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Mixing and CPV in the D System Current Situation and the Task for Super B

Mixing and CPV in the D System Current Situation and the Task for Super B. Mixing in the D system Prospects for Super B and Super D ? Time-integrated CP violation (CPV) Summary. New Result. Mixing Observed. Most Recent Measurements. Mixing measurements D 0 K + K - , p + p -

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Mixing and CPV in the D System Current Situation and the Task for Super B

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  1. Mixing and CPV in the D SystemCurrent Situation and the Task for Super B • Mixing in the D system • Prospects for Super B • and Super D ? • Time-integrated CP violation (CPV) • Summary Brian Meadows, U. Cincinnati

  2. New Result Mixing Observed Most 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 Brian Meadows, U. Cincinnati

  3. Mixing in the D System • 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 A. Pais and S.B. Treiman, Phys. Rev. D12, 2744 (1975). Brian Meadows, U. Cincinnati

  4. Mixing in Standard Model • Off-diagonal mass matrix elements have two components: C=2 (short-range) (contributes mostly to x) 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 results: • (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

  5. General Agreement … … Signals for New Physics would be |x |>>|y |OR Evidence for CPV Brian Meadows, U. Cincinnati

  6. 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

  7. 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

  8. Lifetime Difference Results yC P world average from HFAG A. Schwartz, arXiv:0803.0082 (updated) 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

  9. Mixing K+- D0 “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- + • Processes interfere: • Mixing then Cabibbo-favoured (CF) decay • Doubly-Cabibbo-Suppressed (DCS) decay 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

  10. 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

  11. 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 toD0 K+-but now is an amplitude at a point in the Dalitz describing theK+-0phase space • CF( ) andDCS( ) amplitudes contribute to decay and describe density of points in theDPat timet: • The interference term permits measurement of NOTE K=  is also unknown Brian Meadows, U. Cincinnati

  12. WS Dalitz plot 3K events RS Dalitz plot ~660K ev. 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

  13. 534410§ 830 Events Time-Dependent Amplitude Analysis of D0 Ks+- PRD72:012001 (2005) 9 fb-1 PRL 98:211803 (2007) 540 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

  14. Measurement of yCPin D0→K0SK+K- decays Phys.Lett.B670:190-195 (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 Brian Meadows, U. Cincinnati

  15. No-mixing point excluded at ~9σ No-CPV point still allowed at 1σ A. Schwartz, et al arXiv:0803.0082 (updated) HFAG Mixing Summary • The HFAG collaboration have combined a wide range of these and other measurements to extract mixing parameters and 2 contours: Brian Meadows, U. Cincinnati

  16. What Could SuperB Do? Major Goals: • Establish whether or not there is any CPV • Improve precision of these measurements • Compare (x,y) for D0 and D0 • Examine whether CPV originates from the mixing (p = q) or from decay Af = Af ? Possible Strategy: • Compare (x,y) for D0 with (x,y) for D0 • Compare different decay channels (is CPV in mixing or in decay?) Brian Meadows, U. Cincinnati

  17. Improve Precision – Projection to SuperB • Assumptions: • Central values are as reported at ICHEP2008 • Scaling is done only for D0 K-+, D0Ks+- and  measurements. • Systematic errors scale as 1/sqrt(N) • The latter are mostly determined by data so this is approximately so. If central values persist: Will observe >> 5 effect !! No-CPV point still allowed at 1σ NOW x x (Alan Schwartz/David Asner – private communication) Brian Meadows, U. Cincinnati

  18. Running at y(3770) CLEO c were able to measure K-+ strong phase: from 281 pb-1 Main systematic uncertainty comes from p0 and h efficiency. Including other D mixing results:  SuperB 300 fb-1: Extend to Other Channels Use Quantum-Correlations (QC) AND – the possibilities are that we can use OTHER channels with knowledge of strong phases Brian Meadows, U. Cincinnati

  19. For multi-body channels, this means we can measure strong phases “integrated over” the final state. The “coherence” measures to what extent this is useful. CLEO measurements (using external mixing information from elsewhere): It is not clear how these will affect SuperB mixing results but strong mixing angles will be known to with a few degrees. QC in Multi-body Channels Brian Meadows, U. Cincinnati

  20. We need to interpret how improved SuperB measurements will propagate into mixing parameters. The main motivation in the measurements from CLEO c data by LHCb experimenters was for use in the determination of CKM  D-mixing parameters that were measured externally were used to determine ’s so we cannot use them as they come. Most obvious way: Extract D-mixing-independent cos  from CLEO c results Use the HFAG approach (perhaps use their tool for this) with appropriate scaling for cos . Evaluation of CLEO c QC Results Brian Meadows, U. Cincinnati

  21. m-2 (GeV2/c4) m02 (GeV2/c4) Time-Integrated QC in Multi-body Channels • For multi-body channels, we could measure relative phases “bin-by-bin” in their phase-space. Quantum correlations remove necessity for model describing phase space. Probably ONLY way to obtain a true PWA fit. X X For higher multiplicities, we would measure “coherence” and a single strong phase. For 3-body final states this provides model-independent measurement of strong phase variation over the Dalitz plot - Useful for  measurement Brian Meadows, U. Cincinnati

