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奈良女子大学大学院　人間文化研究科　博士後期課程 3 年 複合現象科学専攻　高エネルギー物理学研究室 藤川　美幸希

Measurement of Branching Fraction and Time-dependent CP Asymmetry Parameters in B 0  K 0 p 0 De c ays. Introduction Experimental Apparatus Analysis Event Reconstruction Branching Fraction Measurement Time-dependent CP Analysis Summary . 奈良女子大学大学院　人間文化研究科　博士後期課程 3 年

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奈良女子大学大学院　人間文化研究科　博士後期課程 3 年 複合現象科学専攻　高エネルギー物理学研究室 藤川　美幸希

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  1. Measurement of Branching Fraction and Time-dependent CP Asymmetry Parametersin B0K0p0 Decays • Introduction • Experimental Apparatus • Analysis • Event Reconstruction • Branching Fraction Measurement • Time-dependent CP Analysis • Summary 奈良女子大学大学院　人間文化研究科　博士後期課程3年 複合現象科学専攻　高エネルギー物理学研究室 藤川　美幸希

  2. Introduction - CP violation Big Bang ＝ Matter Anti-matter Matter Anti-matter ≫ Present CP violation is one of the necessary condition to explain the baryon asymmetry in universe C (Charge conjugation) : P (Parity) : CP violation Asymmetry btw Particle and anti-particle 公聴会

  3. Introduction - CP violation • First observation of CP violationin neutral kaon system CP eigenvalue Short lifetime ： KSpp＋1 Long lifetime ： KLppp−1 • If CP is conserved, KLppis forbidden But… KL ppexperimentally observed J. H. Christenson et al. Phys. Rev. Lett. 13, 138 (1964) 公聴会

  4. Introduction - CKM matrix Kobayashi-Maskawa Theory Prog. Theor. Phys. 49, 652(1973) The 2008 Physics Nobel Prize • CP violation in Standard model can be explained • by 3 quark generations Irreducible complex phase ⇒can violate CP 公聴会

  5. Introduction - CKM matrix • Triangle lengths ⇒ large CP violation possible • Unitarity of CKM matrix ⇒ Related to B decays • Independent measurement for 3 lengths and • angles important for complete test of CKM model • or for search of new mechanism 公聴会

  6. Introduction – How to measure CPV in B0 system? • Two different amplitude is necessary to observe • CP violating phase • In B system, there is two sources of CP violation • Mixing induced CP violation • Direct CP violation Interference between B decays with and without mixing where fcp is CP eigenstate Example of fcp; J/yK0, K0p0,p+p-,,, 公聴会

  7. Introduction – Mixing-induced CP violation fCP ① B0 mixing ② B0 ① B fCP fCP ① ② ② B B fCP mixing Interference between B decays with and without mixing  Mixing-induced CP Violation 公聴会

  8. Introduction – Mixing-induced CP violation fCP fCP ① B0 B0 CP mixing mixing ② B0 B0 ① B fCP fCP ① ② ② B B fCP mixing Interference between B decays with and without mixing  Mixing-induced CP Violation 公聴会

  9. Introduction – Direct CP violation • Decay amplitudes: • CP violating asymmetry (ACP) is defined as: • A non-zero ACP requires the following 3 conditions: • more than 2 decay amplitudes • non-zero strong phase difference :I - j= ≠ 0 • non-zero weak phase difference : φi-φj = φ≠ 0  Direct CP Violation 公聴会

  10. Introduction –Direct + mixing-inducedCP violation 1 Physical Region -1 1 -1 B0K0p0case mixing-induced CP Violation parameter Direct CP Violation parameter Need to measure time-dependence 公聴会

  11. Introduction – Coherent B0B0 production fCP CP eigenstate Dz bg ~ 0.425 Flavour tag ;q (EPR paradox) BTag 公聴会

  12. Introduction – Status of CPV measurement in B0J/yK0 B0 tag _ B0 tag hep-ex/0608039, PRL Clear CP violation observed in mixing –induced CPV process bc transition B0J/yK0 B0-B0Mixing sin2f1= 0.642 ±0.031 (stat) ±0.017 (syst) A = 0.018 ±0.021 (stat) ±0.014 (syst) 公聴会

