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Studying CP Asymmetries at the B Factories: Progress and Prospects

Studying CP Asymmetries at the B Factories: Progress and Prospects. Cornell HEP Seminar (Journal Club) October 15, 2002. Patricia Burchat Stanford University. Outline. The B Factories - performance Time-dependent CP-violating asymmetries CP charge asymmetries B hadronic decay rates.

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Studying CP Asymmetries at the B Factories: Progress and Prospects

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  1. Studying CP Asymmetries at the B Factories: Progress and Prospects Cornell HEP Seminar (Journal Club) October 15, 2002 Patricia Burchat Stanford University

  2. Outline • The B Factories - performance • Time-dependent CP-violating asymmetries • CP charge asymmetries • B hadronic decay rates Motivation for measurements. How well have we measured these properties? What have we learned? Patricia Burchat, Stanford

  3. BABAR/PEP-II peak luminosity: 4.6 x 1033cm-2s-1 (~5 BB/s) max lumi/24h: 309 pb-1 4.5-month shutdown started July 1, 2002 total recorded lumi to date: 94 fb-1 (~10% off-peak) Belle/KEK-B peak luminosity: 7.3 x 1033cm-2s-1 (~8 BB/s) max lumi/24h: 399 pb-1 2-month shutdown started July 1, 2002. Running now… total recorded lumi as of 10/14: ~96 fb-1 (~10% off-peak) The B Factory Experiments • c.f. integrated luminosity for • Argus (1983-1987): ~100 pb-1 • CLEO (1981-2000): ~16 fb-1 Patricia Burchat, Stanford

  4. d s b u c t The Unitarity Triangles (K system) d•s* = 0 (Bs system) s•b* = 0 (Bd system) d•b* = 0 These three triangles (and the three triangles corresponding to the rows) all have the same area. A nonzero area is a measure of CP violation and is an invariant of the CKM matrix. apply unitarity constraint to pairs of columns Patricia Burchat, Stanford

  5. d s b u c t The Unitarity Triangle Vtb*Vtd Vub*Vud a b g Vcb*Vcd Orientation of triangle has no physical significance. Only relative angle between sides is significant. apply unitarity constraint to these two columns Patricia Burchat, Stanford

  6. d s b u c t The Unitarity Triangle (r,h) Vtb*Vtd Vcb*Vcd Vub*Vud Vcb*Vcd a b g (1,0) (0,0) apply unitarity constraint to these two columns Patricia Burchat, Stanford

  7. i f i f CP A1 + A2 2 |A2| exp(id2) exp(iq2) -2 d2 d2 A1 + A2 exp(-2i2) |A1| exp(id1) exp(i1) P(if) - P(if) 2 |A1A2| sin(d1 - d2) sin(1 - 2)  Suppose i is a phase that does change sign under CP; di is a phase that does not change sign under CP. A1 = |A1| exp(i1) exp(i1) |A1| exp(i1) exp( - i1) A2 = |A2| exp(i2) exp(i2) |A2| exp(i2) exp( - i2) In figure below, phase convention for fields is chosen such that d1 = 1 = 0.  CP-violating differences between the decay rates of a particle and that of its antiparticle can arise from the interference between two decay amplitudes with relative CP-violating and non-CP-violating phases. Patricia Burchat, Stanford

  8. Meson mixing provides a source of error-free non-CKM phase shift by 90o ( i): |B0 (t)  cos(Dm t/2) |B0 – i sin(Dm t/2) |B0 exp(2if), where the CKM angle f is associated with the mixing box diagram. The phase in the CKM quark mixing matrix can provide a “CP-violating” phase. Interference between two decay diagrams (e.g., tree and penguin amplitudes with different CKM phases) can lead to CP-violating asymmetries but interpretation depends on relative strong phase. Patricia Burchat, Stanford DK

  9. p+ p— B0 / B0 e - e + e ±, m ±, K± tag Dz B0 / B0 Dz ~ 255 mm for PEP-II: 9.0 GeV on 3.1 GeV ~ 200 mm for KEKB: 8.0 GeV on 3.5 GeV The Asymmetric-Energy B Factories (4S) Patricia Burchat, Stanford

  10. The BABAR Detector The Asymmetric-Energy B Factory at the Stanford Linear Accelerator Center Patricia Burchat, Stanford

  11. Silicon Vertex Tracker (SVT) • 5 double-sided layers • Radiation hard (2 MRad) (will replace modules in horizontal plane ~ 2005) • radius = (32 - 140) mm • angular acceptance in lab: 20.1o to 150.2o • 143k channels (0.94 m2) Patricia Burchat, Stanford

