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Study of CP Violation in B 0  Ksπ 0 at Belle

ICEPP Symposium in Hakuba 2004/02/15. Study of CP Violation in B 0  Ksπ 0 at Belle. Niigata-University T.Shibata KEK T.Higuchi Taiwan-University K.F.Chen Belle Collaboration. Introduction to Ks π 0 Mode. u. s. π. 0. Ks. u. d. s. Ks. d. π.

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Study of CP Violation in B 0  Ksπ 0 at Belle

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  1. ICEPP Symposium in Hakuba 2004/02/15 Study of CP Violation in B0 Ksπ0 at Belle Niigata-University T.Shibata KEK T.Higuchi Taiwan-University K.F.Chen Belle Collaboration

  2. Introduction toKs π0 Mode

  3. u s π 0 Ks u d s Ks d π 0 d d d Ks π0 Mixing Indirect CP-Violation Mode likely JψKs  Dominant! Tree type Penguin type In Standard Model ≪ ( no phase )  Very Small Effect

  4. BaBar Result of LP03 s b s Ks d d π 0 d d Physical Motivation If New Physics in loop … Events=122±16 Ks π0 is sensitivity for new physics in loop diagram.

  5. Today’s TopicsEvent Selection & Signal Yield Analysis process B0 reconstruction (1)Event Selection (2) Signal & Background Yield Extraction CP-Fit Analysis (1) Define the Resolution of Δt for Ksπ0 mode (2) Δt & CP-Asymmetry Fitting

  6. KEK Event Selection Ks&π0 Selection B0 Reconstruction Vertex Reconstruction Background Rejection

  7. Data Sample for Analysis 140fb-1 ∫(Luminosity)dt = 140fb-1 #BB = 150×106 1999.5 2001.11 2003.7 Estimate Events Br( B0 Ksπ0 ) ～4×10-6 ( Physics Letters B407(1997)) ～400events Br( π0→ γ γ ) ～98.8% Efficiency=100% Br( Ks→ π+π- ) ～68.6%

  8. : Beam Energy : Energy of B : Momentum of B B0 Reconstruction Ks & π0 Selection Ks→ π+π- Beam Constrained Mass |Mππ–497.672| < 15MeV/c² π0→ γ γ 118< Mγγ<150 MeV/c² Energy Difference Ks Mass (MeV/c2) π0 Mass (MeV/c2) All of them are CMS

  9. Vertex Reconstruction Vertexing process 200μm p+ p- 3.0mm 2.7cm Calculate Ks Momentum B0 Vertex region Ks  e+ e- Vertex Fit used Ks with B0 Vertex region constrained B0 g g Ks π0 MC 103.6μm Vertexing efficiency B0Ks π0 : ε=25.9% B0J/ψ Ks : ε=95.8% (RMS) J/ψKs MC 55.6μm (RMS) (Not official value) True – Reconstructed ( μm )

  10. Background Rejection Main Background is Jet events ( e+e-qq )  Rejected used difference of Topology of events qq event B event 1 cosθij j 2 i 3 5 4 : Jet event Super Fox-Wolfram(SFW)( cosθij ) candidate B0 qq event B event cosθB θB Z (=beam direction ) cosθB

  11. Background Rejection Likelihood Likelihood Ratio Likelihood Ratio Cut L(SFW)=SFW shape L(cosθB)= cosθBshape LR>0.8 was defined as Cut by LR > 0.80 Select became Maximum Nsig,qq…#of signal,qq

  12. Signal Yield Extraction Tukuba hall in KEK

  13. Signal Yield is calculated byUnbinned Maximum Likelihood Fit to Mbc&ΔE Pbkg shape = Sideband data ΔE(GeV) Psig shape = Signal MC Mbc(GeV/c2) Signal Region 5.27<Mbc<5.29(GeV/c²) -0.15< ΔE < 0.10 (GeV)

  14. Data Data Fit(sig+bkg) Fit(sig+bkg) Fit(sig) Fit(sig) Fitting Result without(L) & with(R) Vertexing LR>0.80 LR>0.80 Signal Yield =92.8±11.3 Signal Yield =26.2±5.6

  15. Reconstruction Efficiency

  16. Reconstruction Efficiency was Calculated by Monte Carlo W/ Vertex Cut W/o Vertex Cut Not LR Cut 30.6 % 7.6% 18.8 % 4.7% LR>0.80 Cut Mbc & ΔE distribution Mbc(GeV/c2) ΔE(GeV)

  17. Summary Used data sample140fb-1 We could estimate the Ksπ0 events without vertexing (93), but vertex efficiency is very small(25%). The #events for CP-fit is 26.

  18. Future Plan Background Study by MC  Estimate peaking background Measurement CP-Asymmetry  Define the special ‘Δt’ Resolution, because this resolution is different from J/Ψ mode( Golden mode )  This is very difficult problem Finish until JPS(2004 Spring) ???