  13. Introduction – CP violation in B0K0p0 ? s b s KS b KS d d d d p0 d p0 d d d bs transition proceeds via second order decay process Penguin diagram in Standard Model Penguin diagram with new physics bs modes sensitive to New Physics 公聴会

  14. Introduction – CP violation in B0K0p0 B0J/yK0 bc bs 公聴会

  15. Introduction – Direct CP violation status Nature 452, 332-335(2008) B0K+p- B0K-p+ w/ 535MBB First evidence of direct CP violation in B system • ACP(B0K+p-) = –0.094±0.018±0.008 4.8s • ACP(B+K+p0) = + 0.07 ±0.03 ±0.01 公聴会

  16. Introduction – Prediction for direct CPV in B0K0p0 Isospin sum rule among BKp CP asymmetries M. Gronau, PLB 672(2005)82-88) Standard Model prediction • Prediction from SM • ACP(K0p0) =－0.148±0.044 • Breaking sum rule indicates • New Physics • Good test for Standard Model measurement 公聴会

  17. Experimental Apparatus KEKB Accelerator & Belle Detector

  18. KEKB Accelerator Belle Detector e- e+ • Why asymmetric collider? • Increase BB separation, • B flight length ～ 200mm 3km circumference 公聴会

  19. Performance of KEKB • Peak luminosity L = 1.7118×1034 /cm/s • Integrated Luminosity Integrated luminosity (fb-1) 2006 summer 605 fb-1＝657MBBpair year 公聴会

  20. Belle detector SC solenoid 1.5T Aerogel Cherenkov cnt. (ACC) CsI(Tl) Calorimeter (ECL) 3.5 GeV e+ Time of Flight (TOF) 8 GeVe- Central Drift Chamber (CDC) m/ KL detector (KLM) Si vtx. detector (SVD) 公聴会

  21. Belle sub-detector 公聴会

  22. SVD – Configuration • In summer 2003, SVD1 was replaced with SVD2 23º<q<139º SVD1 x-z plane 3 layers e+ e- SVD2 17º<q<150º 4 layers • First 152×106BB pairs collected with SVD1 • Remaining 505×106BB pairs collected with SVD2 公聴会

  23. Event Reconstruction

  24. Event Reconstruction B0K0p0 B0 KSp0 B0 KLp0 (mentioned later) 公聴会

  25. Event Reconstruction – KS two p angle should be small Long flight < 30 mrad IP 0.480 < m(p+p-) < 0.516 GeV/c2 0 KS is reconstructed from two charged p • Invariant mass • The smaller of dr1 and dr2, the shortest distance between the two KS daughter tracks and the IP (dr) • The azimuthal angle between the momentum vector and decay vertex vector of a KS candidate (df) • The distance between the two KS daughter tracks at their point of interception (z_dist) • The flight length of a KS candidate in the x-y plane (fl) 公聴会

  26. Event Reconstruction – p0 p0 reconstructed from two g • Eg > 50MeV in Barrel, Eg > 100MeV in End-cap region • Energy of photon • Invariant mass • Mass-constrained fit c2 • Angle between p0 in the B rest frame and g momentum in the p0 rest frame 0.115< M(p0 )<0.152 GeV/c2 • c2<50 • cosq <0.95 公聴会

  27. Event Reconstruction – B0KSp0 CMS : Υ(4S) rest frame Ebeam: Beam energy EB : Reconstructed B energy PB : Reconstructed B momentum 2 kinematic variables B0 e+ e- Y(4S) B0 Signal MC 公聴会

  28. Event Reconstruction – Continuum suppression e+e-U(4S)BB (Spherical) e+e- qq (Jet-like) Main background ⇒ continuum (e+e-qq) cosqB: polar angle of B in CMS Fox-Wolfram moments : Event shape variables Combine variables 0.3<LS/B signal retained : 91% background rejected : 71% 公聴会

  29. Event Reconstruction – B0 Signal 公聴会

  30. Branching Fraction Measurement

  31. Branching Fraction – Basic formula • Reconstruction efficiency obtained from Signal MC Consider difference between data and MC : • We use 657×106 BB events 公聴会

  32. Branching Fraction – Experimental Results • Mbc, DE, LS/B distribution from data How to estimation Signal yield? need to determine the signal shape & background shape 公聴会

  33. Branching Fraction – Signal PDF Probability Density Function • Mbc, DE, LS/B correlated • Can’t fit with 1D×1D×1D functions • Use 3D histogram PDF 公聴会

