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Mixing and CPV in the D System

Mixing and CPV in the D System. Introduction Mixing in the D system Time-integrated CP violation (CPV) Summary Brian Meadows for the Collaboration. New Result. Not today. Recent Measurements. Mixing measurements D 0 K + K - , p + p - D 0 K + p - D 0 K (*)- l + n

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Mixing and CPV in the D System

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  1. Mixing and CPV in the D System • Introduction • Mixing in the D system • Time-integrated CP violation (CPV) • Summary Brian Meadows for the Collaboration Brian Meadows, U. Cincinnati

  2. New Result Not today 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 Corr. • Search for time integrated CP violation (CPV) • D0K+K-, p+p- • D0p+p-p0, K+K-p0 • D+K+K-p+ Brian Meadows, U. Cincinnati

  3. Short distance DC=2 SM 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) • Long distance mixing amplitudes predominant but hard to quantify Recent estimates are typically (consistent with current observation) Signals for New Physics would be |x |>>|y | or Evidence for CPV Golowich, Hewett, Pakvasa an Petrov, PR 76, 095009(2007) Introduction A. Pais and S.B. Treiman, Phys. Rev. D12, 2744 (1975). • Mixing and CPV in the D0 system were discussed over 30 years ago! • BUT evidence for mixing was only recently found • Of all neutral mesons, the D0 system exhibits the least mixing Brian Meadows, U. Cincinnati

  4. D0 D0 (D0 f) Mixing Parameters • Mixing in the neutral D system arises from the existence of two mass eigenstates D1 and D2 that are not flavour states • It is usual to define four mixing parameters: • CPV from either the mixing, or from the decay (or both) can ocur Eigenvaluesare with means: CPV signalled by D0 f strong weak (D0 f) Brian Meadows, U. Cincinnati

  5. Lifetime Difference Measurements • In the absence of CPV, D1 is CP-even and D2 is CP-odd • Measurement of lifetimes  for D0 decays to CP-even and CP-odd final states lead to a measurement for y. • Allowing for CPV, measure the D0 and D0 asymmetry Mixed CP. Assumeis mean ofCP-evenandCP -odd K +K –or+- CP -even • PRD 69,114021 (Falk, Grossman, Ligeti, Nir & Petrov) Brian Meadows, U. Cincinnati

  6. Lifetime Difference Results yC P world average from HFAG A. Schwartz, arXiv:0803.0082 3.2  evidence - no CPV PRL 98:211803,2007 540 fb-1 3.0  evidence - no CPV arXiv:0712.2249 384 fb-1 Accepted by PRL yCP = (1.132  0.266)% 384 /fb tagged and 91 /fb untagged (BaBar) Brian Meadows, U. Cincinnati

  7. “Wrong-sign” (WS) Decays (D0 K+-) • Tag flavour of D0 by decay D*+ D0+ • Measure time-dependence of rates RWS for wrong-sign WSdecays D0 K+ - compared to right-sign RRS decays D0 K- + Mixing • Processes interfere: • Mixing then Cabibbo-favoured (CF) decay • Doubly-Cabibbo-Suppressed (DCS) decay K+- D0 DCS-Mixing interference DCS rate Mixing rate assumes Strong phase  unknown. Define x’ = x cos  + y sin  y’ = y cos  - x sin  Can only measure x ’2 and y ’ /|f|2 ~ 10-3 Brian Meadows, U. Cincinnati

  8. 400 fb-1 PRL 96,151801 (2006) 1.5 fb-1 PRL 100,121802 (2008) 384 fb-1 PRL 98,211802 (2007) 2.0  3.8  3.9  Observations of Mixing in D0 K+- • Though Belle’s result was most sensitive, they were unable to claim observation. • Both Babar and CDF obtained central values forx’2<0 • Mixing signals seen in the time-dependence of the RWS/RRS ratio x`2 ~ 0 y ~ 1% RWS/RRS Brian Meadows, U. Cincinnati

  9. 384 fb-1 – New Result arXiv:0807.4544 [hep-ex] assumes DCS-Mixing interference DCS Mixing Depends on DP position Time-Dependent Amplitude Analysis of D0 K+-0 • Similar to D0 K+- but now is an amplitude at a point in the Dalitz plot (DP) describing the K+-0 phase space • CF ( ) and DCS ( ) amplitudes contribute to decay and describe density of points in the DP at time t: • The interference term permits measurement of NOTE K=  is also unknown Brian Meadows, U. Cincinnati