  12. Quartz bar Active Detector Surface Particle Cherenkov light Detector of Internally Reflected Cherenkov Light (DIRC) • Measure angle of Cherenkov Cone in quartz • Transmitted by internal reflection • Detected by~10,000 PMTs Patricia Burchat, Stanford

  13. Blind Analysis Techniques BABAR uses “blind” analysis strategies for the extraction of the time-dependent and time-integrated asymmetries in order to minimize possible experimenters bias. In time-dependent asymmetries, we use a technique that hides not only the result of the fit, but also the visual CP asymmetry in the time distribution. The statistical error on the asymmetry is not hidden. Patricia Burchat, Stanford

  14. CP states sorted by B tag flavor B0 B0 or B0 B0 Btag= B0 Btag= B0 B0 B0 or B0 B0 CP violation dN exp(–|Dt|/tB) ( 1 ± sin2b sin(DmDt) ) Dt distributions with NO experimental effects Flavor states sorted by mixing status B Mixing dN exp(–|Dt|/tB) ( 1 ± cos(DmDt) ) Patricia Burchat, Stanford

  15. unmixed – mixed ~ (1 – 2w) unmixed + mixed ~ p / Dmd perfect flavor tagging and time resolution realistic mistag and finite time resolution - unmixed - unmixed - mixed - mixed Asymmetry  (1 – 2w) cos(DmdDt) Patricia Burchat, Stanford

  16. B0 Lifetime (ps) 1.548  0.032 1.542  0.016 Ratio of B+ to B0 Lifetime 1.060  0.029 1.083  0.017 B0 Mixing Frequency ( x 1012 s-1) 0.472  0.017 0.489  0.009 PDG2000 10 measurements 12 measurements 18 measurements PDG2002 New measurements: 3 B Factory 2 LEP 2 B Factory 1 LEP 3 B Factory 1 LEP Increase in precision of B lifetimes and mixing frequency Patricia Burchat, Stanford

  17. Prospects for future lifetime and mixing measurements • Systematic uncertainties dominated by Dt resolution function and, for mixing, knowledge of the lifetime. • Measure mixing and lifetime simultaneously • Expect <1% uncertainty on Bd mixing in a few years. • Measure DG. • Test assumptions of CP/T/CPT symmetries.   see BD*l n measurement (hep-ex/0207071, ICHEP2002) Patricia Burchat, Stanford

  18. Simultaneous measurement of B0 lifetime and mixing with B0D*ln • Simultaneous fit to 12 signal and background samples - float m, B0, mistag probabilities, signal and background t resolution parameters, fraction of charged B. Floating parameters: Innermost ellipse m, B0 m, B0, mistag m, B0, fB+ m, B0, fB+,mistag All signal t res par Default fit Outermost ellipse error ellipse Chih-hsiang Cheng David Kirkby Tim Meyer Patricia Burchat, Stanford

  19. hep-ex/0207071 (ICHEP) Dmd=0.492±0.018±0.013ps-1 +0.024-0.023 B0 =1.523±0.022ps correlation coefficient (m, B0) = -0.22 Patricia Burchat, Stanford

  20. A little more detail on CP asymmetries… dN exp(–|Dt|/tB) ( 1 ± sin2b sin(DmDt) ) interference between 2 direct decays, such as P and T interference between mixing and decay More generally, dN exp(–|Dt|/tB) ( 1 ± S sin(DmDt) - C cos(DmDt) ) where S = , C = , l = + 2 Im l 1 + |l|2 1 - |l|2 1 + |l|2 q A p A mixing decay Patricia Burchat, Stanford

  21. sin2b Vtb*Vtd b Vcb*Vcd Patricia Burchat, Stanford

  22. Charmonium modes used for measuring sin2b b c , c, c One dominant decay amplitude  theoretically clean! c B0 s KS,L d d Both BABAR and Belle use six charmonium modes: • B  J/ Ks0, Ks0p+p-, p0p0 • B  J/ KL0 • B (2S) Ks0 • B c1 Ks0 • B  J/ K*0, K*0  Ks0 • B c Ks0 Patricia Burchat, Stanford

  23. sin2b data samples in BABAR Bflav Mixing sample ccKs modes B0D(*)-p+/ r+/ a1+ Ntagged=23618 Purity=84% • Data • Data Signal J/y KL J/y Bkg Fake J/y Bkg (MeV) Patricia Burchat, Stanford

