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Prospects for TDCPV in the Charm Sector

Prospects for TDCPV in the Charm Sector. Brian Meadows with Adrian Bevan and GIanluca Inguglia Workshop on Charm Physics at Threshold 21-23 October 2011 IHEP, Beijing. Prologue.

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Prospects for TDCPV in the Charm Sector

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  1. Prospects for TDCPV in the Charm Sector Brian Meadows with Adrian Bevan and GIanluca Inguglia Workshop on Charm Physics at Threshold 21-23 October 2011 IHEP, Beijing .

  2. Prologue One of the tools that is offered is the promise of a time-boosted machine that can run at the  (3770), the charm threshold One thought – to study what we would learn from a “sin2” measurement at a “D factory”. We approach this from a “B factory perspective” We notice a few details that will need extra care when >100x as much data becomes available. We learn that a true “sin2c” measurement is much harder for D’s than it was for B’s. We also realize, though, that such an analysis brings with it a fine way to measure the D0 “mixing phase” M. • We recall what Ikaros Bigi has often reminded us, • “The goal in charm physics is not just to observe CPV in D decays • - but also to understand its origin !”

  3. CKM Predictions A number of CKM predictions are compared to observables K,  Md,  Ms, BF(B), alpha, sin2, , Vcb, lattice, … Fits to measured values give values for CKM parameters: We take simple averages of two fits to predict cu triangle. It is important to check the CKM paradigm for up-type quarks as it has been in down-quark sector. • Significant discrepancies may exist: • sin2 ~3 low • BF(B) 2.7 high • Is CKM model in question? arXiv:1104.2117 [hep-ph]

  4. CPV and CKM CPV requires weak phases - in SM these come from CKM Buras parameters - Ensure unitarity of “bd” triangle at all orders in  For charm decays, most interest is in “cu” triangle. NOTE – phase ofVub is stilldespite5term O(3) OK O(5) Needed [Phys. Rev. D50, 3433 (1994)] qu W qd • Usually use Wolfenstein parameters • =sinC, A, ,  (c=Cabibbo angle) Expand in powers of . There are 6 unitarity triangles – most common is“bd ” Coordinates of apex of bd triangle Phase in Vcd appears at order 5

  5. Unitarity Triangles from CKM Fits NOTE that c is equal to  c+ c~900 bd triangle cu triangle

  6. Constraint on cu Triangle ? • Lengths of sides: • CKMUncertainty • |Vud| 0.022% • |Vcd| 4.8% • |Vub| 11% • |Vcb| 3.2% • |Vus| 1% • |Vcs| 3.5% gc=g ~6.5 x 10-4 c(0.0350) ac Vus*Vcs  1 Might improve SL decays of Ds with run at Ds threshold ?  Some measurement of c is needed to test CKM

  7. Decays to CP Eigenstates T CS W P

  8. D0 Decay Amplitudes To order 6 these are: Four out of five are complex ! Real Phase is O(6) Phase is -bc Phase is -bcbut ~6 • Phase is c, but only found • in penguin amplitude • unlikely to be able to check thatc= Most promising ? D0  hh (h = , K, , f0, …)

  9. D0 Mixing Flavour oscillations in the neutral D system arise from the propagation of two mass eigenstates D1 and D2 that comprise the flavour states It is usual to define four mixing parameters: CPV from either the mixing, or from the decay (or both) can occur Eigenvaluesare with means: CPV signalled by Define decay amplitudes: mixing Weak decay Strong decay

  10. We exploit interference between direct decays D0fCPand decays through mixing: The time-dependence for decay rates () for D0(D0) differ In decays to CP states, strong phase for D0is same as D0 so D0 Decays to CP Eigenstates (D0f) CP eigenstates are accessible to D0 or D0 D0 “fCP”: (D0f) Mix (D0D0) Weak decay mixing To measure weak phasef we need to knowM

  11. Time-Dependent CP Asymmetry Define this as Decay to CP eigenstate dominated by single process, |f|=1 For B decay (y=0) this would be

  12. Time-Dependent CP Asymmetry Experimentally, we measure CP asymmetry vs. decay time • The D0 asymmetry is much smaller than that for B0 • |ACP | is almost linear in t while, for B0 it is sinusoidal • Slope of line depends upon = Arg {} • |ACP | is largest at large |t| • But as |t| grows larger, the number of events falls off exponentially.

  13. Mis-Tagging • Effect of mis-tagging probability  is to reduce the D0-D0 asymmetry • Effect of CP asymmetry in  is to shift the asymmetry. • Direct CPV asymmetry is measured at t=0 ! So shift is particularly serious in this case.

