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sin2 b : Status & Perspectives

sin2 b : Status & Perspectives. BaBar. Gerhard Raven NIKHEF & VU Amsterdam. CP from Interference of Mixing and Decay. decay. mixing. decay. B J/ y K S,L : dominated by single decay amplitude.  Theoretically clean way (~1%) to measure sin2 b.

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sin2 b : Status & Perspectives

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  1. sin2b: Status & Perspectives BaBar Gerhard Raven NIKHEF & VU Amsterdam

  2. CP from Interference of Mixing and Decay decay mixing decay BJ/yKS,L: dominated by single decay amplitude Theoretically clean way (~1%) to measuresin2b CP violation results from interference between decays with and without mixing Time-dependent CP asymmetry:

  3. Ingredients of the Measurements PEP-2 (SLAC) B-Flavor Tagging Exclusive B Meson Reconstruction Vertexing &Time DifferenceDetermination fflav: determine Dt resolution, mistag rates w, (Dmd, tB, …) fCP: measure CP asymmetries

  4. Available Samples before tagging and vertexing cuts B decays to flavor-specific final states Add Belle D*lnu here B decays to CP-eigenstates with charmonium Belle BaBar angular analysis(not shown)

  5. Flavour Tagging Belle: rank individual tags based on expected performance in 6 groups BaBar: rank according to ‘physics process’ (eg. Lepton tags, Kaon tags,…) with performance cuts (eg. Kaon I and Kaon II) Drop low performance tags, end up with 4 groups Mistag rates measured using control samples Babar: • D(*)p/r/a1 • Simultaneous fit with CP sample • Errors due to finite control sample size automatically included in statistical error Belle: • D*lv • Separate fit, propagate numbers to CP fit

  6. Doubly CKM suppressed decays on tag side B0 3. (4s)  B0 B0 system is antisymmetric in two B mesons 4. System evolves coherently in time B0 bu interference for tag-side B induces time-dependent effect, just like reco-side and thus not fully accounted for in measured mistag rates Long, Baak, Cahn, Kirkby hep-ex/0303030, submitted to PRD • Many BDX modes have, at O(10-4), intrinsic “mistagging” due to bu transitions. Effect usually assumed to be • Small • Accounted for by measured mistag rates • On reco-side this bu interference can be used for sin(2 + ) measurement. Induces time-dependent effects of order |VubVcd/VcbVud|= 0.02 • Lepton tags unaffected, but eg. Kaon based tags are • For BaBar: Qlep ~0.1, Qnonlep ~0.2 • Small effect on sin(2b), larger on |l|; last BaBar result: • sDCSD(sin2b)= 0.008 (cmp to total syst: 0.034) • sDCSD(|l|) = 0.024 (cmp to total syst: 0.030)

  7. Results N(BB)= 88 106 N(BB)= 85 106 Note that the experiments also agree on color codes for B and B tags PRL 89 (2002) 201802 PRD 66 (2002) 071102 Belle BaBar

  8. Extrapolation: Luminosity Belle/KEK-B BaBar/PEP II Belle/KEK-B SVD2 installation Both experiments expect ~500/fb by 2006

  9. Extrapolation: Some History… a b c d e • “Osaka 2000” measurement. • (hep-ex/0008048). • Only J/y KS and y(2s) KS. • 1st Paper (PRL 86 (2001) 2515). • Added J/y KL. • Simultaneous sin2b and mixing fit. • 2nd Paper (PRL 87 (2001) 091801). • Added J/y K*0 and c KS. • Better vertexing. • Better SVT alignment and higher KS efficiency for new data. • Winter 2002 (hep-ex/0203007). • Improved event selection. • Reprocessed 1st 20 fb-1. • e) 3rd Paper (PRL 89 (2002) 201802 ) • Improved flavor tagging. • One more CP mode: hcKS. BaBar Statistical Systematic sin 2b uncertainties So far seem to do better than extrapolations predict

  10. Extrapolation: Belle Next B factory KEKB PEPII Expected errors in ACP’s Goals for July 2005: 315 /fb Stat. error ~0.04 Syst. error ~0.02 Goals for July 2007: 1000 /fb Stat. error ~0.02 Syst. error ~0.01 Will require a lot of hard work to get there!

