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Part III CP Violation and K Physics

Part III CP Violation and K Physics . C hris P arkes. Outline. PHENOMENOLOGY AND EXPERIMENTS CP violation and Kaon physics T-violation: CPLEAR An angle (phase difference) measurement: CPLEAR ε ’ : NA48 Rare kaon decays CP violation and B physics CP Violation and D physics

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Part III CP Violation and K Physics

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  1. Part III CP Violation and K Physics Chris Parkes

  2. Outline • PHENOMENOLOGY AND EXPERIMENTS • CP violation and Kaon physics • T-violation: CPLEAR • An angle (phase difference) measurement: CPLEAR • ε’ : NA48 • Rare kaon decays • CP violation and B physics • CP Violation and D physics • Concluding remarks • Present status and future ahead

  3. Mixing in the neutral kaon system

  4. Neutral kaon system K0 – K0 in nature (1/2) flavour eigenstates, CP conjugated • If CP was conserved: • In nature, CP violated: with • quantifies degree of CP violation

  5. Neutral kaon system K0 – K0 in nature (2/2) Neutral kaons “identity card”: • Branching fractions: • KS :p+p- 69% , p0p0 31% • KL :p0p0p0 21% , p+p-p0 13% , pn 66% • Mixing parameters: ~600 times larger! KSoo KS+- KL+-o KLooo CP=+1 CP=-1

  6. Neutral kaon mixing - oscillations • Feynman (box) diagrams for neutral kaon mixing: d s - W- K0 K0 u, c, t u, c, t _ _ W+ d s s d - u, c, t K0 _ W+ W- _ _ K0 _ _ u, c, t d s At t>0: superposition of states t=0: initial K0 beam Pure KL beam after a while! KS decay early

  7. CPLEAR T-invariance (can also think of it in terms of CP violation) Rate differenceKoKo  KoKois T violation

  8. Experiment at LEAR ring at CERN 1990-1996 Pions from kaon decay

  9. CPLEAR Final states f, f are particle /anti-particles measure 1) Identify Ko / Ko at production: produced in association with K+/K- 2) Identify Ko / Ko at decay from charge of lepton: Get positron: Or electron: ν ν e+ e- W+ W- s u s u Ko π- Ko π+ d d d d

  10. Oscillation t=0 t K0 K0 K0 K0 K0 K0

  11. Oscillation & Decay t=0 t K0 K0 K0 K0 ν ν K0 e+ e- W+ W- s u s u Ko π- Ko π+ K0 d d d d

  12. CPLEAR T-Invariance T or equivalently CP is violated by this tiny amount

  13. CPLEAR : decay to CP eigenstate • Illustrate 3 types of CP violation • Measuring an angle (phase difference)

  14. CPLEAR – decay to π+π- measure Same final state f in both cases 1) Identify Ko / Ko at production: produced in association with K+/K- 2) Decay to π+π- final state reachable from Koand Ko Interference of route with/without oscillations

  15. Oscillation t=0 t K0 K0 K0 K0 K0 K0

  16. Oscillation & Decay t=0 t K0 Amplitude K0 K0 Rate K0 Amplitude K0 K0 Rate

  17. Three methods of CP Violation Revisited Rates CP violation in decay CP violation in mixing CP violation in interference mixing/decay

  18. (since ) Hence we are measuring an angle ϕ+- c.f. B system discussion later

  19. NA48: Direct CP Violation

  20. The e and e’ parameters (1/2) • CP violation first seen though existence of decay modes • CP conservation would imply …. but experimentally these parameters are found ~ 10-3 • CP violation due solely to mixing would be independent of the decay to the final state

  21. The e and e’ parameters (2/2) • To separate CP violation in decay from CP violation in mixing, the following is introduced: … to separate the channel-independent term e from the channel-dependent term e’ • Measurement of rates yields CP violation in mixing Direct CP violation (i.e. in decay) KL/Ks rates:

  22. The NA48 experiment at CERN (1/2) Study of direct CP violation in the neutral kaon system

  23. Start with a pure Kobeam After a few meters (short time) all Ks component decayed Introduce slab of material in beam Several reactions can occur with the material: elastic scattering charge exchange Hyperon production K0absorbed more strongly! f amount of K0 absorbed, f amount of K0 absorbed Neutral kaon regeneration Ks regenerated! A consequence of particle-antiparticle mixing

  24. Measurements of e’/e: Discovery of Direct CP violation Direct CP Violation Average: 1.68 ± 0.14  10-3 Not easy to compare with SM theory - CP violation frontier now in B and D

  25. Rare kaon decays

  26. Rare Kaon Decays Look for extremely suppressed decays in SM – where new physics could contribute Precision currently at parts per trillion ! Some interesting modes New Physics Example Same experimental signature Standard Model Very light/massless neutralino – neutral SUSY particle

  27. Mainly (and very) sensitive to Vtd • Predicted B. R. ~ 8x10-11 One such event Enhancement over SM of central value, but not significant

  28. Also Koto expt, Japan Rare kaon decays – NA62 (successor to NA48) NA62 at CERN’s SPS currently commissioning, to measure Start after CERN (LHC) accelerator shutdown ~11 MHz of K+ decays p+ K+ n n Expect

  29. Key Points – Kaon section • Ks (short lived) , KL (longlived) are mixture of K1 (CP +ve), K2 (CP –ve) • ε quantifies degree of CP violation • CPLEAR measurement of T (or equiv. CP) Violation • KoKo  KoKo • CPLEARCP violation in a CP eigenstate π+π- • same final state f, defined Parameter η+- • How to measure an angle • NA48Direct CP Violation • Difference in CP violation in π+π-,π0π0 • Quantified by e’/e • Rare Decays, extremely suppressed in SM, new physics can contribute • NA62

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