  14. Effect of mis-tagging probability  is to reduce the D0-D0 asymmetry Effect of CP asymmetry in  is to shift the asymmetry. Direct CPV asymmetry is measured at t=0 ! So shift is particularly serious in this case.

  15. Mis-Tagging Effect of mis-tagging probability  is to reduce the D0-D0 asymmetry Effect of CP asymmetry in  is to shift the asymmetry. Direct CPV asymmetry is measured at t=0 ! So shift is particularly serious in this case.

  16. Effect of “yB” on CP Asymmetry In Babar, it was assumed, in the measurement of S=sin2 from B0 decays, that yB = 0.0. The PDG specifies a value of ~0.01 § 0.035 Assuming this is Gaussian it will make a difference to S=sin2 of ~0.007 § 0.027 This is comparable to the expected precision of measurements from LHCb and SuperB Part of B 0 oscillation S-sin2 scale factor

  17. Outline CPV in the SM Mixing in neutral D system - why it matters Evidence for mixing BaBar / Belle Projections to SuperB/Belle2 and LHCb New approach to CPV in mixing? Prospects for observing CPV in decay

  18. Outline Mixing in neutral D system - why it matters Evidence for mixing BaBar / Belle Projections to SuperB/Belle2 and LHCb New approach to CPV in mixing? Prospects for observing CPV in decay

  19. Mixing Parameters Flavour oscillations in the neutral D system arise from the propagation of two mass eigenstates D1 and D2 that comprise the flavour states It is usual to define four mixing parameters: CPV from either the mixing, or from the decay (or both) can occur Eigenvaluesare with means: CPV signalled by Define decay amplitudes: Weak decay mixing strong

  20. Mixing in Standard Model is Very Small Off-diagonal mass matrix element – two leading terms: C=2 (short-range) (contributes mostly to x ) Hadronic intermediate states (long-range) C=1 C=1 • 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 predictions: • (consistent with current observation) • Down-type quarks in loop: • b : CKM-suppressed (|VubVcb|2) • d, s: GIM-suppressed • (almost 2 orders of magnitude less than current sensitivity) xD, yD at 1% consistent with SM, BUT CPV at 10-3 levels would be signal for NP

  21. All current measurements, so far, exploit interference between direct decays D0fand decays through mixing: Time-dependence to 2nd order in x and y. Mixing Measurements (D0f) D0 “f”: (D0f) Mix (D0D0) Interference  = f (s1,s2 ) + 0 §M CPV in Mixing Generally unknown “+” for D0 “ -” for D0 Accessible to D0 or D0 K (WS), point on DP, etc Decay through Mixing Direct decay Depends on DP decay model

  22. Mixing Measurements Interference term is approximately linear in xD, yD (small quantities) DP model defines f (s1,s2) BUT,since 0is unknown, only possible to measure rotated quantities x’D= xDcos 0 + yDsin 0AND y’D= yDcos 0 - xDsin 0 unless measurements off from charm threshold are available.

  23. Outline Mixing (particle - anti-particle oscillations). Brief review of evidence for mixing A New result Prospects for observing CPV in mixing

  24. Wrong Sign (WS) Decays D 0K+ - The WS decay rate RWS is: Since |f |>>1, all three terms are comparable For “right-sign” (RS) decays D0 K - + though, |f|<<1, so 2nd two terms are negligible and RRS is approximately exponential. Decay through Mixing Direct decay Interference

  25. Evidence for Mixing in D0 K+- 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  Mixing seen by Babar and CDF in time-dependence of the RWS/RRS ratio No Mixing RWS/RRS No Mixing + + + Belle result was the most sensitive, BUT evidence for mixing not significant !

  26. Mixing and CPV Parameters for D0 K+- Consistent with zero Same for D0 and D0

  27. In the absence of CPV, D1isCP-even andD2isCP-odd Measurement of lifetimes  for D0 decays to CP-even and CP-odd final states lead to a measurement of y ! Allowing for CPV, measure the D0 and D0 asymmetry Lifetime Ratio Measurements Mixed CP. Assumeis mean ofCP-evenandCP -odd K +K –or+- CP -even • PRD 69,114021 (Falk, Grossman, Ligeti, Nir & Petrov)

  28. Lifetime Ratio (Untagged D0’s) 263K events K 2,710K events KK KK K 70K events 731K events Tagged Sample– 384 fb-1 (for comparison) Recent result Phys.Rev.D80:071103,2009 – 384 fb-1 • Untagged K+K- decays are used • Two main backgrounds • Combinatorial (largest) Examined in sidebands • From “broken charm” (small) Examined in simulations (MC) • Fit decay time in narrow region Fit decay time Fit decay time • These are dis-joint samples of K and KK decays – untagged much larger • For each K and KK pair, selection & reconstruction systematics ~cancel.

