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Chris Parkes

:. Part V CP violation and D Physics. Chris Parkes. Outline. PHENOMENOLOGY AND EXPERIMENTS CP violation and Kaon physics Mixing in the neutral kaon system Neutral kaon decays Rare kaon decays CP violation and B physics B factories, old and future experiments

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Chris Parkes

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  1. : Part V CP violation and D Physics Chris Parkes

  2. Outline • PHENOMENOLOGY AND EXPERIMENTS • CP violation and Kaon physics • Mixing in the neutral kaon system • Neutral kaon decays • Rare kaon decays • CP violation and B physics • B factories, old and future experiments • Mixing in neutral B mesons • Benchmark B decays • Rare B decays • CP Violation and D physics • Mixing in neutral D mesons • Direct and Indirect CP Violation Searches • Future prospects • Concluding remarks

  3. D mesons c  Nucl.Phys. B871 (2013) 1-20

  4. Why study mixing and CP violation in the D sector? • Mixing: • D0 mixing slightly different from K0 and B0(s)mixing • only ‘up’ type quark system that can mix • D0mixing only recently observed experimentally (2007 onwards) • Beyond Standard Model (BSM) effects may enhance mixing • (Accurate) SM and BSM theoretical calculations/predictions are difficult and show a broad range of estimates • why?: D-mesons are too light to be treated as heavy … and too heavy to be treated as light! • CP violation: • Predicted to be negligible in the SM  large effects would be evidence for New Physics … • Experimental evidence for CP violation with D mesons not yet clear • (CPV in Kaons got a Nobel prize, CPV in B got a Nobel prize…)

  5. Mixing in neutral D mesons BaBarand Belle find first evidence for D0mixing Well established by combining multiple channels Announcement at the Rencontres de Moriond Conference in March 2007 First single channel 5σ measurment D0mixing LHCb, November 2012

  6. Mixing in the neutral D0 – D0 system • Feynman (box) diagrams for D0 mixing: down type quarks in loops c u _ _ _ - W+ D0 D0 d, s, b d, s, b _ _ W- c u u c d, s, b - _ _ D0 _ W+ W- D0 _ _ d, s, b u c • b loop CKM suppressed from Wolfensteinparametrisation is order (λ3λ2)2 • and s,d loops GIM suppressed • Long distance effectsimportant • – but even more difficult to calculate

  7. reminder x<<1 Only small fraction of an oscillation before decay suppressed suppressed suppressed suppressed DCS interference mixing

  8. Key points on D mixing 1. Flavour at production Hence, don’t need to use the flavour tagging procedures we discussed for B, mistag rate will be low 2. Decay Diagrams Right sign – CabibboFavoured Wrong sign – Double Cabibbo Suppressed

  9. Key points on D mixing 1. Wrong sign / right sign Consider events that are either wrong sign (rare and time independent) or mixed (rare and number will increase with time). to cancel systematics take ratio to right sign events Flat with time? no mixing, increases with time? mixing

  10. Key points on D mixing 1. Wrong sign / right sign Flat with time? no mixing, increases with time ? mixing See just first part of oscillation curve

  11. Another way to measure D mixing yCP Measure lifetime of decays into CP eigenstates → here CP even, e.g. K+K- Assume D2 ≡ p|D0⟩ - q|D̅0⟩ is CP even → then this measures τCP+ = 1 / Г2 Compare to decay into flavour-specific final state, e.g. K-π+ → this measures τ = 2 / (Г1+Г2) ≡ 1 / Г̅ Therefore τ / τCP+ - 1 = Г2 – Г1 / (Г1 + Г2) = ΔГ / (2Г) ≡ y For non-zero CP violation D2 is not the physical state DH→ measure yCP ≡ τ(Kπ) / τ(KK) – 1 = (1 – AM2/8) y cosϕ – AM/2 x sin ϕ Our group Update imminentwith ~100x more data CP Violation Am Weak Phase ϕ

  12. Indirect CPV

  13. AΓ : indirect CP violation * Same concept as B or K measurements we saw before But experimentally different since don’t see oscillations as x is so small Measure from lifetimes of decay to CP eigenstate * Actually it has a direct CP violation contribution if direct CPV is large → see M. Gersabeck, C. Parkes et al., J.Phys. G39 (2012) 045005

  14. Oscillation & Decay t=0 t D0 D0 D0 D0 D0 CP Violation Am Ad Weak Phase ϕ D0

  15. Prompt/Secondary Separation • Experimental Complication • D come from both production in proton-proton (prompt) • And from decay of B to D (secondary) • Separate out to get prompt D for time dependent measurement • Use impact parameter that is the distance of flight vector of reconstructed D from the primary vertex (proton-proton interaction point) • World’s best measurement • No sign of CP Violation yet…. Phys.Rev.Lett. 112 (2014) 041801 (our group)

  16. Direct CPV

  17. ΔACP: Direct CP violation in two-body charm • Search for CP asymmetry • Use decays where slow pion charge determines the D flavour at production Note time-integrated not time dependent What we don’t want (1) What we don’t want (2) What we measure What we want

  18. ΔACP: Direct CP violation in two-body charm Measure difference of raw asymmetries for KK and ππ final states Leads to difference of CP asymmetries (at first order) Araw(KK) - Araw(ππ) ≈ ACP(KK) - ACP(ππ) Expect similar magnitude and opposite sign for ACP(KK) and ACP(ππ) → ACP(KK) - ACP(ππ) ≈ 2 |ACP(KK)| ≈ 2 |ACP(ππ)| Enhanced sensitivity in difference measurement! Chris Parkes

  19. Production Asymmetry of D*+ • Technical Scale Drawing of LHC Collision Proton(Matter) Proton(Matter) +ve charge • Cancel by measuring difference of KK and ππ final states -ve charge Detection Asymmetry of D and of π+s • Symmetric final states • no D detection asymmetry • Difference of final states • cancel slow π+detection asym. • Periodic reversal of magnetic field Phys. Rev. Lett. 108, 111602 (2012) Chris Parkes

  20. World Average Results (some tension more results needed ) ΔACP : direct CP violation AΓ : indirect CP violation

  21. Status / Future prospects • Mixing • Fully established - 5σ single channel measurement • CP violation: • So far there is no clear evidence for CP violation with D mesons – some discrepancy in direct, none in indirect • Large CP Violation would be evidence for New Physics, as SM prediction is small • Prospects: • Enormous samples at LHCb under analysis > 10 billion charm events recorded during LHC run 1! • Picture changing very quickly • In addition to two-body decays discussed here, there is active work on 3-body (and 4-body) final state analyses using Dalitz plots (and a number of good LHCb PhD thesis topics…)

  22. Key Points – D section • Neutral meson mixing • only ‘up’ type system • x<<1, very slow oscillations • Long distance effects important, not only box diagrams • D0 -> K+π-, Wrong sign / right sign event ratio with time • 5σ single channel discovery LHCb • No CP Violation observed (yet) • Small in SM, could be larger due to new physics • Search for indirect CP Violation • Search for direct CP Violation

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