  34. Branching Fraction – BB background PDF • Mainly from BKpp, BK*p ,,, • Use 3D histogram PDF 公聴会

  35. Branching Fraction – Total PDF • qq background PDF • Total likelihood • Extended unbinned maximum likelihood fit • Free parameters • Branching Fraction( ), Nbkg • Argus shape, Poly1st shape • fqq 公聴会

  36. Branching Fraction – Fit result 　－0.15<DE<0.1 ; 0.7<L Signal yield ; 634±37 －0.15<DE<0.1 ; 5.27< Mbc <5.29 5.27 <Mbc <5.29 ; 0.7<L 公聴会

  37. Branching Fraction – Result + 0.51 + 0.46 B(B0K0p0)=[8.72 (stat) (syst)]×10－6 －0.50 －0.40 • Agree with current world average B(B0K0p0)=(9.8±0.6)×10－6 • Systematic Uncertainty 公聴会

  38. Time-dependent CP Analysis

  39. CP Analysis – Principle of Measurement Measured Dt True Dt D t (ps) Dt (ps) Evaluate CP asymmetry from the Dt and q fCP CP eigenstate Dz bg ~ 0.425 Flavour tag ;q • Smeared by • Detector resolution • Wrong flavor tag effect 公聴会

  40. CP Analysis – Vertex reconstruction p- p+ B decays vertices are reconstructed using the tracks coming from their decay particles using kinematical vertex fit. • IP (interaction point) tube constraint fit • No primary tracks from B vertex • Extrapolate KS track to the Interaction Point • Events without the vertex can still be used to measure A 公聴会

  41. CP Analysis – Flavour Tagging • For the BCP-Btag coherency originated from U(4S) decay, Btag flavour determines BCP flavour (B0 or B0) at Btag decay time. • Flavour information is determined from Btag decay products. • Inclusive Leptons: • high-p l • intermed-p l+ High-p l－　→　B0 High-p l＋　→　B0 K－　→　B0 K＋　→　B0 p－　→　B0 p＋　→　B0

  42. CP Analysis –Treatment of vertex resolution B B Dz [NIM A533: 370,2004] g p0 Bgen Brec g We understand the following resolution components: • Detector resolution: • Effect of non-primary particles: • Kinematic approximation of B0 flight: Residuals=Zrec ― Zgen Ks Tag-side only l Btag Non-primary particles D 公聴会

  43. CP Analysis – Maximum Likelihood fit 1 Background Signal Next slide Signal fraction Signal PDF Resolution Wrong flavor tag effect Maximum Likelihood Fit 公聴会

  44. CP Analysis – Maximum Likelihood fit 2 Background PDF qq Finite lifetime of D meson and short lived particles 5.20 < Mbc < 5.26 GeV/c2 0.05 < DE < 0.20 GeV Sideband region B+B- Charged B MC B0B0 Neutral B MC 公聴会

  45. CP Analysis – Inclusion of B0KLp0 • KLis detected by KLM hits and/or ECL hits • Cannot measure decay vertex of KLp0 • Time-integrated PDF is used to measure ACP Wrong flavor tag effect 公聴会

  46. CP Analysis – Final Results ACP = + 0.14±0.13(stat)±0.06(syst) SCP = + 0.67±0.31(stat)±0.08(syst) eff 公聴会

  47. CP Analysis – Systematic Uncertainty 公聴会

  48. Summary & Discussion

  49. Summary + 0.51 + 0.46 B(B0K0p0)=[8.72 (stat) (syst)]×10－6 －0.50 －0.40 We have measured Branching Fraction and Time-dependent CP Violation Parameters of B0K0p0 from 657×106 BB pairs ACP = + 0.14±0.13(stat)±0.06(syst) SCP = + 0.67±0.31(stat)±0.08(syst) eff • SCP ; Consistent with B0J/yK0 (bc transition modes) • ACP ; No evidence for direct CP violation 公聴会

  50. Discussion – Compare with other experiment Isospin sum rule expectation eff SCP BaBar 0.55 0.200.03 Belle 0.67 0.31 0.08 Average 0.57 0.17 CCP= － ACP BaBar 0.13 0.130.03 Belle - 0.14 0.13 0.06 Average 0.01  0.10 • Our ACP result ; 1.9s deviation from isospin sum rule 公聴会

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