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Cracking the CKM Triangle – B A B AR ’s Next Step –

Cracking the CKM Triangle – B A B AR ’s Next Step –. Masahiro Morii Harvard University B A B AR Collaboration October 2003. Outline. Very brief introduction CKM triangle and CP violation in the B system B A B AR and PEP-II What we can do today, and in 3 years Measurements

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Cracking the CKM Triangle – B A B AR ’s Next Step –

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  1. Cracking the CKM Triangle – BABAR’s Next Step – Masahiro Morii Harvard University BABAR Collaboration October 2003

  2. Outline • Very brief introduction • CKM triangle and CP violation in the B system • BABAR and PEP-II • What we can do today, and in 3 years • Measurements • Angle b from B  yKS/L , fKS , h’KS • Angle a from B  pp • Angle g from B  Dp, DK • |Vub| from B  Xuln decays • Summary Masahiro Morii

  3. Wolfensteinparameters CKM Matrix • CKM matrix appears in the weak Lagrangian as • Unitary matrix translates mass and weak basis • 3 real parameters + 1 complex phase • CPV in the Standard Model is uniquely predictive • Attractive place to look for New Physics The only source of CPV in the Minimal SM Masahiro Morii

  4. Why CP Violation? • Standard Model is unreasonably successful • It predicts everything we measure, while • We all know it’s wrong • BIG failing: Baryogenesis • Matter-dominant universe is created through: • CP violation • Baryon number violation • Non thermal equilibrium • SM prediction falls way short of reality • CKM mechanism was a postdiction of CPV • Never tested (before BABAR) its predictive power All three availablein the Standard Model Masahiro Morii

  5. Unitarity Triangle • V is unitary  Consider • Dividing by gives the familiar triangle • Non-zero angles  CP violation • All sides are O(1)  Can test closure with realistic experimental precision Masahiro Morii

  6. W+ s/b d W- d s/b Anatomy of B0System • B0-B0 system very similar to K0 system • Mixing through box diagrams • Coupling constants appear as • Mass eigenstates BH and BL are linear combinations • Lifetime GH and GL close  Ignore DG • Follow the time evolution… Mass difference Dmcauses mixing Masahiro Morii

  7. B0 Evolution and Decay • Starting from pure B0(B0) state, after time t • Now, consider decays into a CP eigenstate fCP • It’s trivial (just tedious) to calculate the decay rates Neat problem for anundergrad. QM exam Masahiro Morii

  8. mixing CP Asymmetry hf = CP eigenvalue of fCP Scenario 1: There is only one diagram   For B0J/yKS, -Im(lf)=sin2b • Scenario 2: • More than one diagram contribute • both sin and cos terms will survive • Sfdepends on Iml  UT angles • Cf depends on |l|  direct CP Masahiro Morii

  9. Measuring CP Violation • Experiments must do 3 things: • Produce and detect B  fCP events • Typical BR: 10-4 – 10-5 • Need a lot of lot of lot of lot of B’s • Separate B0 from B0 = “Flavor tagging” • Use U4SB0B0 and tag one B • Measure the decay time • Measure the flight length bgct • But B’s are almost at rest in U4S decays Solution: Asymmetric B Factory Masahiro Morii

  10. e+ Three Ingredients e- Ingredient #2: Flavor tagging Btag B0 e- U(4S) m+ B0 Breco Ingredient #1: Exclusive reconstruction p+ p- m- Dz~bgc Dt Ingredient #3:Dt determination Masahiro Morii

  11. Asymmetric B Factory • Collides e+e- at ECM = m(Y4S) but with E(e+) ≠ E(e-) • PEP-II: 9 GeV e- vs. 3.1 GeV e+ bg = 0.56 • The boost allows measurement of Dt • Collides lots of them: Ibeam = 1 – 3A • PEP-II luminosity 6.6 x 1033/cm2/s = 6.6 Hz/nb • That’s >2x the design  • KEKB has hit 1 x 1034/cm2/s  Masahiro Morii

  12. Integrated Luminosity • >100 fb-1/expt. accumulated • Physics results used 90-130fb-1 so far Masahiro Morii

  13. 600 15 10 400 Integrated luminosity [fb-1] Peak luminosity [1033] 5 200 Luminosity Projection – PEP-II • That’ll give BABARa billion B mesons to play with PEP-II plans todeliver 500 fb-1by end 2006 Masahiro Morii

  14. Luminosity Projection – KEKB KEKB also shoot for 500 fb-1 by end 2006 Masahiro Morii

  15. Detector: BABAR (or Belle) Photon energy with a CsI(Tl) crystal calorimeter Charged particle momentum with a drift chamber in a 1.5T field Muons detected after penetrating iron yoke Particle ID with a Cerenkov detector(DIRC in BABAR,aerogel in Belle) Precise vertex with a silicon strip detector Masahiro Morii

  16. Harvard Group At Work New 3D track trigger system for better backgd. rejectionat higher luminosity “ZPD” Masahiro Morii

