0 K 0 basis  = (0.10  0.21  0.04)x10 -5 _ 380pb -1 Decoherence: CP allowed decay   K S K S

31 Time-dependent Asymmetry