1 / 86

Symmetry and Symmetry Violation in Particle Physics

对称. 违反. Symmetry and Symmetry Violation in Particle Physics. Lecture 4 March 28, 2008. Summary Lecture 3. CP is violated in Weak-Interactions Neutral Kaon mass-matrix induced; scale  e  2x10 -3 Direct CPV in K L  pp ; scale = e ’ = 1.6 x 10 -3 e Observing CPV requires:

palila
Télécharger la présentation

Symmetry and Symmetry Violation in Particle Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 对称 违反 Symmetry and Symmetry Violation in Particle Physics Lecture 4 March 28, 2008

  2. Summary Lecture 3 • CP is violated in Weak-Interactions • Neutral Kaon mass-matrix induced; scale  e 2x10-3 • Direct CPV in KLpp; scale = e’ = 1.6 x 10-3e • Observing CPV requires: • Two interfering amplitudes • One with a CP-violating weak phase • Another “common” or “strong” phase • In the W.I., the d and s quark mix  d’ & s’ • d’ =cosqcd +sinqs; s’ =-sinqcd +cosqcs • qc 120 is the “Cabibbo angle • If all quarks are in pairs, FCNC = 0 by Unitarity • (GIM Mechanism)

  3. antimatter CP: matter “charge” CP operator: CP( )= g q q’ g* q W q W† some basic process mirror For CPV:g g* (charge has to be complex)

  4. CP violating asymmetries in QM • Even if CP is violated, generating matter-antimatter differences is hard • need a CP-violating phase (f) • need 2 (or more) interfering amplitudes • + a non-zero “common” phase (d) (often called a “strong” phase)

  5. Common and weak phases “Common” (strong) phase (d): same sign for matter & antimatter  CP conserving Weak phase (f): opposite sign for matter & antimatter  CP violating B = |B|eid-if |B|eid+if f f A+B A+B B B d d A

  6. How does CPV fit into the Standard model? Clue: CPV is seen in strangeness-changing weak decays. It must have something to do with flavor-changing Weak Interactions

  7. CP Violation & Flavor mixing

  8. d’ & s’ are mixed d & s 4-quark flavor-mixing matrix Mass eigenstates Weak eigenstates

  9. how about a complex mixing matrix? b controls |DS|-1 where we see CPV incorporate CPV by making  complex? (i.e. b≠b*?) a b -b* a bGF u s W- not so simple: a 2x2 matrix has 8 parameters unitarity: 4 conditions 4 quark fields: 3 free phases Cabibbo angle # of irreducible parameters: 1

  10. 2-generation flavor-mixing cosqCsinqC -sinqC cosqC a b -b a Only 1 free parameter: the Cabibbo angle s d’ not enough degrees of freedom to incorporate a CPV complex phase s’ qC120 d

  11. Enter Kobayashi Maskawa a 3x3 matrix has 18 parameters unitarity: 9 conditions 6 quark fields: 5 free phases # of irreducible parameters: 4 3 Euler angles +1 complex phase

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

  13. KM paper was in 1973, the 3-quark age 1964-1974 3x3 matrix 3 generations, i.e. 6 quarks Predicted by Glashow but not discovered until Nov.1974 6 quarks: These were not even in our 1973 dreams. 3 quarks: 4 quarks: q=+2/3 s-1/3 q=-1/3

  14. 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 • 1995 truth/top (6th) quark discovered

  15. CKM matrix (in 2008) * Vub u CPV phases are in the corners b f3 (g) W+ d Vtd t W+ f1 (b)

  16. The challenge * Vub u Vtd d b t W+ W+ Measure a complex phase for bu or in td or, even better, both

  17. The Key B0 = d B0 = b b d Use B0 mesons B0/B0 similar to K0/K0

  18. 小学课本 Primer on B mesons

  19. Lesson 1: Basic properties b-1/3 d+1/3 • 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 b+1//3 d-1/3 b-1/3 u-2/3 u+2/3 b+1//3

  20. Lesson 2: “flavor-specific” B decays In >95% of B0 decays: B0 and B0 are distinguishable by their decay products semileptonic decays: X l+ n X l- n B0 B0 D hadronic decays: D X D X q C+2/3 B0 B0 D C+2/3 q

  21. 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 J/y C-2/3 C+2/3 JPC=1-- charmless decays: CP=+ p+p- K+K- … B0 B0

  22. Lesson 4:The (4S) resonance 3S bb bound states BB threshold • (e+e- BB)  1nb • B0B0/B+B- 50/50 • good S/N: (~1/3) • BB and nothing else • coherent 1-- P-wave s(e+e-) hadrons 10.58GeV e+e-qq continuum (u, d, s &c)

  23. _ Lesson 5:B0B0 mixing A B0 can become a B0 (and vice versa) V* b u,c,t td d tb d b u,c,t V* td tb These have a weak phase: f1 (only short-distance terms are important)