  29. Fit t to exponential convoluted with resolution KKNOT same asK K KK 405.85 ± 1.00 fs 410.39 ±0.38 fs Assuming correlation between systematic uncertainties is 100% • Major systematic uncertainties: • Time-dependence of Combinatorial background 0.115 % • Time-dependence of Charm background 0.086 % • Signal mass window 0.110 % • Detector effects (alignment) 0.093 % Results: UNTAGGEDyCP = [1.12  0.26 (stat.)  0.22 (syst.)]%(3.3  evidence) TAGGEDyCP = [1.24  0.39 (stat.)  0.13 (syst.)]%(3.0  evidence) AVERAGEyCP = [1.16  0.22 (stat.)  0.18 (syst.)]%(4.1  evidence)

  30. HFAG World Average for yCP A. Schwartz, et al. (updated, EPS 2009) 540 fb-1 tagged 3.2  Effect First evidence In this mode 384 fb-1 tagged and untagged Combined 4.1  Effect Supercedes earlier BaBar results. yCP = (1.107  0.217)% A= -A¿ = (0.123  0.248)%

  31. Time-Dependent Amplitude Analysis of D0K+-0 Again, for , decay rate RWS is: Mixing D0 Phys.Rev.Lett.103:211801,2009 – 384 fb-1 • Similar toD 0K + -EXCEPT: fis now point in the Dalitz Plot X Models for WS ( ) and RS ( ) decay amplitudes define and BUT Comes from the model. Depends on position in Dalitz Plot Unknown constant • So the interference term permits measurement of x’’ = x cos K+ y sin KANDy’’ = y cos K- x sin K

  32. Evidence for Mixing - (WS) Tagged D0K+-0 WS Dalitz plot 3K events RS Dalitz plot ~660K ev. Significance of mixing signal 3.2 • Find CF amplitude from time-integrated fit to RS Dalitz plot • isobar model expansion • Use this in time-dependent amplitude analysis of WS plot  and mixing parameters. RS WS D0 only: D0 only: No evidence for CPV

  33. Outline Mixing (particle - anti-particle oscillations). Brief review of evidence for mixing A New result Prospects for observing CPV in mixing

  34. Amplitude Analysis of D0(t)KSh+h- Similar to D0K+ - 0BUT final states areself-conjugate (sum of odd and even CP-eigenstates): “Unknown” overall strong phase “K” is zero So xD and yD can be determined directly Dalitz plot described by decay amplitude If there is no direct CPV, then Can also determine |q/p| and arg{q/p}. Method pioneered by CLEO: Phys.Rev.D72:012001,2005 Used with 60x data by Belle: Phys.Rev.Lett.99:131803,2007

  35. Mean decay time differs by t - depends upon position in Dalitz plot Sensitivity to xD and yD also depends on density of points Productt N½ is maximum inWS K*and inbands RS K*  WS K* NEW result Amplitude Analysis of D0(t)KSh+h- Phys.Rev.Lett.105:081803 (2010) – 468.5 fb-1 RS K*  D0 WS K*

  36. t (ps) t (ps) Large and pure samples from D*+D0+decays fit to combined Ks and KsKK samples give most precise measurement to date Ks +- Signal : 541K purity 98.5% S-wave +- S-wave K0- P- and D-waves K-matrix model LASS model Breit-Wigner model KsK+K- Signal : 80K purity 99.2% S-wave K+K-Coupled-channel Breit-Wigner a0(980) All other waves Breit-Wigners

  37. Comparison with Previous Analyses • Third error is irreducible model ( ) uncertainty (IMU): ~10-3 in xD and yD ~8% in |q/p| and ~30 in arg{q/p}.

  38. HFAG Mixing Summary The HFAG collaboration combine 30 “mixing observables” to extract the 8 underlying mixing parameters and their 2 contours: A. Schwartz et al. arXiv:0803.0082 (updated FPCP 2010) X X No Mixing No CPV New D0 Ks+-+ KsK +K - results from BaBar significantly reduce average x Evidence for mixing is >10 No evidence for CPV

  39. Outline Mixing (particle - anti-particle oscillations). Brief review of evidence for mixing A New result Prospects for observing CPV in mixing

  40. Prospects for Observing CPV in Mixing The experimental challenge is shifted to observing CPV AND to investigating whether it is in mixing, decay or both. Best strategy may be to improve precision in xD & yD - say to ~1x10-4 D0-D0 asymmetries ~ |q/p|2-1 Several possibilities for this exist. Most likely are: LHCb (or CDF, Atlas, CMS ?) Super B factories A rather safe estimate for performance can be made by using Babar as basis to project to integrated luminosity of 75 ab-1 at (4S) anticipated for SuperB (Similarly for Belle and Super KEKB) We can also speculate on what “SuperD1” [500 fb-1 at (3770)]might accomplish 1See SuperB white paper:http://arxiv.org/abs/1008.1541 ) Dependence on decay mode would indicate direct CPV? LHC performance not yet established Machines do not yet exist !