  10. WS Dalitz plot 3K events RS Dalitz plot ~660K ev. t S13=m2K0 S13=m2K+ Probability for no mixing 0.1% (3.2) Evidence for Mixing in (WS) D0 K+-0 • Use D*- tagged sample • 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. D0 only: D0 only: No evidence for CPV Brian Meadows, U. Cincinnati

  11. 534410§ 830 Events Time-Dependent Amplitude Analysis of D0 Ks+- PRL 98:211803 (2007) 540 fb-1 PRD72:012001 (2005) 9 fb-1 • Here, it is possible to measure x, y, |p/q| and arg {p/q} the D0-D0 strong phase is fixed by presence of CP eigenstates in f • Strong phases of all points relative to CP eigenstates measured by time-dependent amplitude analysis of the DP. NOTE – this is smaller than yCP Previous result from CLEO (9 fb-1) (−4.7 < x < 8.6)% (−6.1 < y < 3.5)% at 95% CL. Mixing only at 2.4  level. Hint that x > y ?? Brian Meadows, U. Cincinnati

  12. Measurement of yCPin D0→K0SK+K- decays Arxiv:0807.0148v1 (2008) 673 fb-1 NEW • In effect, this is a measurement of lifetime  in CP=+1 and CP=-1 parts of the K0sK+K- Dalitz plot. • Choose Ks0region and its sidebands • Fractions f of CP-even final state in each region: A+and A-areCP-even and odd amplitudes describing Dalitz plot population. 139K untagged Events m2KK(GeV/c2)2 over appropriate mK+K-range Belle preliminary! Brian Meadows, U. Cincinnati

  13. Time-Integrated CPV • CPV in the charm sector is expected to be small in the SM. If it is measured to be above the 0.1% level, it would signal NP. • Experimentally we measure the decay rate asymmetry which includes both direct and indirect contributions. • New insight on systematics, improve uncertainties  ~(0.2-0.4)%. • Previous asymmetries were~0%with uncertainties~(1-10)% Singly Cabbibbo-suppressed SCS decays allow penguins  can lead to CPV 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) = A~0. 01% Brian Meadows, U. Cincinnati

  14. D0 K+K-, K+K-0, +- and +-0 • D0’s produced in e+e- collisions at B factories are tagged by the sign of the slow pion from D* decay Two reasons reaching the “per mille” level is a challenge : • Efficiencies fors+ands-are not the same Use DATA to find the asymmetry: • Use (several x106)untagged K -+to map efficiency asymmetry for K –and for+ • Repeat fortagged K -+to mapsasymmetry • D 0 ‘s are produced with asymmetry in * (relative to beam axis) and efficiency depends on * (from Z0/ and higher order effects) • Take average of each cos* range for |cos*| > 0 and < 0 as ACP • Take difference of each cos* range for |cos*| > 0 and < 0 as AFB Brian Meadows, U. Cincinnati

  15. D0 K+K- and +- Arxiv:0807.0148v1 (2008) NEW Phys.Rev.Lett.100:061803 (2008) • No evidence for CPV • Systematic uncertainties ~ 0.1% (Likely scale with luminosity-1/2) !! • No significant difference between KK and  Brian Meadows, U. Cincinnati

  16. D0-+0 and K-K+0 • There are two recent results on the CPV asymmetry measurement, integrated over the 3-body phase space for these channels: • Three search strategies (2 model-independent) for CPV in quasi two-body modes led to upper limit ~2%. Phys.Lett.B662:102-110,2008 532 fb-1 Phys.Rev.D (Accepted) 384 fb-1 Belle’s (earlier paper), did not do this. Babar used the technique described to correct for tracking asymmetries. • No evidence for CPV • Systematic uncertainties ~ 0.2% (Likely scale with luminosity-1/2) !! • No significant difference between KK  0 and  0 Brian Meadows, U. Cincinnati

  17. D+K-K++ Arxiv:0807.4545v1 (2008) 818 pb-1 • CLEO-c used 818 pb-1e+e- at the (3770) – nearD+D-threshold. • Tag one D§ to identify the other one • no asymmetry from D* tagging! • Laboratory system same as CMS • no production asymmetry. • Overall asymmetry • Amplitude analysis of Dalitz plot – integrated asymmetry D+K+K-+ x Tag D - Brian Meadows, U. Cincinnati