  17. b B0 Charmonium + K0 • The “golden mode” • Theoretically clean • Only the tree diagram matters • Experimentally clean • “Large” BF (~10-4) • CP sample in 89 M BB pairs ACP(t) = sin2b sinDmDt Masahiro Morii

  18. b CP=+1 CP=-1 sin2b= 0.741 ± 0.067stat± 0.034syst BABAR 81 fb-1 PRL 89, 201802 (2002) CP Fit  sin2b Masahiro Morii

  19. b Unitarity Triangle • World average: sin2b = 0.736 ± 0.049 • Excellent agreement with SM constraint from indirect (non-CPV) data • Does that mean no New Physics? sin2b vs. indirect constraints Observed CP asymmetry consistent withCKMmechanism being the dominant source ofCPV Masahiro Morii

  20. Next Step • We’ve achieveds(sin2b) < 5% • Already more precise than the indirect constraints • Use it as the reference! • B0 yK0 is a tree decay • New Physics may be hidingin more suppressed diagrams • Strategy: Measure “other aspects” of the CKM triangle • Modes with different Feynman diagrams and • Clean theoretical interpretations  Look for inconsistencies= New Physics Masahiro Morii

  21. Cracking the CKM Triangle • Let’s measure everything we can! sin2a from B  pp decays Vub from charmless semileptonic B decays Bs mixing at Tevatron g from B  Dp and B  DK decays sin2b from penguin decays, e.g. B  fK Masahiro Morii

  22. b sin2b Measurements • “Redundant” measurements using other decay modes • Different diagrams  Different sensitivity to New Physics • Loop diagrams are particularly interesting • Theoretically clean modes are more useful • Single-diagram decays preferred • Modes under study Clean Less clean Masahiro Morii

  23. b B0  f/h’ KS • Dominated by b  sss penguin • ACPSM = sin2b = ACP(J/y KS) • New Physics may enter the loop • fKS is pure-penguin • As clean as J/yKS • Small BR: 7.6 x 10-6 • h’KS has tree diagrams too • Cabbibo- and color-suppressed • |A/Ā| ~ 1 within a few % • Larger BR: 5.5 x 10-5 • h’ decays harder to reconstruct Masahiro Morii

  24. b Penguin Signals Preliminary LP’03 BABARfKS Belle BABARh’KS Masahiro Morii

  25. b Penguin CPV Results Preliminary LP’03 Something very strange is happening here… Masahiro Morii

  26. b B0 f KS CP Fits Preliminary LP’03 BABAR Belle Low-purity tags High-purity tags B0 tags B0 tags ACP Masahiro Morii

  27. b B0 h’ KS CP Fits Preliminary LP’03 BABAR Belle B0 tags Low-purity tags B0 tags High-purity tags ACP Masahiro Morii

  28. b Status of Penguins • B0fKS • Belle 3.3s from J/yKS • Prob. < 0.1% • BABAR – Belle = 2.1s • Prob. = 3.6% • Average = –0.14 ± 0.33 • 2.6s from J/yKS • B0 h’KS • Average = 0.27 ± 0.21  2.2s from J/yKS • Do we have a hint of New Physics? • Theorists “told you so” for this very decay mode • Too early to tell  4x more data will settle the case Masahiro Morii

  29. Cracking the CKM Triangle a from B  pp decays |Vub| from charmless semileptonic B decays  g from B  Dp and B  DK decays sin2b from penguin decays, e.g. B  fK Masahiro Morii

  30. a Measuring Angle a • Tree diagram of B0 p+p- should give us sin2a • But there are penguin diagrams T = Tree P = Penguin Masahiro Morii

  31. a Taming Penguins • To estimate aeff – a, we need: • P/T ratio – about 0.3 from G(B  Kp)/G(B pp) • d = strong phase difference between P and T • Gronau & London (1990) suggested using isospin relations Measure BF for all modes and combine  Extract aeff – a from data T P C Masahiro Morii

  32. a assumed Allowed Isospin Analysis • Isospin analysis requires BF(B0 p0p0) separately for B0 and B0 • Too hard for BABAR/Belle  Only average measured • UseBF(B0 p0p0) to put upper bound on aeff – a • Grossman and Quinn, 1998; Charles, 1998 Gronau, London, Sinha, SinhaPLB 514:315-320, 2001 Masahiro Morii

  33. a Observation of B0 p0p0 • BABAR has observed B0 p0p0at 4.2s significance • Weak limit on aeff – a hep-ex/0308012 2(aeff – a) Allowed Masahiro Morii

  34. a CPV in B0 p+p- • B-Physics News of 2002:Belle “discovery” of large CPVin B0 p+p- • PRD 68 (2003) 012001 • CPV ≠ 0 at >99.9% CL • Not seen by BABAR 2.6s discrepancy • Did more data help? BABAR Belle Masahiro Morii