  24. hep-ex/ 0207042 (PRL) Ks modes KL modes BABAR 81 fb-1 (88 M BB) 2641 tagged events with Dt measured (78% purity; 66% tagging e) sin2b = 0.741  0.067  0.034 || = 0.948  0.051  0.030 effective tagging eff: e=(28.1  0.7)% Patricia Burchat, Stanford

  25. Golden modes with a lepton tag The best of the best! Ntagged = 220 Purity = 98% Mistag fraction 3.3% sDt 20% better than other tag categories background sin2b = 0.79  0.11 Patricia Burchat, Stanford

  26. sin2b measurement history • “Osaka 2000” measurement • (hep-ex/0008048) • Only J/y Ks and y(2s) Ks. • 1st Paper (PRL 86 2515, 2001) • Added J/y KL. • Simultaneous sin2b and mixing fit. • 2nd Paper (PRL 87 201803, 2001) • Added J/y K*0 and c Ks. • Better vertex reconstruction. • Better SVT alignment and higher Ks efficiency for new data. • Winter 2002 (hep-ex/0203007) • Improved event selection. • Reprocessed 1st 20 fb-1. • e) Current measurement (hep- ex/0207042, PRL) • Improved flavor tagging. • One more CP mode: hcKs. (compiled by Owen Long) d e c b a Patricia Burchat, Stanford

  27. Decrease in Statistical Uncertainty • Curves represent 1/Ldt. • Improvements in statistical uncertainty due to • adding new B decay modes, • improved vertex reconstruction, • improved SVT alignment, • improved tagging performance. Patricia Burchat, Stanford

  28. hep-ex/0208025, sub to PRD RC Belle 78 fb-1 (85 M BB) 2958 events (81% purity) effective tagging efficiency: e=(28.8  0.6)% sin2b = 0.719  0.074  0.035|| = 0.950  0.049  0.025 Patricia Burchat, Stanford

  29. Constraints on upper vertex of Unitarity Triangle from all measurements EXCEPT sin2b b Regions of >5% CL A. Höcker, H. Lacker, S. Laplace, F. Le Diberder, Eur. Phys. Jour. C21 (2001) 225, [hep-ph/0104062] Patricia Burchat, Stanford

  30. World Average sin2b = 0.734  0.055 The Standard Model (and the CKM paradigm, in particular) wins again … at least at the current level of experimental precision, in this decay mode. Patricia Burchat, Stanford

  31. s b t s  s  s b t s B0 B0 s K0 K0 d d d d Other studies of sin2 B0Ks • Pure penguin! • time-dependent asymmetry in B0Ks measures sin2b. • direct charge asymmetry in B+K+ sensitive to new physics. Patricia Burchat, Stanford

  32. B0Ks samples 51 signal events hep-ex/0207070 (ICHEP2002) +0.52 - 0.50 sin2b = -0.19  0.90 • c.f. world average: sin2b = 0.73 ± 0.06 • >2 s difference. • (over) stimulating theoretical interest. Patricia Burchat, Stanford

  33. hep-ex/0207033, PLB B0 ’ KS Belle (45M B pairs) • Penguin mediated. • Sensitive to new physics. +0.07 -0.08 sin2b = 0.28  0.55 Many other studies of B (’)K (*) are being aggressively pursued. Challenge to theoretical models to explain relative rates. * Patricia Burchat, Stanford

  34. B0 B0 88M BB Measurement of “sin2b” in bccd decays: D*D*+ and D*D+ c b t d D(*)- D(*)- c d b c c D(*)+ D(*)+ d d d d • Weak phase for tree decay is same as for bccs but watch out for penguins! • D*D* is vector-vector decay (L=0,1,2) so mix of CP=+1 and –1. D*D* signal yield = 126±13 evts D*D* Im(l) = 0.31 0.43  0.13 |l | = 0.98  0.25  0.09 • If penguins are negligible, Im(l)=-sin2b and |l |=1. • 2.7 s change in lnL.   hep-ex/0207072 (ICHEP2002) CP asymmetries in D* D+ have also been studied in BABAR. Patricia Burchat, Stanford

  35. (bccd) mode B0J/yp0 Nfit= 40±7 hf = + 1 Tree: ~ O(l3) same weak phase as bccs ~49 eventsA = -0.25  0.35  0.06-S = 0.93  0.49 0.08 Penguin: ~ O(l3) adds additional weak phase Patricia Burchat, Stanford