  11. Extrapolation: BaBar Current analysis Clean modes Only lepton tags “Probably somewhat conservative…”

  12. The assumptions… • Mixing • Decay

  13. Back to basics: Flavour Mixing Effective Hamiltonian: Eigenstates: With mass & lifetime differences: , with • Assumptions made: • CPT conserved • no CP in mixing • DG=0 Note: if CPT and DG=0 => q/p is pure phase

  14. CP in mixing: experiment • Measure aSL using dileptons • aSL=0.51.2(stat)1.4(syst) • New analysis: • Simultaneous fit to time-dependence of both fully reconstructed CP and flavour eigenstates, tagged and untagged • Include • Detector charge asymmetries • Doubly-CKM suppressed decays PRL 88 (2002) 231808 preliminary • Started testing the assumptions that • CPT is conserved • DG/G is negligible • q/p is a pure phase • Nothing unexpected seen, will need MUCH • more data to approach SM prediction

  15. Back to basics: CP in decay BaBar Phys. Rev. D-RC 65 (2001) (20/fb) KEK Preprint 2002-9 (29/fb)) • Experiment: Look for direct CP in J/yK+ Leading penguin contribution has same weak phase as tree Expect very little direct CP

  16. Are (sin2b)J/yKs and (sin2b)J/yKLthe same? BaBar ? For B  J/yK*0(K-p+) : CC, S  S, ll Need K0—K0 bar mixing for interference in J/y KS and J/y KL CP violation in K0—K0 bar mixing: negligible Following Grossman, Kagan & LigetiPhys. Lett. B538 (2002) 327 Measure “wrong flavour” amplitude in BJ/y K*0(K+p-) Very much consistent with SM expectation of 0

  17. Other Modes Angular analysis, cos(2b) Color+Cabibbo suppressed tree + penguin b  s penguin b  s penguin + CKM suppressed tree bd Cabibbo suppressed tree + penguin, angular analysis Cabibbo suppressed tree + non-CP eigenstate

  18. J/yK*(KSp0) and cos(2b) O 1D: Treat R as dilution  2D: Use qtr 4D: Full angular analysis ±0.7 (syst) ±0.7 (syst) BaBar Belle Vector-Vector mode; Angular components: • A|| ,A0 : CP = +1 • A : CP = -1 (define R = |A|2 ) • Simplest method: • CP asymmetry diluted by D = (1 - 2R) • R = (16.0 ± 3.2 ± 1.4) % BaBar, PRL87 (2001) 241801 • R = (19 ± 2 ± 3) % Belle, PLB538 (2002) 11-20 Full angular distribution is given by: So at first sight should be able to determine cos(2b) and resolve some of the ambiguities in b Unfortunately there is an ambiguity:

  19. BJ/yp0 Nsig=407 hep-ex/0207058 hep-ex/0207098 tree: color- and Cabibbo-suppressed penguin: competing weak phase? In the absence of penguins, S=-sin(2b) and C=0

  20. Penguin Modes: BfKS Belle BaBar • Same CKM factors enter as J/yKS. • u-penguin CKM suppressed by ~0.02. • Unlike J/yKS, the leading and u-penguin amplitudes are both penguins. • Can use SU(3) related modes fp+ and K*K+ to experimentally bound u-penguin amplitude. • Grossman et al, hep-ph/9708305. • Current estimate of SM “pollution” on the assumption internal penguin flavor-singlet penguin PRD 67, 031102(R) (2003) is <5 % Add Br, # of signal events

  21. Penguin Modes: Bh’KS , f • Very similar to fKS except for one additional complication – a tree-level bu contribution. • London and Soni estimate the relative size of the bu tree to be |T/P|<0.02 (hep-ph/9704277) • Beneke and Neubert estimate |T/P|  (8  3)% (hep-ph/0210085) • Rough estimate for SM pollution is same as fKS although this is probably somewhat less conservative. Belle PRD 67, 031102(R) (2003) BaBar Belle Add Br, # of signal events