  19. Appendix

  20. LP03 Conference Physics Motivation Measurement by B0 Mixing Theoretical uncertain is Small in Standard Model Clean Mode for New Physics Belle Result sin2f1 (Belle 2003,140 fb-1) =0.733±0.057±0.028 +0.09 sin2φ1eff = -0.96 ±0.50 -0.11

  21. In Weak Interaction Particle  Anti-Patrticle CP transformation Introduction to CP-Violation(1) Dynamics of Physics = Lagrangian Lphysics = L + Lh.c

  22. Introduction to CP-Violation(2) CP Conservation & CP Violation • U*ub=Uub LH.C = Lcp = L  Particle = Antiparticle  CP Conservation (ii) U*ubUub LH.C Lcp L  Particle  Antiparticle  CP Violation Hermite CP

  23. Mixing Introduction to CP-Violation(3) Requirement for CP-Violation Observation 1) More than Two Decay Process 2) Current has complex phase ( CKM matrix ) B0 decay to CP eigenstate Interference !! If complex phase is included in Amplitude, it will appear in interference term.

  24. Introduction to CP-Violation(4) Time dependent B Wave function Time Dependent CP Violation in B-B Mixing Time Dependence & CP-Asymmetry

  25. Introduction to CP-Violation(5) Physical Region Afcp Sfcp

  26. Event Selection π0 Eγ>50MeV (No match with Charged track) Ks,π0 Selection Criteria 0.118< Mγγ<0.150(GeV/c²) Ks | Mππ – 497.672(MeV/c ²) | < 15MeV/c² Fang-san’s Cut Other Cut IF Both π tracks have SVD_zhit > 0  dz<2.0cm IF One of πtrack has SVD_zhit(1)>0  dr>0.1mm IF Both π track have no SVD_zhit  dΦ<2.0cm B0 Reconstruction

  27. 0.5 0.2 0.1 -0.15 -0.2 5.27 5.29 Background Rejection by Super Fox-Wolfram Super Fox-Wolfram (moment ) : B-Candidate Particle Fisher discriminant : Other Particle (charge&neutral) : Legendre Function α,β are optimized with Signal MC & Sideband Data

  28. Background Rejection by New Super Fox-Wolfram I used N-SFW in this Analysis Missing Mass

  29. N-SFW(2) Divide mm2 region into 7 region for correlation between SFW and mm2 Total Parameter = (11+5+1)  7 : Scalar sum of the transverse momentum

  30. 0.5 0.2 0.1 -0.15 -0.2 5.27 5.29 N-SFW(3) Optimized N-SFW K-SFW (7 Missing Mass region ) Unit = GeV/c2 7 Missing Mass Regions mm2<-0.5 Parameters are optimized with Signal MC & Sideband Data -0.5<mm2<0.3 0.3<mm2<1.0 1.0<mm2<2.0 2.0<mm2<3.0 3.0<mm2<6.0 6.0<mm2 Black …Signal Blue…Background

  31. Background Rejection Unused Slide(1) Threshold was defined byFigure of Merits Likelihood Ratio Cut Likelihood Likelihood Ratio LR at Max of F.o.M Likelihood Ratio Select Cut by LR > 0.80

  32. Background Rejection 6 r-regions ( r = Wrong tag fraction ) We want to use more events Even if LR<0.80 Second Likelihood Ratio Cut Likelihood Ratio Cut in 0< LR<0.80 0 0.8 1.0 Likelihood Ratio region Loose Cut : 0.4 < LR  0.8

  33. Fitting Function(Signal Shape) Signal Mbc : Single Gaussian Signal Shape is obtained from Signal MC Signal ΔE : Single Gaussian

  34. Fitting Function(Background Shape) Background Mbc : ARGUS function Background Shape is obtained from Sideband data Background ΔE : Chebyshev Function

  35. Fitting Result before(L) & after(R) Vertexing 0.4<LR<0.80 0.4<LR<0.80 Signal Yield =38.9±13.0 Signal Yield =1.4±5.5

  36. Reconstruction Efficinecy by MC Genhep Infomarion Used Signal MC( 200,000events ) Reconstruction efficiency ( Before & after Vertexing )

  37. p+ p- Ks track B vertex IP e+ e- p+ p- Ks track B vertex IP g g B0-Vertexing by Ks B0-J/ψ Vertexing process ( J/ψe+e- Short Lifetime ) B0J/ψ Ks sz (cm) <sz> = 46 mm 0.35(cm) B0-Ks Vertexing process ( Ks π+π- Long Lifetime ) sz (cm) B0Ks π0 0.35(cm)

  38. Measurement of CP-Asymmetry Unused Slide(2)

  39. CP-Fit Fitting ‘Δt’ distribution & Asymmetry which free parameter are Afcp & Sfcp J/Ψ mode presented at ICHEP2002 Free Parameters

  40. CP-fit : Resolution Function(1) Most important work is define a Resolution Function of ‘Δt’ Resolution Function = Response Function of Δt Resolution fucntion Δt Δt Input :P(Δt) Output P’(Δt) Resolution Function

  41. CP-fit : Resolution Function(2) Signal Probability Density Function P(Δt) include Resolution Function Background (qq) Probability Density Function Proper time difference include resolution function

  42. CP-fit : Resolution Function(3) Component of Resolution Function (1) Detector Resolution (2) Secondary Particle effect (3) Kinematic Approximation D π , D*π, D*ρ,D0 π,J/ψKs, J/ψK+ In Belle, Resolution Function Parameters are defined by B0 Lifetime Fitting by Unbinned Maximum likelihood fit used Control Sample.

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