  41. WS decays D0 K+-: f unknown, f2=RDCS – measure (xD’2, yD’ ) WS decays D0 K+-0: f unknown, f from decay model – measure (xD’’, yD’’) “Lifetime” diff for D0 h+h-: Measure yCP “Golden” D0 Ksh+h- = 0 - measure (xD, yD) directly, ALSO measures |q/p| and Arg{q/p}BUT Introducesirreducible model uncertainty, IMU BaBar Mixing Measurements .02 0 -.02 yD -0.02 0 0.02 .04 0 -.04 yD -0.03 0 0.03 .015 .010 .005 yD -0.02 0 0.02 .010 .005 0 yD -.006 +.009 xD • xDvs.yD PRL 98,211802 (2007) PRL 103:211801 (2009) PRD 78:011105 (2008) PRD 80:071103 (2009) PRL 105:081803 (2010)

  42. Project BaBar Average to 75ab-1@(4S): 480 fb-1 75 ab-1 Golden channels Min. 2 fits (similar to HFAG fits) Represented by blue contours Unofficial average !! Uncertainties shrink: but are limited by the IMU(biggest effect on xD ) Strong phase measurements from (3770) can greatly reduce this.

  43. DD Threshold Measurements Data from  (3770)DD at charm threshold provide measurement of strong phases such as K. They also provide measured values of  in Dalitz plot bins1 These can be used to significantly reduce uncertainties from the Dalitz plot model used in the golden channel analyses. As basis for projection, we take uncertainties from CLEO-c: N. Lowrey et al, PRD80, 031105 (2009), 0903.4853 Our assumption is that new data from threshold will reduce the uncertainties in model uncertainty IMU: BES III: IMU x 1/3 (Factor 3 improvement) SuperD 500 fb-1 @DD threshold: IMU x 1/10 (Factor 10 improvement) 1Bondar, Poluektov & Vorobiev, Phys. Rev. D82, 034033 (2010)

  44. Two improvements in mixing precision come from threshold data: Value of Strong Phase Measurements • Dalitz plot model uncertainty shrinks • Information on overall strong phase K is added BES III SuperD Uncertainty inxDimproves more than that of yD

  45. CPV Parameters |qD/pD |, M=Arg{q/p} Several strategies: 47 • D0- D0 parameter asymmetries: • az = (z+-z-)/(z++z-) ~ |q|2-|p|2 • where z is x, y, x’, y’, x”, y”, x’2 Decay (|q/p|) (M)0 mode x 100 Global 2 Fit to all modes: §18 § 9 (HFAG - direct CPV allowed) Current World Averages (HFAG): Time-dependent amplitude analysis of Golden channels Semi-leptonic asymmetry aSL = Improve present precision by order of magnitude Also improve distinction between decay modes ~ 5% 1-|q/p|4 1-|q/p|4

  46. What About LHCb (10 fb-1) ? + y LHC Guy + G. WilkinsonP. M. Spradlin CERN-lhcb-2007-049. P. M. Spradlin (2007), Arxiv: 0711.1661. LHCb is running now (and doing well) Wait for next talk by Marco Gersabeck

  47. Summary There is strong evidence for mixing in the D0 meson system in four types of analyses: Measurements of yCP agree well with one another. Measurements of xD and yD, rotated by unknown strong phases, have been made for “WS”hadronic decays to K+- and to K+ - 0. Measurement of xD and yD, from CP self-conjugate Ksh+h- decays BUT there is no evidence for CPV in mixing. More B factory mixing measurements are yet to come, as are results from BES III and LHCb. Measurements of strong phases from BES III (3770) data are eagerly anticipated. If Super B factories can produce luminosities ~ 75 ab-1, it may be possible to see CPV as a few percent in |q/p| = 1 and |ÁM| > 50. ~

  48. Backup Here

  49. Time-Integrated CPV from TeVatron Work in progress – Mark Mattson, ICHEP 2010 • Techniques pioneered by Babar, extended and used by Belle, virtually eliminate major systematic effects: • F-B production asymmetry • Use odd moments • Charge efficiency asymmetry • Use data to calibrate, NOT Monte Carlo • Now used by CDF. Interesting  interestinger …

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