  22. m-2 (GeV2/c4) m02 (GeV2/c4) Time-dependent QC Decays - Super D? • The moving CMS means we could measure time-dependent (TD) strong phases resulting from D0 mixing. Leads to model-independent time-dependent phase space distribution. X X Boost is ~same as for Y(4S) Is this possible or useful ? Brian Meadows, U. Cincinnati

  23. Super D for Mixing? • Disadvantages wrt doing TD Dalitz plot analysis at Y(4S): • D0’s also have little transverse momentum at y(3770) so we rely on the boost - bg=p/m [~same as at Y(4S)] for time measurements • BUT tD0 << tB0 so s ~ 30 mm is only about one D0 lifetime • We only anticipate running for ~300 fb-1 (comparable to BaBar) • Advantages: • D0’s are produced at ~3 x the rate of B0’s at Y(4S) • D0 decay rates ~10-(3-4) are typically 100xB0’s  So there are many more “double-tags” than in B’s from Y(4S) • Nevertheless, CLEO have 420 double-tagged Ks+- events from 818 pb-1 that suggests “Super D” will only have ~ 160K • BaBar (and Belle) each have ~500K at Y(4S) – with superior time-resolution now. Brian Meadows, U. Cincinnati

  24. Super D for Mixing? • So, unless model-dependence is a major problem (not known to be) it does not appear that the Ks+-D mixing analysis will benefit from Super D option • Perhaps time-dependence of cos  (integrated over phase space)the 4-body channels could add mixing information ? Brian Meadows, U. Cincinnati

  25. Time-Integrated CPV Measurements Brian Meadows, U. Cincinnati.

  26. = A~0. 01% for f = K+K- or +- Time-Integrated CPV Measurements • 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 experimental insight has been able to improve systematic uncertainties  ~(0.2-0.4)%. • Previous asymmetries were~0%with uncertainties~(1-10)% Singly Cabbibbo-suppressed SCS decays allow penguin contributions  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) Brian Meadows, U. Cincinnati

  27. 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 Time-Integrated CPV Measurements • D0’s produced in e+e- collisions at Y(4S) were tagged by the sign of the slow pion from D* decay Two reasons WHY reaching the “per mille” level is a challenge : Brian Meadows, U. Cincinnati

  28. 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

  29. 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.D78:051102,2008 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

  30. CPV in D0-+0 and K-K+0 Phys.Rev.D78:051102,2008 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

  31. Time-Integrated CPV at Super B • Y(4S) DATA can be used to measure the charge-asymmetry of efficiency • This means that the major systematic uncertainties scale with luminosity. • So we may be sensitive to CPV below the 0.1% level where SM backgrounds probably exist. • An important test is to see if • If so, this would signify that CPV was “direct”. Caution: An important assumption made at BaBar (and Belle) was one of -symmetry. • An End-cap PID system will probably not preserve this symmetry and may not be usable for CPV measurements Brian Meadows, U. Cincinnati

  32. Time-Integrated CPV at D Threshold Example from CLEO-c: D+K-K++ • 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 - Limited by MC study Of Charge Asymm efficiency Phys. Rev. D78:072003 (2008) 818 pb-1 Brian Meadows, U. Cincinnati

  33. CLEO-c: D+K-K++ • Fundamental problem is how they measured § charge asymmetry in tracking and reconstruction efficiency. • CLEO-c used Monte Carlo model of their efficiency - Probably not precise enough for a 0.1% measurement ? - Will need to find a way to use data instead ? • At “Super D”, the laboratory will not be the CMS - production asymmetry will need to be removed as in the BaBar measurements. Brian Meadows, U. Cincinnati

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

  35. Brian Meadows, U. Cincinnati

  36. How This Helps at Super B • We will measure cos  more precisely, making measurements of x’2, y’ interpretable directly as x and y • In effect, this is what HFAG do in their averaging procedure, now. • We can extend these measurements to other channels • Will improve sensitivity to CPV (if it is present) • Will make a study of the origin of CPV possible Brian Meadows, U. Cincinnati

  37. D0 K+K- and +- • D0’s produced in e+e- collisions 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

  38. 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

  39. 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

  40. Mixing and Quantum-Correlations Brian Meadows, U. Cincinnati

  41. m-2 (GeV2/c4) m02 (GeV2/c4) Future Prospects • NP could well show up in the charm sector, and could help in interpretation of results from LHC Direct CPV in SCS decays have systematic uncertainties that mostly scale with increasing luminosity Time-dependent Quantum-correlated Decays ! Mixing results are already interesting wrt p/q Suppose we could measure this ratio for different decay modes Quantum correlations in a moving CMS would allow time-dependent effects to be measured. Should we build a Super B Factory with 100x luminosity ? Brian Meadows, U. Cincinnati

  42. 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

  43. 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

  44. 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

  45. Why is Charm Mixing Interesting • Main reason is that short distance effects come from loops with d-type quarks in them: • SM Mass difference ampl. < O(10-5) • Long distance mixing amplitudes • predominant but hard to quantify • Theoretical estimates typically |x|<1%, |y|<1% (consistent with exp.) • b quark loop suppressed: • s and d quark loops: GIM suppressed In the SM, CPV would have to originate in the 2x2 sector of the CKM • General agreement: Signals for New Physics would be |x |>>|y |OR Evidence for CPV Brian Meadows, U. Cincinnati

  46. 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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