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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. New Result. Reviewed Here. Recent Measurements. Mixing measurements D 0 K + K - , p + p - D 0 K + p - D 0 K (*)- l + n D 0 K + p - p 0 D 0 K s p + p - Quantum Corr.

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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, U. Cincinnati

  2. New Result Reviewed Here Recent Measurements • Mixing measurements • D0K+K-, p+p- • D0K+p- • D0K(*)-l+n • D0K+p- p0 • D0Ksp+p- • 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. 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 smallest mixing • 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 result: PRD 69,114021 (Falk, Grossman, Ligeti, Nir & Petrov) (consistent with current observation) Signals for New Physics would be |x |>>|y | or Evidence for CPV 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  RWS/RRS 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 Brian Meadows, U. Cincinnati

  9. 384 fb-1 – New Result arXiv:0807.4544 [hep-ex] D0 K+-0Time-Dependent Amplitude Analysis • Similar to D0 K+- but now is an amplitude at a point in the Dalitz plot (DP) describing the K+-0 phase space • Again, CF ( ) and DCS ( ) amplitudes contribute to decay and describe density of points in the DP at time t: • The interference term permits measurement of assumes DCS-Mixing interference Mixing DCS Depends on DP position NOTE K= 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+ D0 only: D0 only: Probability for no mixing 0.1% (3.2) No evidence for CPV 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. Brian Meadows, U. Cincinnati

  11. 534410§ 830 Events 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 that 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. Time-Integrated CPV • CPVin the charm sector is expected to be small in the SM Above the 0.1% level, it would probably be a NP signal. • Current experimental sensitivity is close to this level. • Experimentally we measure the decay rate asymmetry which includes both direct and indirect contributions. • Previous asymmetries were ~0% with uncertainties ~(1-10)% • Recent data exist for , K+K- and for 0 and K+K-0 from Babar and Belle that, with increased statistical precision and new insight on systematics, improve uncertainties  ~(0.2-0.4)%. = A~0. 01% • 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) Brian Meadows, U. Cincinnati

  13. D0 K+K- and +- • 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) • Evaluate number of events (with weights above) in cos* bins • 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 ACP Brian Meadows, U. Cincinnati

  14. 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

  15. CPV in 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: Phys.Lett.B662:102-110,2008 Phys.Rev.D (TBP, 2008) 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

  16. CPV in D0-+0 and K-K+0 • Babar also exploited three potent advantages of search in 3-body modes: • CPV is unlikely to be in all channels – but perhaps in one Can search each channel - e.g. D0 [P-wave +-] + 0 • Systematic uncertainties from s+ tagging or from production asymmetries become 2nd o`rder effects Each channel can be normalized to whole Dalitz plot. • 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

  17. 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

  18. 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

  19. Summary No-mixing point excluded at 6.7σ No-CPV point still allowed at 1σ • Schwartz, • arXiv:0803.0082 • After 30 years looking, evidence for D0 mixing is now compelling • No evidence for CPV at current experimental sensitivity • Systematic uncertainties scale with luminosity at B factories x = (0.97 +0.27 −0.29 )%,                     y = (0.78 +0.18 −0.19 )%, δ = (0.38 +0.20 −0.22 ) radian,         δ2 = (0.57 +0.44 −0.45 ) radian, RD = (0.335 ± 0.009)%,                     AD = (−2.2 ± 2.5)%, |q/p| = 0.86 +0.18 −0.15   ,                  φ = (−0.17 +0.14 −0.16 ) radians. Brian Meadows, U. Cincinnati

  20. 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

  21. 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

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

  23. 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

  24. 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

  25. 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

  26. D0 D0 (D0 f) D0 f (D0 f) CPV and Decays of Neutral D Mesons • In absence of CPV • so • D1isCP -even and D2isCP -odd • CPV can come from either the mixing , or from the decay (or both) • To distinguish, it is necessary to measure phase of f for a variety of different f’s. strong weak Unlikely, before Super B ! Brian Meadows, U. Cincinnati

  27. Lifetime Ratio Data 384 fb-170K events (99.6% purity) 540 fb-1111K events (98% purity) • Many systematic effects cancel in the ratio of lifetimes wrt D0  K-+ decay mode. • BUT backgrounds differ considerably  were kept as low as possible • D*D0+ was used to tag the D flavour and to reduce background • BaBar samples were slightly smaller, but purities were higher. Brian Meadows, U. Cincinnati

  28. 3.0  evidence - no CPV Lifetime Ratio Results arXiv:0712.2249 Accepted by PRL PRL 98:211803,2007 3.2  evidence - no CPV Brian Meadows, U. Cincinnati

  29. Results of WS D0K+- Measurements • All three experiments compared fits with no Mixing or CPV • Babar and Belle made fits to include possibility for CPV Evidence for Mixing is clear, but there is no evidence for CPV. Need independent measurement of K to extract x or y from these results. Brian Meadows, U. Cincinnati

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

  31. 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: • Then the D0 and D0 evolve in time in a non-exponential way Eigenvaluesare with means: Brian Meadows, U. Cincinnati

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