  24. bd: * * * Vub Vud Vcb Vcd Vtb Vtd + + b u d b c d b t d * * * Ά=VubVud f(mu) + VcbVcd f(mc) + VtbVtd f(mt) * * * GIM: VubVud+VcbVcd+VtbVtd = 0  Ά = 0if: mu = mc = mt

  25. Large mt overides GIM but, mt >> mc & mu: GIM cancellation is ineffective t-quark dominates V* td V* td B0 B0 mixing transition is strong (and this allows us to accesses Vtd)

  26. Y.H. Zheng, PhD Thesis Also Y.H. Zheng et al., Phys Rev. D 67 092004 (2003) N(B) – N(B) N(B) + N(B)

  27. What makes B’s interesting? The large t-quark mass: mt=174 GeV

  28. Neutral meson mixing phenomenology Neutral B mesons are produced as flavor eigenstates: B0 or B0 B0(t) B0(t) B0(t) B0(t) |B1> = p |B0> + q |B0> |B2> = p |B0> - q |B0> B1 & B2 If CPV is small: q ≈ p ≈1/2

  29. Time dependence of B0 (B0) mesons( pq1/√2 ) |B0(t)> = ( |B0> (1+eiDmt)+ |B0>(1-eiDmt))e-Gt common phase |B0(t)> = (|B0>(1+eiDmt)+ |B0>(1-eiDmt))e-Gt Dm = m2-m1G = (G1 + G2)/2

  30. Can we measure f1? • two processes: B0fcp& B0  B0 fcp • weak phase: 2f1 • common phase: Dmt Yes!!

  31. 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 eiDmt B0 KS V* Vtb td td

  32. 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

  33. Requirements for CPV • Many B mesons • “B-factory” & the ϒ(4S) resonance • Reconstruct+isolate CP eigenstate decays • Kinematic variables for signal +(cont. bkg suppr+PID). • “Tag” flavor of the other B • Measure decay-time difference • Asymmetric beam energies, high precision vertexing(Δz) • Likelihood fit to the t distributions

  34. PEPII B factory in California Stanford Linear Accelerator Ctr BaBar Detector

  35. The PEPII Collider (magnetic separation) Int(L dt)=131 fb-1 On resonance:113 fb-1 9 x 3.0 GeV; L=(6.5 x 1033)/cm2/sec

  36. Superconducting Coil (1.5T) Silicon Vertex Tracker (SVT)[5 layers] e+ (3 GeV) e- (9 GeV) Drift Chamber [40 stereo lyrs](DCH) CsI(Tl) Calorimeter (EMC) [6580 crystals]. Cherenkov Detector (DIRC) [144 quartz bars, 11000 PMTs] Instrumented Flux Return (IFR) [Iron interleaved with RPCs]. The BaBar Detector

  37. KEK laboratory in Japan Tsukuba Mountain KEKB Collider KEK laboratory

  38. KEKB • Two rings • e+ : 3.5 GeV 1.5A • e- : 8.0 GeV 1.1A • ECM : 10.58 GeV • Luminosity: • target: 1034cm-2 s-1 • ach’ved: 1034cm-2 s-1 • (~20 B’s/s)

  39. elle A magnetic spectrometer based on a huge superconducting solenoid

  40. Step 2: Select events p+p- B0 J/ Ksevent m+m- Tracking chamber only

  41. Drift chamber for tracking & momentum measurement

  42. Drift chamber cell Charged particle track E-field - - - - - - - - + 16mm - - Drift speed  50mm/nsec Position resolution  150 mm - - - - 17mm

  43. Same event in the entire Detector J/ KS B0 J/ Ksevent

  44. Kinematic variables for the ϒ(4S) in CM: E=Ecm/2 J/y KS B0 e+ e- e- e+ B0 E=Ecm/2 invariant mass: Beam-constrained mass:

  45. Kinematic variables for the Υ(4S) s10MeV Energy difference: s  2.5 MeV Beam-constrained mass:

  46. B0ψ KL signal event Event display J/ KL 1399±67 signal KL “crash” pB* (cms) [2332 events with a purity of 0.60]

  47. Step 3: Check the other tracks to see if the other meson is a B0 or a B0 ? ? ? ? ? ?

  48. Flavor-tagging the other B Figure of merit(Q) =ε(1-2 w)2a.k.a effective tagging efficiency • Inclusive Leptons: • high-p lb c ln • intermed-p l+s l n • Inclusive Hadrons: • high-p p- B0D(*)+p-, D(*)+r-, etc. • intermed-p K- K- X, p-p0 • low-p p+ D0p+ Belle: effective efficiency = 30 %

  49. Distinguishing different particle types dE/dx Ionization density in the drift chamber (dE/dx)

More Related