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A study of charmless hadronic two-body B decays at Belle

A study of charmless hadronic two-body B decays at Belle. Nov 30, 2007 Yuuj ｉ Unno (Hanyang) HaengDang Symposium 2007 @Hanyang university. Contents. Introduction CP violation B Kπ, ππ, KK KEKB and Belle Analysis Kinematic reconstruction Continuum suppression Kπ separation

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A study of charmless hadronic two-body B decays at Belle

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  1. A study of charmless hadronic two-body B decays at Belle Nov 30, 2007 Yuujｉ Unno (Hanyang) HaengDang Symposium 2007 @Hanyang university.

  2. Contents • Introduction • CP violation • BKπ, ππ, KK • KEKB and Belle • Analysis • Kinematic reconstruction • Continuum suppression • Kπ separation • Results • Branching fractions • Partial rate CP asymmetry (Acp) • Summary HaengDang Symposium

  3. Introduction • We live in the universe dominated by matter. • The matter and anti-matter were created in the equal amounts • Where have the anti-matter gone??? • CP violation is one of the key to answer this mystery • Sakharov’s 3 conditions (1976) • (1) Baryon number violation • (2) Irreversible reaction • (3) CP violation (CPV) : CP = charge conjugation and parity transformation • CP conservation was believed for a long time • CPV was discovered in K system in 1964. • Kobayashi-Maskawa(KM) model (in 1973) can explain HaengDang Symposium

  4. +O(λ4) Introduction (KM model) KM model predicted the existence of 3 generations, 6 quarks. Weak interaction induces CP violation within the Standard Model(SM) Lagrangian of charged-current weak interaction • Weinberg-Salam theory • Quantum Chromo-dynamics CKM matrix Wolfenstein parameterization λ~0.2, A~O(1) CPV is due to a complex phase in quark mixing matrix CPV in K system was small ~ 0.1% Large CPV in B system!!! CP violation HaengDang Symposium

  5. Bππ BB mixing BJ/ψKs BKsπ0 bulv bclv BKπ Introduction (KM matrix and unitarity triangle) unitarity Unitarity triangle Test KM model is important. Precise measurements of 3 angles and 3 side lengths. B meson system is best field!!! HaengDang Symposium

  6. Introduction (CP violation in B system) (1) Mixing induced CP violation(ICPV) : Only neutral B Neutral B mix with box diagram Interference B0f and B0B0f leads CPV CPV from the mixing rate asymmetry. Decay time evolution info. Time-dependent analysis ICPV in the B0J/ψKs has been observed in 2001 at Belle. (2) Direct CP violation(DCPV) : Both charged and neutral B is possible Simple (^-^)! CPV in the decay process. NO time info. is necessary Time-integrated analysis Large DCPV in B system is predicted!!! But no observation yet. HaengDang Symposium

  7. Introduction (Direct CP violation) HaengDang Symposium

  8. Introduction (KM model and particle physics) History of CP Violation 1964: Discovery of CPV in K decays (Fithch & Cronin et al.) 1967: Role of CPV in the creation of the universe (Sakarov’s 3 conditions) 1973: Kobayashi-Makawa(KM) model  6 quark, CPV 1974: Discovery of charm quark (Ting, Richter et al.) 1979: Discovery of bottom quark (Lederman et al.) 1981: Predict large CPV in neutral B meson system (Bigi, Carter, Sanda) 1987: Discovery of large B0B0 mixing(ARGUS) 1995: Discovery of top quark (CDF, D0) 1999: Discovery of DCPV in K decays (KTeV, NA48) 2001: Discovery of ICPV in B decays (Belle, Babar) 20xx: Is next DCPV in B decays??? or New physics??? We are working on the KM prediction load HaengDang Symposium

  9. Introduction (Bhh : Kπ/ππ/KK) Charmless hadronic two-body B decays, BK+π-/K+π0/K0π0/K0π0/π+π-/π+π0/π0π0/K+K+/K+K0/K0K0 provides rich information for CPV, CKM angles, new physics, B decay dynamics. Tree Color supp. Tree W Exchange Annihilation Penguin Electro Weak Penguin Penguin Annihilation Color supp. EWPenguin Dominated by (bu Tree) and (bd, s Penguin) HaengDang Symposium

