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

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

LHCb was designed for b-quark studies But also ideal for charm 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

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

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 Chris Parkes LHCb-PAPER-2012-026 to be submitted to PLB

LHCb-PAPER-2012-026 to be submitted to PLB 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 Chris Parkes LHCb-PAPER-2012-026 to be submitted to PLB

LHCb-PAPER-2012-026 to be submitted to PLB 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 Chris Parkes LHCb-PAPER-2012-026 to be submitted to PLB

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)

Production Asymmetry of D*+ Technical Scale Drawing of LHC Collision Proton (Matter) Proton (Matter) +ve charge -ve charge Cancel by measuring difference of KK and ππ final states 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 Chris Parkes Phys. Rev. Lett. 108, 111602 (2012)

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 Chris Parkes Phys. Rev. Lett. 108, 111602 (2012)

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 Chris Parkes Phys. Rev. Lett. 108, 111602 (2012)

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)]% Chris Parkes Phys. Rev. Lett. 108, 111602 (2012)

Theorists 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 Phys. Rev. Lett. 108, 111602 (2012) Chris Parkes

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) Chris Parkes JHEP04 (2012) 129

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

Measuring propertime acceptance Chris Parkes JHEP04 (2012) 129

Measuring propertime acceptance Chris Parkes JHEP04 (2012) 129

Measuring propertime acceptance Chris Parkes JHEP04 (2012) 129

Measuring propertime acceptance Chris Parkes JHEP04 (2012) 129

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

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

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 Chris Parkes LHCb-CONF-2012-019

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 Chris Parkes LHCb-CONF-2012-019

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

Summary D± production asymmetry 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

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