  18. Summary No-mixing point excluded at 6.7σ No-CPV point still allowed at 1σ A. Schwartz, et al arXiv:0803.0082 • After 30 years looking, evidence for D0 mixing is now compelling • We need mixing parameters for both D0 and D0 in more channels. • No evidence for CPV at current experimental sensitivity (~0.2%) • Systematic uncertainties scale with luminosity at B factories Brian Meadows, U. Cincinnati

  19. Back-up Slides Brian Meadows, U. Cincinnati

  20. CPV in D0-+0 and K-K+0 Phys.Rev.D (Accepted) 384 fb-1 • Exploited potential for extended search within these 3-body modes: • CPV is unlikely to be in all channels – but perhaps in one Search each channel - e.g. D0 0 + 0 • Each channel can be normalized to whole Dalitz plot. Systematic uncertainties from s+ tagging or from production asymmetries become 2nd o`rder effects • CPV is signalled by differences in phase behaviour between D0 and D0. Dalitz plot for these 3-body final states yields information on phase behaviour between channels. • BaBar used three search strategies • Two model-independent searches for CPV in exclusive parts of phase space. • A model-dependent search based on a to fit the Dalitz plot distributions Brian Meadows, U. Cincinnati

  21. Two Model-Independent Searches for CPV in D0-+0 and K-K+0 Phys.Rev.D (TBP, 2008) Dalitz plots for D0 and for D0 are normalized and compared, bin-for-bin Unbiassed frequentist test yields 16.6% conf. level there is no difference. Legendre polynomial moments up to order 8 for D0 and for D0 are normalized and compared, in each channel. Unbiassed frequentist test indicates 23-66% conf. level there are no differences in the various channels. [+-]+ 0 channel [+0]+ - channel Brian Meadows, U. Cincinnati

  22. Model-dependent Search for CPV in D0-+0 and K-K+0 Phys.Rev.D (TBP, 2008) Dalitz plots for D0 and for D0 were fitted to isobar model expansions of interfering amplitudes in each channel. Differences in magnitudes and phases For each amplitude were insignificant. Brian Meadows, U. Cincinnati

  23. Quantum-Correlated Method Brian Meadows, U. Cincinnati

  24. OFF OFF Measurement of yCPin D0→K0SK+K- decays Belle Time dependent decay rate: Compare lifetimes of D0 candidates measured in different m(K+K-) regions: ON Brian Meadows, U. Cincinnati

  25. Measurement of yCPin D0→K0SK+K- decays Belle Fit to the s0=m2(K+K-) distribution is performed using the Dalitz models given in PRD72, 052008 and arXiv:0804.2089. 139x103 flavor untagged D0→K0SK+K- reconstructed decays on a 673 fb-1 data sample. D0 lifetime is determined from the means of the proper decay time distributions of events populating the m(K0S)-m(K0SK+K-) signal window (SW) and sidebands (SB): Belle preliminary! Brian Meadows, U. Cincinnati

  26. D0 f D0 D0 D0 f D0 f Decays of Neutral D Mesons • When final state f is accessible to both D0 and D0, interference between mixing and direct decay will occur Which leads to a time-dependence for decay • The interference makes the mixing parameters measurable carry strong phase  between the decays and BUT, for this, it is essential to know the strong phase  Brian Meadows, U. Cincinnati

  27. Mixing in Standard Model • Off-diagonal mass matrix elements have two components: C (short-range) (contributes mostly to x) Via Hadronic intermediate states (long-range) • Difficult to compute (need to know all • the magnitudes and phases, …) • Most computations predict x and y • in the range 10-3–10-2and |x|<|y| • Recent result: • PRD 69,114021 (Falk, Grossman, Ligeti, Nir & Petrov) • (consistent with current observation) • Intermediate b :CKM-suppressed • Intermediate d, s: GIM-suppressed • (almost 2 orders of magnitude • less than current sensitivity) Virtually no CPV expected, as most contributions are from udsc sector of CKM Brian Meadows, U. Cincinnati

  28. Mixing Measurements • Five basic types of measurement are made: • Time-dependence of ratio of wrong-sign (WS) doubly-Cabibbo-suppressed (DCS) to right-sign (RS) Cabibbo-favoured (CF) decays • Time-dependent Dalitz plot analyses • Lifetime ratio for decays toCPeigenstates • Measurement ofWSsemi-leptonic decays • Quantum correlated rates in(3770)decays • In all bute), events are tagged asD0orD0at birth (t = 0) from the sign of the slow pion (s) inD*  D0 s Brian Meadows, U. Cincinnati

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