  10. Introduction (Bhh) New physics??? φ3 Penguin dominant modes are sensitive to new physics • DCPV through an interference between T and P • φ2 by B0π+π- time-dependent analysis • Sππ＝sin2(φ2+Θ)  isospin analysis in ππ system •  Br & Acp of π+π-, π+π0, π0π0 is important • Need to understand hadronic uncertainties with all Bhh • pQCD, QCD factorization, isospin, SU(3) symmetries,,,, • φ3extraction is theoretically challenging •  Coherent study of Bhh is important. •  Ratios of Br(Bhh) are very useful. HaengDang Symposium

  11. Introduction (Bhh) φ1 (and new physics search) from bs penguin modes Time dependent analysis φ2 measurement from Bπ＋π- Time dependent analysis Bhh Br & Acp （& φ３ & new physics search） from all Bhh Time integrated analysis HaengDang Symposium

  12. Introduction (KEKB accelerator) Y(4S)  BB many final states 3.5 GeV e- Belle 8.0GeV e+ • Ring length 3Km • Two separate ring for e+ and e- • Energy in CM is 10.58GeV • B factory : e+e- (4S)  BB (1.1nb) HaengDang Symposium

  13. Introduction (KEKB performance) • World record • Peak luminosity = 17.2 /nb/s • Integrated. luminosity. = 750 /fb •  corresponding ＞650 M BB pairs • BB pairs are accumulated, -- recent event rate =~ 400Hz -- σ(e+e-(4S)) = 1nb (400Hz)x(16.5/nb/s)x(1nb) =~ 66/s Integrated luminosity (/fb) • Today’s results are based on • 449or535M BB • (1.5 ~ 4 times larger than last pub.) HaengDang Symposium

  14. Introduction (Belle detector) Aerogel Cherenkov Counter Kπ separation Electromagnetic Calorimeter γ, π0 reconstruction e＋－, KL identification 3.5 GeV e＋ TOF Counter Kπ separation 8.0 GeV e — KLMuon Detector KL, μ detection Central Drift Chamber Charged track momentum Kπ separation Silicon Vertex Detector B vertex HaengDang Symposium

  15. 14 countries 55 institutes ~400 collaborators Introduction (Belle Collaboration) Seoul National U. Shinshu U. Sungkyunkwan U. U. of Sydney Tata Institute Toho U. Tohoku U. Tohuku Gakuin U. U. of Tokyo Tokyo Inst. of Tech. Tokyo Metropolitan U. Tokyo U. of Agri. and Tech. INFN Torino Toyama Nat’l College VPI Yonsei U. Nagoya U. Nara Women’s U. National Central U. National Taiwan U. National United U. Nihon Dental College Niigata U. Nova Gorica Osaka U. Osaka City U. Panjab U. Peking U. Princeton U. Riken Saga U. USTC BINP Chiba U. U. of Cincinnati Ewha Womans U. Fu-Jen Catholic U. U. of Giessen Gyeongsang Nat’l U. Hanyang U. U. of Hawaii Hiroshima Tech. IHEP, Beijing IHEP, Moscow IHEP, Vienna ITEP Kanagawa U. KEK Korea U. Krakow Inst. of Nucl. Phys. Kyoto U. Kyungpook Nat’l U. EPF Lausanne Jozef Stefan Inst. / U. of Ljubljana / U. of Maribor U. of Melbourne HaengDang Symposium

  16. Analysis Kinematical reconstruction Continuum(qq) background suppression Kπ separation Signal extraction Result HaengDang Symposium

  17. Analysis (kinematic reconstruction) • Charge track by CDC + SVD • K0K0Sπ+π- • π0γγ • B candidate with ΔE + mbc • signal • e+e-qq(q=udsc) • feed-acrros(pp⇔Kp) • charmless rare B(rp,K*p,,,) HaengDang Symposium

  18. Dominant background comes from e+e-  qq(q=udsc) continuum process Analysis (qq background suppression) Suppress background by mainly using event topology BB(σ~1nb) is spherical qq(σ~3nb) is jet-like • u ＜　0.1 GeV/c2 • d ＜　0.1 GeV/c2 • s ～ 0.1 GeV/c2 • c ～ 1 .25 GeV/c2 • B ～ 5 .28 GeV/c2 • Y(4S) ～10.58 GeV/c2 • Event topology is evaluated by • Fox-wolfram moment with fisher discriminant • Separate sig and bkg using likelihood method HaengDang Symposium

  19. Analysis (qq background suppression) Before cut on R After cut on R qq rejection power is ~90%, sig. eff. is ~70% for BKp mode HaengDang Symposium