  35. a New world average: Spp = -0.58±0.20 Cpp = -0.38±0.16 Preliminary LP’03 BABAR 123x106 BB Brief History BABAR 33×106BB BABAR 60×106BB BABAR 88×106BB Belle 85×106BB Belle 45×106BB Masahiro Morii

  36. a CP Asymmetries BABAR preliminary Belle PRD 68 (2003) 012001 B0 tags B0 tags B0 tags B0 tags Masahiro Morii

  37. a Status of aeff • BABAR-Belle compatibility improved from 2.6s to 2.0s • Waiting for new result from Belle • Interpretation of aeff a remains murky • BF(B0 p0p0) too large for useful limit on |aeff – a| • Full isospin analysis beyond reach of existing B factories • Several model-dependent analysis proposed Masahiro Morii

  38. a Status of a • Different interpretationswith various assumptions“agree” with the indirectconstraint of a • Theoretical error??? • Experimental efforts areshifting towardB0 rp, rr final states • Interference betweenresonances give extra information for |P/T| and d • Broad r on top of non-resonant ppmakes analyses incredibly complicated indirect Masahiro Morii

  39. Cracking the CKM Triangle  a from B  pp decays |Vub| from charmless semileptonic B decays  g from B  Dp and B  DK decays sin2b from penguin decays, e.g. B  fK Masahiro Morii

  40. Vub Why |Vub| • Measurement of sin2b has become more accurate than the indirect constraint • Width of the indirectellipse is determined by|Vub/Vcb| Better measurement of |Vub| More stringent test of the Unitarity Triangle Masahiro Morii

  41. Vub Measuring |Vub| • Measure the rate of charmless semileptonic decays • Catch: charm background • There are many techniques • Exclusive: • Better S/B • Inclusive: Lepton endpoint spectrum, etc. • Better efficiency That’s not a good sign… Masahiro Morii

  42. Vub Why |Vub| Is Hard Error in extrapolation to full acceptance PDG 2002, p. 706 Poor S/B ratio Inclusive Exclusive S/B better Model-dependent calculation of FF Masahiro Morii

  43. Vub How To Improve |Vub| • Measure inclusive G(B  Xuln) • Exclusive G needs better FF calculation  Lattice QCD • Goal: better S/B ratio + larger kinematical acceptance • Minimize charm background • Reduce extrapolation • Three kinematical variables in the Xuln final state • We need a large sample of clean, isolated, and unbiasedB decays  “B beam” Want to use all of them for optimal efficiency and S/B Masahiro Morii

  44. Vub Tagged-B Events • We have a large sample of U(4S)  BB events with one B fully reconstructed • ~1000 decay channels • Efficiency ~0.2%/B • Look at the other B inthese events (“recoil” B) • Almost-pure B0, B± withknown momentum • Purity known from mES fit • Subtract background using sideband Y± is any combinationof p±, K±, KS and p0 Ideal sample for branching fraction measurements Masahiro Morii

  45. Vub BF(B  Xuln) • Start from the recoil-B sample • Find a lepton with p > 1 GeV • Calculate mass of the remaining system “X” • Know pB, missing (n) mass = 0 • 2-C fit improves s(mX) from 500  350 MeV • Normalization from fitting tag-B mass All events with a lepton Mostly B  Xcln mX > 1.55 GeV Xuln enriched to ~60% Masahiro Morii

  46. Vub BF(B  Xuln)  |Vub| • Fit the mX distribution to extract BR • Use OPE calculation hep-ex/0307062 submitted to PRL OPE mb Masahiro Morii

  47. Vub Theoretical Errors • Signal efficiency depends on (El, q2, mX) distribution • Differential rate predicted at parton level to O(as) • Depends on the b quark mass and its Fermi motion Leading systematics for |Vub| • Parameterized in • Same parameters determine (El, q2, mX) for B  Xcln • Above values come from CLEO’s electron spectrum • We should be able to improve! • Measure both El and mX spectra in B  Xcln • mX requires the recoil-B technique Masahiro Morii

  48. Vub Hadron Mass Moment • Start from recoil-B with lepton • Calculate mX as in the |Vub| analysis • Subtract (small) B  Xuln contribution • Calculate moments <mX> <mX2> <mX3> <mX4> • Vary the lepton p cut from 0.9 to 1.6 GeV BABAR preliminary Coming Soon: Combine with Ee spectrum and fit  determine L and l1 Masahiro Morii

  49. Vub Status of |Vub| • BABAR/Belle/CLEO are working hard on |Vub| • BABAR is leading with the recoil-B technique • Improvements continue • El and mX spectra  Better L and l1 • Cut on q2 Reduced theoretical error • Tag B with semileptonic decays  higher efficiency Masahiro Morii

  50. Cracking the CKM Triangle   a from B  pp decays |Vub| from charmless semileptonic B decays  g from B  Dp and B  DK decays sin2b from penguin decays, e.g. B  fK Masahiro Morii

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