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Discovering CP Violation and Mixing in the Charm Sector

Discovering CP Violation and Mixing in the Charm Sector. NEW. D + production asymmetry ΔA CP y CP , A Γ CPV search in four-body pion. On behalf of the LHCb(c?) collaboration. Muon System. Vertex Locator. RICH Detectors. Interaction Point. Tracking System. Calorimeters.

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Discovering CP Violation and Mixing in the Charm Sector

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  1. Discovering CP Violation and Mixing in the Charm Sector NEW D+ production asymmetry ΔACP yCP, AΓ CPV search in four-body pion On behalf of the LHCb(c?) collaboration

  2. Muon System Vertex Locator RICH Detectors Interaction Point Tracking System Calorimeters Chris Parkes

  3. LHCbLHCc c • LHCb was designed for b-quark studies • But also ideal for charm • shorter lived and lower p • 20 times more events Chris Parkes

  4. Charm – Prompt and Secondary • Two types of charm production: • Prompt: charm produced directly in the primary reaction • Secondary: charm produced in B decays [>50% of B->DX] • Prompt charm more abundant • Secondary can have higher purity • Must discriminate between them • Use D impact parameter Chris Parkes

  5. D± production asymmetry • Time-integrated direct CPV searches are sensitive to production effects • Initial pp – no net charm ! • Direct production QCD/EW – cc • But hadronisation with valence quarks can break D+/D- symmetry • Previously measured • Measure: • using NEW LHCb-PAPER-2012-026 to be submitted to PLB Chris Parkes

  6. CPV in decay ? • CPV in D+ ? Cabbibo allowed, tree • Expected 10-4. Measured by Belle • CPV in Ks considered Grossman, Nir arXiv:1110.3790 • Ks decaying inside VELO used • Short lifetime • (mean 7ps, c.f. 90 ps) • Fold with indirect CPV in Ks, ε • Effect is small • 2.8 x 10-4 Preliminary LHCb-PAPER-2012-026 to be submitted to PLB Chris Parkes

  7. Result (prelim.) • Measurement performed in bins (pT,η) Preliminary Preliminary • In kinematic region probed: • 3 σ evidence for a production asymmetry • No significant dependence on pT,η seen at this statistics Primary systematic from trigger asymmetry LHCb-PAPER-2012-026 to be submitted to PLB Chris Parkes

  8. Direct CP violation in two-body charm • Search for CP asymmetry • Use decays where slow pion charge determines the D flavour at production (used in all analyses that follow in this presentation) What we measure What we want What we don’t want (1) What we don’t want (2) Phys. Rev. Lett. 108, 111602 (2012)

  9. 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 π+s detection asym. • Periodic reversal of magnetic field Phys. Rev. Lett. 108, 111602 (2012) Chris Parkes

  10. Subtle Reconstruction Effects Regions of phase space where only a D*+ or D*- can be reconstructed, due to LHCb detector geometry While in principle they cancel in magnet reversal they are removed using fiducial cuts π+s reconstructed π-s not reconstructed Phys. Rev. Lett. 108, 111602 (2012) Chris Parkes

  11. Direct CP Violation in Charm • High Statistics • 1.4M K+K-, 0.4M π+π- • 0.6 fb-1 analysed, • now have 2.5 fb-1 recorded • Many cross-checks have been performed • Independent analysis using secondary charm in preparation Phys. Rev. Lett. 108, 111602 (2012) Chris Parkes

  12. Results • First evidence of CPV in charm decays • Supported by recent CDF and Belle results ΔACP = [-0.62 ± 0.21 (stat) ± 0.10 (syst)]% ΔACP = [-0.87 ± 0.41 (stat) ± 0.06 (syst)]% Phys. Rev. Lett. 108, 111602 (2012) Chris Parkes

  13. Until recently most calculations suggested CPV in charm < 10-3 • There are honourable exceptions e.g. “…There is no theorem, though, ruling out SM effects of 1%” S. Bianco, F. L. Fabbri, D. Benson, and I. Bigi, A Cicerone for the physics of charm, Riv. Nuovo Cim. 26N7 (2003) • 89 citations for LHCb paper • Consensus? • Compatible with NP models, • Large for SM but NOT excluded Theorists Phys. Rev. Lett. 108, 111602 (2012) Chris Parkes

  14. Time-dependent two-body measurements • Lifetime ratio measurements: Pure mixing measurement In absence of CPV • Measured for first time at a hadron collider • 2010 (0.03 fb-1) data only CPV indirect (and direct) JHEP04 (2012) 129 Chris Parkes

  15. Measuring propertime acceptance • Determined from data • “swimming” – move the D vertex and reapply the selection • LHCb trigger – all lifetime biasing selections in software JHEP04 (2012) 129 Chris Parkes

  16. Measuring propertime acceptance JHEP04 (2012) 129 Chris Parkes

  17. Measuring propertime acceptance JHEP04 (2012) 129 Chris Parkes

  18. Measuring propertime acceptance JHEP04 (2012) 129 Chris Parkes

  19. Measuring propertime acceptance JHEP04 (2012) 129 Chris Parkes

  20. Prompt/Secondary Separation • Separate prompt /secondary charm on statistical basis through ln(χ2 IP of D) • Primary systematic, improve with better secondary modelling JHEP04 (2012) 129 Chris Parkes

  21. Results • Based on 2010 data, 0.03 fb-1 JHEP04 (2012) 129 Chris Parkes

  22. Four-body CPV search • Model independent search • Four-body “Dalitz” plot, 5 dimensions • Compare bins across phase space • Sensitive to local variations • SCP normal (μ=0,σ=1) in absence of CPV • α – normalisation – insensitive to global asymmetries • global CP and global detector/production effects • Adaptive binning >100 entries/bin LHCb-CONF-2012-019 Chris Parkes

  23. Detector/production asymmetries • Equal amounts of two magnet polarities • Apply fiducial cuts (as earlier) • Accept/reject in (η,ϕ) space for equal D,D 2011 1fb-1 data, 180k events, 96% purity LHCb-CONF-2012-019 Chris Parkes

  24. CPV Search Results • Method cross-checked • CF decay • Simulated phase differences • No evidence of CPV in • P-value 99.8% LHCb-CONF-2012-019 Chris Parkes

  25. Summary • LHCb’s huge charm samples fulfilling potential • D± production asymmetry • 3σ evidence • ΔACP with CDF+Belle, 4.6σ evidence of CPV • No lose theorem: • New Physics OR the FBI arrest a theorist • yCP and AΓ • First hadron collider measurement – precision results to come • Acceptance effect from data • 3 and 4-body CPV searches • Binned (generalised) Dalitz plot searches NEW (KKπ Phys. Rev. D 84 (2011) 112008) Chris Parkes

  26. 6th International Workshop on Charm Physics Manchester, UK, 31 August – 4 September 2013 Topics: New Charmonium-like Hadrons (XYZ Hadrons) Hidden Charm Spectroscopy and Transitions Production of Charm and Charmonia Hidden and Open Charm in Media Charm Meson and Baryon Spectroscopy Light Hadronic Spectroscopy from Decays of Charm and Charmonia Leptonic, Semileptonic and Rare Charm Decays Advances in Theoretical Tools D -Dbar Mixing and CP Violation New Physics Scenarios for Charm Decays Experimental Charm Facilities - Status and Future

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