  20. Analysis (Kπ separation) Ionization energy loss Cherenkov light yield Charged particle emit cherenkov light(transition radiation) if velocity is faster than that of light in material HaengDang Symposium

  21. Analysis (Kπ separation) ex) BK+π- selection Before cut After cut HaengDang Symposium

  22. Continuum Mbc : Argus func. ΔE : 2 cheby. func. B0K+π- Smoothed hist. of MC Charmless rare B Smoothed hist of MC B0π+π- Smoothed hist of MC Analysis (signal extraction) Unbinned maximum likelihood fit on ΔE and mbc • i = B candidate event • j = sig/rare/qq/feed accros • n = # of events • q = +1 or –1 for B or B tag • P = probability density func. Example (B0 K+π- ) HaengDang Symposium

  23. Branching fraction measurements HaengDang Symposium

  24. signal feed-across qq rare B Result of Br (signal extraction) K+π- π0π0 π+π- K+K- K+π0 K0K+ π+π0 K0π+ K0π0 K0K0 HaengDang Symposium

  25. Result of Br • Black 449MBB • Blue 535 MBB preliminary • Clear Br hierarchy can be seen. Kπ＞ππ＞KK • First observation of bd penguin K+K0 and K0K0 •  theoretical expectation (pQCD/QCDF) ~1x10-6 • Observation of π0π0 •  # of events is still small to measure Acp to constraint φ2 • Only missing is K+K- ultra-suppressed mode(W-exhange) HaengDang Symposium

  26. Result of Br (ratios of Br) = Rc = Rn • Rations of Br can reduce •  systematics of experimental results • hadronic uncertainty in theory calculation Discussions with theoretical predictions can be done HaengDang Symposium

  27. 449MBB 85MBB Result of Br (discussion on Kπpuzzle) A.J. Buras, R. Fleischer, et al., Phys. J. C 45, 701-710 (2006) We were/are here in Rc-Rn q = PEW effect φ=φ3 Kπ puzzle was vanished! HaengDang Symposium

  28. Partial rate asymmetry Acp HaengDang Symposium

  29. Result of Acp (signal extraction) B+K+π0 B0K+π- B+π+π0 B0π0π0 HaengDang Symposium

  30. B0K0K0 Result of Acp (signal extraction) B+K0π+ B+K0K+ HaengDang Symposium

  31. (K+p- = T + P) (K+p0 = T + P) Naïve theoretical expectation ΔAcp = Acp(K+π0)-Acp(K+π-)～0 Result of Acp • Black 449 MBB • Blue 535 MBB • Green 535 MBB • Time-dep. analysis Preliminary • Significant DCPV in K+π- and π+π- • DCPV in B meson system is now established • ΔAcp puzzle(?!) • ΔAcp = Acp(K+π0) - Acp(K+π-) = +0.164±0.037 4.4σ HaengDang Symposium

  32. Result of Acp (discussion on ΔAcp puzzle) K+π- K+π0 ΔAcp ~ 0 is expected by assuming low C and PEW • Enhancement of C ? •  C ~T or C＞T •  breakdown of theoretical understanding • Enhancement of PEW ? •  Would indicate new physics. • No theory within SM exist so far. • C.W.Chaing, et al., PRD 70, 034020 • Y.Y.Charng, et al., PRD 71, 014036 • W.S.Hou, et al., PRL 95, 141601 • S.Baek, et al., PRD 71, 057502 • S.Baek, et al., PLB 653, 249 • H.Li,et al., PRD 72, 114005 HaengDang Symposium

  33. Result of Acp (discussion on ΔAcp puzzle) • Further examination on ΔAcp puzzle • M. Gronau, PLB 672, 82-88 • A precise sum rule among four BKπ CP asymmetries • A violation of the sum rule would be evidence of new physics. • The sum rule predicts Acp(K0π0) = - 0.15±0.06 • Different(?!) from the prediction • δAcp(K0π0) is still too large to claim a discrepancy.  Have to examine this at Super-B stage HaengDang Symposium

  34. Summary • Study of Bhh plays significant roles • CPV search • CKM angle determination • New physics search • B decay dynamics understanding • Branching fraction measurements • Measure Br of all Bhh modes • Kπ puzzle was gone • First observations of bd penguin BKK0, K0K0 • Only missing is B0K+K-(W-exhange) • Acp measurements • Direct CP violation in B0K+π- and p+p- are established • ΔAcp puzzle is found with 4.4σ !!! • ΔAcp puzzlehave to be published ASAP… HaengDang Symposium

