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Charm Mixing, CPV and Rare D 0 decays at BaBar

Charm Mixing, CPV and Rare D 0 decays at BaBar. William S. Lockman Representing the Collaboration. Introduction Lifetime difference measurement Mixing in Wrong sign D 0 → K + p - and D 0 →K + p - p 0 decays Time-integrated CPV measurements Radiative D 0 decays Summary.

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Charm Mixing, CPV and Rare D 0 decays at BaBar

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  1. Charm Mixing, CPV and Rare D0 decays at BaBar William S. Lockman Representing the Collaboration Introduction Lifetime difference measurement Mixing in Wrong sign D0→K+p- and D0→K+p-p0 decays Time-integrated CPV measurements Radiative D0 decays Summary PANIC 2008: International Conference on Particles and Nuclei November 9-14, 2008 Eilat, Israel

  2. Long distance amplitudes predominantbut hard to quantify • Recent estimates: |x| ≤ 1%, |y| ≤ 1%consistent with current observations pp KK Kp ... A. Petrov,Int.J.Mod.Phys.A21:5686 (2006). Introduction • Mixing and CPV in the D0 system were discussed over 30 years ago A. Pais and Treiman, Phys. Rev. D12, 2744 (1975) • But evidence for D0 mixing only recently observed: • Of all the neutral mesons, the D system exhibits the least mixing • New Physics signature: CPV • short distanceDC=2 suppression: • D mixing loop involves d-type quarks • b quark loop suppressed: • s and d quark loops: GIM suppressed • Mass difference ampl. < O(10-5) E. Golowich, J. Hewett, S. Pakvasa, A. Petrov, Phys. Rev. D76 095009 (2007) W. Lockman

  3. Flavor state Mixing and CPV Schroedinger eqn governs time evolution (off diagonal M and  elements determine mixing) • Flavor eigenstates can mix through weak interaction: • Physical eigenstates D1 and D2 ≠ flavor eigenstates • In the limit of CP conservation: D1 = CP D2 = CP • If weak interaction splits the masses or widths of physical eigenstates, flavor state mixing will occur • Two parameters characterizing mixing: • where M1,2 and G1,2 are the masses and widths of physical states, resp. • The mixing rate is RM= (x2+y2)/2 • CPV in mixing is characterized by the asymmetrywhere + (-) indicates an initial D0 (D0) W. Lockman

  4. New Result • Not today BaBar BELLE CLEO-c CDF Recent Measurements • Mixing measurements: • D0K+K-, p+p- • D0K+p- • D0K(*)-l+n • D0K+p- p0 • D0Ksp+p- • D0KsK+K- • Quantum Correlations • Search for time integrated CPV: • D0K+K-, p+p- • D0p+p-p0, K+K-p0 • D+K+K-p+ W. Lockman

  5. Lifetime difference measurements • Using D*+→p+D0 decays, we measure the lifetimes of • CP-mixed D0K Cabibbo-favored (CF) decays and • CP-even D0KK andp+p- singly Cabibbo-suppressed SCSdecays • This allows a estimation of by • where and + (-) indicates an initial D0 (D0) • We also measure the CP asymmetry: • Relation to mixing parameters: • where AM is the mixing rate asymmetry and f characterizes CPV in the interference between mixing and decay • In the limit of CP conservation, yCP = y and DY=0 W. Lockman

  6. Decay time fits to determine (yCP, Y) =409.3±0.7 fs =401.3±2.5 fs =404.5±2.5 fs =407.6±3.7 fs =407.3±3.8 fs K and KK lifetimes differ! W. Lockman

  7. Lifetime Difference Results 3.2  evidence - no CPV PRL 98 211803 (2007) 540 fb-1 3.0  evidence - no CPV PRD 78 011105(R) (2008) 384 fb-1 HFAG World Average:yCP = (1.072 ± 0.257 )% arXiv 0808:1297 (2008) Combining 384 /fb tagged and 91 /fb untagged (BaBar): yCP = (1.03 ± 0.33(stat.) ± 0.19(syst.))% W. Lockman

  8. D0 D0 D0f f D0 D0 f Mixing in “Wrong Sign” Decays (D0→K+p-) • Two types of WS Decays: • Doubly Cabbibo-supressed (DCS) • Mixing followed by Cabibbo-Favored (CF) decay Two ways to reach same final state interference! Discriminate between DCS and Mixing decays by their proper time evolution (assuming CP-conservation and|x|«1, |y|«1) : DCS decay Mixing Interference between DCS and mixing K : strong phase difference between CF and DCS decay amplitudes W. Lockman

  9. 1.5 fb-1 PRL 100,121802 (2008) 384 fb-1 PRL 98,211802 (2007) 3.8  3.9  Observations of Mixing in D0→K+p- Evidence for mixing from BaBar (3.9s) and confirmation by CDF (3.8s) Two completely different experiments (BaBar and CDF) yield nearly identical results: W. Lockman

