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CP Violation: la B epoque

elle. CP Violation: la B epoque. CP studies using Beauty mesons. Stephen L.Olsen U. of Hawaii. U-Mass Colloquium Mar 12, 2003. CP Violation:. Matter. anti- matter. Asymmetries. Big Bang. all matter no antimatter. matter- antimatter symmetric.

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CP Violation: la B epoque

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  1. elle CP Violation: la B epoque CP studies using Beauty mesons Stephen L.Olsen U. of Hawaii U-Mass Colloquium Mar 12, 2003

  2. CP Violation: Matter anti- matter Asymmetries Big Bang all matter no antimatter matter- antimatter symmetric

  3. Standard Model Symmetries Weak Strong& EM yes violated (maximally) yes violated (small??) violated (pretty badly) yes violated (~20% level) yes

  4. WI: the SM’s industrial sector matter-antimatter differences CP violation Flavor mixing Flavor violations flavor violations gauge symm violations Masses

  5. Today’s talk level CP violation Flavor-mixing Phys 100 B(eauty) mesons B-meson primer (why are they interesting?) CP-violation measurements harder What’s next?

  6. Antimatter & CP (a la Physics 100)

  7. p = mV x px = mVx 2 2 ( ) E = mc2 E = ± mc2 if px is negative  motion is backwards in x if E is negative  motion is backwards in time!!!

  8. backward time motion B - - - - t - - - - when viewed forward in time: - : C - + : P L R

  9. antimatter CP: matter “charge” CP operator: CP( )= g q q g* q q J J† mirror if g g* (i.e. charge is complex): CP symmetry is violated (matter & antimatter behave differently)

  10. CP violation discovered in 1963 seen as a tiny (~0.002) effect in certain K0 decays (not in p or nuclear b-decays) • need a complex coupling specific to strangeness-changing processes

  11. Flavor-mixing

  12. Strangeness-changing weak decays circa 1963 eg: Kp e-n Lp e-n (Flavor-mixing in the 3-quark era) u d s

  13. 3 quarks: q=+2/3 s Weak interactions q=-1/3 4 leptons:

  14. Strength of the Weak interaction Problem 1: Different weak interaction “charges” for m, n, and K decays: GF m- Gs Gd s d K- n u u p0 p Gd 0.98GF Gs 0.2GF

  15. Cabibbo sol’n:flavors mix Weak Int flavor state Flavor mass eigenstates d = ad + bs bGF aGF u GF u u = + s d’ d W- W- W- Unitarity: |a|2 + |b|2 = 1 Cabibbo angle a=cosqc; b = sinqc

  16. Missing neutral currents Problem 2: no flavor-changing “neutral currents” seen. s GN OK K- d d,u d,u p- flavor-changing neutral currents (e.g. Kpl+l-) are strongly supressed flavor-preserving neutral currents (e.g. nNnX) are allowed

  17. GIM sol’n:Introduce 4th quark 2 quark doublets: charmed quark 4-quark flavor-mixing matrix Mass eigenstates Weak eigenstates Unitarity: g = a , d = -b* & |a|2 + |b|2 = 1

  18. GIM cancellation of FCNC Charged currents u(c) bGF aGF u(c) s(d) d(s) W- W- forced to 0 by Unitarity =1 0 Neutral currents (a2+b 2)GN (ab+gd)GN d(s) d,(etc) d,(etc) s(d) Z0 Z0 Flavor preserving Flavor changing OK

  19. Incorporating CPV via flavor mixing

  20. a complex flavor-mixing matrix? a b -b* a Why not incorporate CPV by making  complex? not so simple: a 2x2 matrix has 8 parameters unitarity: 4 conditions 4 quark fields: 3 free phases # of irreducible parameters: 1 Cabibbo angle

  21. 2-generation flavor-mixing cosqCsinqC -sinqC cosqC a b -b a  Only 1 free parameter: the Cabibbo angle not enough degrees of freedom to incorporate a complex number qC120

  22. Enter Kobayashi Maskawa suppose there are 3 quark generations: a 3x3 matrix has 18 parameters unitarity: 9 conditions 6 quark fields: 5 free phases # of irreducible parameters: 4 one complex phase is possible! three are needed for 3-dim rotation (e.g. Euler angles)

  23. KM (+others) circa 1973 (Kyoto) Makoto Kobayashi Toshihide Maskawa

  24. Original KM paper From: Prog. of Theor. Phys. Vol. 49 Feb. 2, 1973 3 Euler angles CP-violating phase

  25. A little history • 1963 CP violation seen in K0 system • 1973 KM 6-quark model proposed • 1974 charm (4th ) quark discovered • 1978 beauty/bottom (5th) quark discovered • 1984 KM model makes it into PDG book • 1995 truth/top (6th) quark discovered • 2001 CPV in B-meson decays discovered

