: Chris Parkes Part V CP violation and D Physics

Chris Parkes2 Outline PHENOMENOLOGY AND EXPERIMENTS III.CP violation and Kaon physics Mixing in the neutral kaon system Neutral kaon decays Rare kaon decays IV.CP violation and B physics B factories, old and future experiments Mixing in neutral B mesons Benchmark B decays Rare B decays V.CP Violation and D physics Mixing in neutral D mesons Direct and Indirect CP Violation Searches Future prospects VI.Concluding remarks

D mesons c 

Chris Parkes4 Mixing :  D 0 mixing slightly different from K 0 and B 0 (s) mixing  only ‘up’ type quark system that can mix  D 0 mixing 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….) Why study mixing and CP violation in the D sector?

Mixing in neutral D mesons BaBar and Belle find first evidence for D 0 mixing Well established by combining multiple channels Announcement at the Rencontres de Moriond Conference in March 2007 BaBar and Belle find first evidence for D 0 mixing Well established by combining multiple channels Announcement at the Rencontres de Moriond Conference in March 2007 First single channel 5σ measurment D 0 mixing LHCb, November 2012 First single channel 5σ measurment D 0 mixing LHCb, November 2012

Chris Parkes6 Mixing in the neutral D 0 – D 0 system c u d, s, b WW WW _ u c _ c u WW WW _ u c _ _ _ _ D0D0 D0D0   Feynman (box) diagrams for D 0 mixing: down type quarks in loops D0D0 D0D0  _ _ _  b loop CKM suppressed from Wolfenstein parametrisation is order (λ 3 λ 2 ) 2  and s,d loops GIM suppressed  Long distance effects important – but difficult to calculate

Chris Parkes7 reminder x<<1 Only small fraction of an oscillation before decay suppressed

Chris Parkes8 1. Flavour at production Key points on D mixing Hence, don’t need to use the flavour tagging procedures we discussed for B, mistag rate will be low 2. Decay Diagrams Right sign – Cabibbo Favoured Wrong sign – Double Cabibbo Suppressed

Chris Parkes9 1. Wrong sign / right sign Key points on D mixing 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

Chris Parkes10

Chris Parkes11 1. Wrong sign / right sign Key points on D mixing Flat with time? no mixing, increases with time ? mixing See just first part of oscillation curve

Indirect CPV

Chris Parkes13 A Γ : indirect CP violation * * Actually it has a direct CP violation contribution if direct CPV is large, see arXiv: v2 (our group) 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

Oscillation & Decay 14 t=0t D0D0 D0D0 D0D0 D0D0 D0D0 D0D0 CP Violation A m A d Weak Phase ϕ

Prompt/Secondary Separation 15 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…. ArXiv: (2013) (our group)

Direct CPV

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

Production Asymmetry of D *+ Technical Scale Drawing of LHC Collision Chris Parkes 18 Proton (Matter) Cancel by measuring difference of KK and ππ final states +ve charge -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, (2012)

World Average Results World Average Results 19 ΔA CP : direct CP violation A Γ : indirect CP violation (some tension more results needed )

Chris Parkes20 Mixing Fully established - 5 σ 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 taken in last year !  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 Status / Future prospects (and a number of good LHCb PhD thesis topics…)

Chris Parkes21 Key Points – D section Neutral meson mixing only ‘up’ type system x<<1, very slow oscillations Long distance effects important, not only box diagrams D 0 -> 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