  22. Penguin Modes: -hCPS=sin(2b) ? “bs penguin” average Babar and Belle 0.18  0.20 About 2.5 s below golden modes! c2/Ndof = 4.8 / 4 Caveat: averaging fKS and h’KS assumes the b->u tree contribution in h’KS is negligible ’ h’Ks BaBar 0.02  0.34  0.03 Belle 0.71  0.37 (+0.05) Ave 0.34  0.25 –0.06 fKs BaBar –0.19 (+0.52)  0.09 Belle –0.73  0.64  0.22 Ave –0.39  0.41 –0.50 K+K-Ks non-resonant Belle 0.49  0.43  0.11 (+0.33) –0.00

  23. Penguin Modes: C = 0 ? h’Ks BaBar 0.10  0.22  0.03 Belle –0.26  0.22  0.03 Ave –0.08  0.16 fKs BaBar –0.80  0.38  0.12 Belle 0.56  0.41  0.16 Ave –0.19  0.30 K+K-Ks non-resonant Belle 0.40  0.33  0.10 (+0.26) “bs penguin” average “C” Babar and Belle –0.03  0.13

  24. Tree vs. Penguin: B D*+D- b  d penguin Cabibbo-suppressed tree PRL 89, 122001 (2002) Belle Note: not a CP eigenstate Gronau PRL 63, 1451 (’89) PLB 233, 479 (’89) BaBar BaBar If penguins negligible, C=0, S=-sin(2b)

  25. B D*D* Belle Belle Mostly CP-even BaBar Vector-Vector mode. since RT ~ 0 angular analysis not really needed

  26. Summary See also http://www.slac.stanford.edu/xorg/hfag/triangle/winter2003/index.shtml • Time dependent CP fits @ B factories have reached • maturity • sin(2b) measurement with charmonium KS,L well • established, • Starting to explore other (rare) modes, but • …need more data! Thanks to: Riccardo Faccini Yoshi Sakai Owen Long Gautier Hamel de Monchenault Andreas Hoecker

  27. Summary • Time dependent CP fits @ B factories have reached maturity • sin(2b) measurement with charmonium well established, • Consistent with constraint from indirect measurement • no longer limiting factor on CKM analysis • Starting to explore other (rare) modes, but • …need more data! Thanks to: Riccardo Faccini Yoshi Sakai Owen Long Gautier Hamel de Monchenault Andreas Hoecker See also http://www.slac.stanford.edu/xorg/hfag/triangle/winter2003/index.shtml

  28. BACKUP SLIDES

  29. Details: from Dz to Dt Boost Approximation 0.2% effect Improved Boost Approximation Average tB Approximation • Improves resolution by 5% in quadrature • If not used, resolution depends on |Dt| Proper time difference:

  30. Penguin Modes: the data… Belle hep-ex/0212062 Submitted to PRD BaBar hep-ex/0207070

  31. Yields (BaBar) BaBar

  32. Tagging Performance

  33. Control Samples No asymmetry observed as expected

  34. Systematic Errors for sin(2b) Total from winter 2002 result (56 fb-1) was 0.035 • Largest source comes from backgrounds • CP of Argus BG is zero in default fit. Attempt to fit for it in SB. Difference is systematic (very conservative). • Klong BG contributions • Composition of J/yX BG : 0.007 • Shape/reslution of DE : 0.007 • Some improvements over last iteration • Switched from PDG 2000 to PDG 2002 for B lifetime and Dmd. PDG uncertainties down by x2 (thanks to us). Both were 0.010 last time. • Peaking BG now split by mode. J/yKs has the lowest (0.3%, others >1.2%). Was 0.013, now 0.007. • MC bias correction (or MC statistics). Used x7 more MC this time. We understand part of the bias. Was 0.014, now 0.010.

  35. Dt reconstruction BREC direction BREC Vertex BREC daughters Interaction Point Beam spot TAG Vertex z BTAG direction TAG tracks, V0s • Reconstruct Brec vertex fromcharged Brec daughters • Determine BTag vertex from • All charged tracks not in Brec • Constrain with Brec vertex, beam spot, and (4S) momentum • Remove high c2 tracks (to reject charm decays) • High efficiency: 95% • Average Dz resolution ~ 180 mm (dominated by BTag) (<|Dz|> ~ 260 mm) • Dt resolution function measured from data

  36. Lepton tag only (cc)KSwith lepton tag Ntagged = 220 Purity = 98% Mistag fraction 3.3% sDt 20% better than other tag categories sin2b = 0.79  0.11

  37. Belle b->s penguin

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