  36. “sin2a” Vtb*Vtd Vub*Vud a Patricia Burchat, Stanford

  37. B0 B0 CP Violation in B0 p+p- u b t d p- p- u d b u u p+ d d p+ d d |P/T| and relative strong phase d are unknown but can, in principle, be determined from an isospin analysis that requires measuring BF for B0p+p-, B0p+p-, B±p±p0, B0p0p0, and B0p0p0. Patricia Burchat, Stanford

  38. A2 A2 A0 Isospin Analysis • The 3 B0, B+pp amplitudes proceed via 2 isospin amplitudes: A0,A2 • CP-conjugated decays B0, B- proceed via A0, A2 • Measurements of 5 time-averaged rates fix lengths of each side but not relative orientation, which comes from time-dep analysis. A(B0p0p0) A2 A0 A(B+p+p0) 2aeff from time-dependent p+p- analysis A2 A(B0p+p-)/2 A(B0p+p-)/2 A2 2a A(B0p0p0) A2 A(B-p-p0) A(B+p+p0) is pure tree.   Gronau and London (1990) (slide from David Kirkby) Patricia Burchat, Stanford

  39. Expectations/Prejudices… • Measure coefficients for both sinDmDt and cosDmDt terms (Spp and Cpp ). • Spp and Cpp are determined by a, b, |P/T|, and d. Assume   Gronau and Rosner, PRD65, 093012 (2002) Patricia Burchat, Stanford

  40. mes and DE for B0 p + p - Kp Patricia Burchat, Stanford

  41. ~44M BB pairs ~88M BB pairs BABAR B0 tags qq and Kp background B0 tags B0 tags hep-ex/0207055 (ICHEP/PRL) Sππ= 0.02 ± 0.34 ± 0.05Cππ= -0.30 ± 0.25 ± 0.04 Belle B0 tags bkgdsubtracted hep-ex/0204002, PRL +0.38 +0.16 -0.27 -0.13 Sππ= -1.21Cππ= -Aππ=-0.94 ± 0.09 +0.25 -0.31 Patricia Burchat, Stanford

  42. Belle Interpretation BABAR Patricia Burchat, Stanford

  43. B0 p  p  88M B pairs +10 -9 N( p  p ) =23 events 2.5 s significance hep-ex/ 0207063 (ICHEP2002) B(p  p ) = < 3.6 x 10-6 B(p  p ) < 0.61  B(p  p ) |aeff - a|< 51° @ 90% CL rp   Grossman, Quinn hep-ex/ 0207090 (sub to PRD) cut on likelihood ratio with 20% signal efficiency B(p  p ) = < 6.4 x 10-6 Patricia Burchat, Stanford

  44. hep-ex/0207068 (ICHEP2002) Arπ= -0.22 ± 0.08 ± 0.07AKπ= +0.19 ± 0.14 ± 0.11 B0 “rp ” Clear B0signal observed in rp region of p+p-p0 Dalitz plot. From counting # of “rh+” and “rh-” events… Patricia Burchat, Stanford

  45. hep-ex/0207068 (ICHEP2002) Srπ= +0.16 ± 0.25 ± 0.07Crπ= +0.45 ± 0.19 ± 0.09 From time-dependence of “rp” events… continuum background B background Interpretation in terms of angles of unitarity triangle difficult! Patricia Burchat, Stanford

  46. sin2 Vub*Vud g Vcb*Vcd Patricia Burchat, Stanford

  47. Charmless Two-Body Decays In decays such as B  K p, interference between the Tree and Penguin amplitudes can lead to CP asymmetries that depend on g AND the strong phase difference. Also, ratios of BF for various p p and K p decay modes are sensitive to the angle g. Goal: Measure CP asymmetries AND branching fractions for all charmless two-body final states. Patricia Burchat, Stanford

  48. Charmless 2-Body B Decays Preliminary ~88MB pairs ~60MB pairs Patricia Burchat, Stanford

  49. CP asymmetries in charmless modes New ACP sensitivity for BK+p- = ± 0.05 red  dominant penguin blue  dominant tree • Details in hep-ex/0207065, 0206053, 0207055, • 0207087, PRL88 101805, PRD65 091101, PRD65 051101 Patricia Burchat, Stanford

  50. Charmless Three-Body B Decays: why are they interesting? Sensitive to same weak phases as charmless 2-body decays. Dalitz plot analyses of 3-body decays can (eventually) be used to help disentangle relative strong phases. Already being done in charm decays. A long way to go in B physics, but we’re starting… Patricia Burchat, Stanford

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