  10. D0 D0 D0f f D0 D0 f DCS Interference Mixing Mixing in WS D0 K+-0 Decays • Analysis formally similar to to wrong sign D0 K+- analysis but now mixing depends on position in Dalitz plot. • Final state can be reached in two ways, yielding sensitivity to mixing by through analysisof the time dependent WS decay rate (|x|,|y|<<1): • The measured mixing parameters are: 384 fb-1 – new result: arXiv:0807, 4544 [hep-ex], submitted to PRL where = phase difference between DCS D0→rK+ and CF D0→rK+ reference amplitudes (and cannot be determined in this analysis) W. Lockman

  11. WS Dalitz plot 3K events RS Dalitz plot ~660K ev. signal box: 0.1449<Dm<0.1459 GeV/c2 1.8495<mKpp<1.8795 GeV/c2 RS signal purity: 99% WS signal purity: 50% Mixing in WS D0 K+-0 Decays • Find CF amplitude from time-integrated fit to RS Dalitz plot • isobar model expansion • Use this in time-dependent fit to WS plot to determine and mixing parameters. • Results: • No evidence for CPV • Main systematics: • Dalitz plot model • Event selection criteria • Signal and background yields W. Lockman

  12. Time integrated CPV • Two diagrams (tree and penguin) in SCS decays can lead to CPV • Measured asymmetry includes direct and indirect terms • SM predictions for ACP are tiny: O(0.001% - 0.01%) • observation of ACP at ~0.1% level would indicate NP • Whereas previous measurements of ACP had uncertainties of ~(1-10)%,recent improvements in controlling experimental systematicshave led to reduced errors ~(0.2-0.4)% on ACP F. Bucella et al., Phys. Rev. D51, 3478 (1995) S. Bianco et al., Riv. Nuovo Cim. 26N7, 1(2003) S. Bianco, F.L. Fabbri, D. Benson, and I. Bigi, Riv., Nuovo Cim. 26N7, 1 (2003). A.A. Petrov, Phys. Rev. D69, 111901 (2004) Y. Grossman, A.L. Kagan, and Y. Nir, Phys. Rev. D75,036008 (2007) W. Lockman

  13. Experimental Procedure • Measure the time integrated CP asymmetries • Relative ps+ and ps- tracking efficiencies not equal • Use D0→K-p+ tagged and untagged data to determine this • Due to Z/g interference and radiative corrections D0and D0are produced with a forward backward asymmetry in C.M. polar angle q* • compute the D0 -D0 flavor asymmetry vs cos in the center of mass • extract Acp and Afb by constructing even and odd functions of cos W. Lockman

  14. Time integrated CPV in D0 KK,  BaBar data sample 384 fb-1 PRL 100 061803 (2008) • No evidence for CP violation in either mode • 2-3x improvement on 2006 world average errors: W. Lockman

  15. Search for CPV in D0 KK0, 0 phase space integrated asymmetries: Phys. Rev. D78 051102 (2008) No evidence of CP violation in either decay mode. No significant difference between modes Used technique described earlier to correct for tracking asymmetries W. Lockman

  16. New HFAG Average for ICHEP08http://www.slac.stanford.edu/xorg/hfag/charm/index.html arXiv:0808.1297 No-CPV point still allowed at 1σ No-mixing point excluded at 9.8σ W. Lockman

  17. Radiative D0→fg and K*g Decays D0→fg Cabibbo suppressed, D0→K*0g Cabibbo favored radiative D0 decays dominated by long range processes Results: Phys. Rev. D78, 071101 (2008) Vector Meson Dominance pole diagrams: o = weak transition P = pseudoscalar meson Using world average B(D0→K-p+)=(3.89±0.05)%: new W. Lockman

  18. Summary • After 30 years of searching for it, the collective evidence forD0 mixing is becoming compelling • The no-mixing point is excluded at ~10s, including systematic uncertainties • However, no single measurement exceeds 5s • BaBar will be adding more measurements soon • Average values of the mixing parameters are x~1 %, y~0.8 % • compatible with the upper range of standard model predictions • No evidence for CPV at the current experimental sensitivity (~0.25 %) • systematic uncertainties are likely to diminish as more B-factory data is analyzed • Theoretical predictions in accord with measured branching fractions W. Lockman

  19. Extra W. Lockman

  20. BaBar Generic Mixing Analysis Identify the D0 flavor at production using the decays • select events around the expected • The charge of the soft pion determines the flavor of the D0 Identify the D0 flavor at decay using the charge of the Kaon Vertexing with beam spot constraint determines decay time, and decay time error, D0 decay vertex Beam spot: x~ 100 m, y~ 6 m right-sign (RS) wrong-sign (WS) D0 production vertex W. Lockman

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