  35. Introduction (Bhh) HaengDang Symposium

  36. Systematics of Br(Bhh) Systematics of FSR is about 1.0% HaengDang Symposium

  37. Systematics of π0π0 Br=1.1±0.3±0.1 HaengDang Symposium

  38. Systematics of π0π0 • Why did Br(π0π0) decrease? • Main reason is just statistics fluctuation. • Second one is Good treatment of QED background. QED bkg is considered only in systematics • with 277MBB (last published data set) (New cut with new LR) (New cut with new LR) • with 535 MBB Good treatment of QED bkg decrease Br slightly HaengDang Symposium

  39. signal qq rare B Off time QED Acp(π0π0) HaengDang Symposium

  40. π0π0 : Off time QED background Time information Off-time events • Define • On -time • Off-time ~5.28GeV/c2 Bhabha events CsI trigger time cosΘ2 Emiss cosΘ1 HaengDang Symposium

  41. Systematics of Acp • detector bias of Kπ0,ππ0from qq bkg in (ΔE, mbc) • detector bias of Kπfrom D*+　D0(Kπ)π+ HaengDang Symposium

  42. Dominant background comes from e+e-  qq(q=udsc) continuum process Analysis (qq background suppression) (1) Event topology BB is spherical qq is jet-like  Modified Fox-wolfram moment with fisher discriminant Sig & non-Sig Non-sig & non-sig Transverse mom. 17 coefficients of fisher single variable HaengDang Symposium

  43. Analysis (qq background suppression) (2) cosqB : B flight direction (Jp conservation in decay) BB  1-cosqB vs qq  uniform (3) Likelihood approach KSFW qq rejection power is ~90%, sig. eff. is ~70% for BKp mode HaengDang Symposium

  44. Analysis (High momentum Kπ separation : KID) • D*+D0(K-p+)p+S • Very clean • can identify K andπ by pS Δm=m(D*+)-m(D0) Charge asymmetry bias is corrected in the signal extraction. HaengDang Symposium

  45. Analysis (KID correction: ex. B0K+p-) Belle KID has high performance BUT NOT PERFECT • Existence of KID charge asymmetry smears true Acp • Finite KID fake dilutes true Acp : K＋p- K-p+ To obtain true Acp, introduce KID correction B0K+p- : ~ -1% correction is applied HaengDang Symposium

  46. Flavor tagging b flavor information is needed for non-flavor-specific B0 modes Judge tag side B flavor with flavor specific processes  Charge of lepton / Kaon / slow-pion. NIM A 533, 516 (2004) Tagging efficiency is ~ 30 % HaengDang Symposium

  47. Simultaneous fit on B and B Analysis (Signal extraction) Signal extraction is performed with unbinned maximum likelihood fit on ΔE and mbc(or more). Likelihood is j = signal/rare/qq/feed accros q = +1 or –1 for B0 or B0 tag Xd= time-integrated mixing param. w = wrong tag fraction (mis-identification of flavor) (1)flavor specific modes(B+, B0K+π-) (2)other neutral B modes (3)π0π0 HaengDang Symposium

  48. Analysis (Signal extraction) • How to determine the PDF • (1) MC simulation • There is small correlation in ΔE and mbc, so, • Signal  smoothed histogram of MC • Feed-accros  smoothed histogram of MC • rare B  smoothed histogram of MC • continuum  Argus func.(mbc) & chebychev func(ΔE) • (2) Calibration • Detector response of MC is different from data. • PDF of MC is calibrated with • high statistics and similar kinematic control samples. HaengDang Symposium

  49. KEKB performance • Peak luminosity = 16.5 /nb/s • BB pairs are produced, Recent event rate =~ 400Hz σ(e+e-(4S)) = 1nb (400Hz)x(16.5/nb/s)x(1nb) =~ 66/s HaengDang Symposium

  50. signal qq rare B Off time QED Energy deposit in CsI Br(Bπ0π0) : signal extraction • Off timing QED background fake π0π0 • To distinguish, introduce 3 variables • cosΘ1 : high momentum π0 • cosΘ2 : low momentum π0 • Emiss : missing energy of other B • 5D(ΔE, mbc, cosΘ1, cosΘ2, Emiss) UML fit HaengDang Symposium

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