  26. CKM matrix (in 2002) CPV phases are in the corners * Vub f3 (g) u b W+ f1 (b) d t W+

  27. Unitarity † * * * + VcdVcb + VtdVtb = 0 VudVub * Vtd Vtb * Vud Vub 2 phase of Vtd 1 3 phase of Vub * Vcd Vcb

  28. Testing the KM CPV mechanism 1st step: show that at least one fi  0 QM: phase measurement requires interference

  29. Primer on B mesons

  30. Lesson 1: Basic properties • What are B mesons? • B0 = d b B0 = b d • B+ = u b B- = b u • JPC = 0- + • t= 1.5 x 10-12 s (ct  450 mm) • How do they decay? • usually to charm: |bc|2  |bu|2 100 • How are they produced? • e+e-  (4S)  B B is the cleanest process

  31. Lesson 2: “flavor-tagged” B decays In ~99% of B0 decays: B0 and B0 are distinguishable by their decay products semileptonic decays: X l+ n X l- n B0 B0 hadronic decays: D X D X B0 B0

  32. Lesson 3: B  CP eigenstate decays In ~1% of B0 decays: final state is equally accessible from B0 and B0 charmonium decays: J/yKS J/yKL … B0 B0 charmless decays: p+p- K+K- … B0 B0

  33. Lesson 4:The (4S) resonance 3S bb bound states • (e+e- BB)  1nb • B0B0/B+B- 50/50 • good S/N • BB and nothing else • EB = Ecm/2 • coherent P-wave • B’s  at rest in CM s(e+e-) hadrons BB threshold

  34. Lesson 5:Recurring question: What makes the b-quark interesting? • CESR/CLEO • PEPII/BaBar • KEKB/Belle • ~50% of CDF & D0 • BTeV • LHCB • …..

  35. Lesson 5: Consider 2nd order bd(s) FCNC bd: * * * Vub Vud Vcb Vcd Vtb Vtd + + b u d b c d b t d * * * A=VubVud f(mu) + VcbVcd f(mc) + VtbVtd f(mt) * * * GIM: VubVud+VcbVcd+VtbVtd = 0 same for bs a big if  A = 0if mu = mc = mt

  36. Lesson 6:Large mt overides GIM but, mt >> mc & mu: GIM cancellation is ineffective V* td V* td B0 B0 mixing transition is strong (and this accesses Vtd)

  37. Lesson 7:loops are accessible also, because mt >> mc & mu: GIM-forbidden “penguins” are accessible effects of massive virtual particles can show up here

  38. B-meson primer: final exam Q. What makes B’s interesting? A. The large t-quark mass: mt=174 GeV

  39. Measuring KM phases

  40. Sanda, Bigi & Carter Technique Proposed in 1981, before large t-quark mass & BB mixing was discovered • Use B  CP eigenstate decays (fCP) • eg BJ/ KS & BJ/ KS • Interfere BfCP with BBfCP Br(BfCP) are small (<10-3) need millions of B mesons

  41. Interfere BfCPwith BBfCP Sanda, Bigi & Carter: J/y Vcb B0 KS  + V*2 td J/y sin2f1 V* Vtb Vcb td B0 B0 B0 KS V* Vtb td td

  42. What do we measure? Flavor-tag decay (B0 or B0 ?) Asymmetric energies J/ e fCP e t=0 KS z B - B B + B sin21 more B tags t z/cβγ (tags) more B tags This is for CP=-1; for CP=+1, the asymmetry is opposite

  43. What’s needed? • Lots of B mesons (Br (BfCP) ~ 103) • very high Luminosity KEKB • Find CP eigenstate decays • high quality ~ detector  Belle • “Tag” the other B’s flavor • good particle id  dE/dx, Aerogel, TOF • Measure decay-time difference • Asymmetric energies  (@KEKB:g b ct200mm) • good vertexing  silicon strip vertex detector • Extract results

  44. Step 1:make B mesons KEKB

  45. KEKB • Two separate rings • e+ (LER) : 3.5 GeV • e- (HER) : 8.0 GeV • ECM : 10.58 GeV at (4S) • Luminosity • target: 20 B’s /sec • achieved: ~15B’s/sec • ±11 mrad crossing angle • Small beam sizes: • sy3 mm; sx  100 mm asymmetric e+e-collider

  46. world records 15 B’s/sec 800K B’s/day ~140M B’s

  47. TheBelleCollaboration A World-Wide Activity Involving ~50 Institutions

  48. la elle A magnetic spectrometer based on a huge superconducting solenoid

  49. The Belle Collaboration ~250 Authors

  50. Step 2: Select events J/ KS B0 J/ Ksevent

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