D0 Mixing and CP Violation from Belle Eric White U. of Cincinnati CHARM 2010, Oct. 21-24 IHEP Beijing, China Eric White – University of Cincinnati 1/18/2019

Introduction Review of Charm Mixing and CP Violation Formalism Charm Mixing Results (WS, time-dep., …) CP Violation in Time-integrated Decays (KSh±, KSP0, … ) Conclusion Eric White – University of Cincinnati 1/18/2019

KEKB and Belle Detector Largest integrated luminosity in the world, ~1020 fb-1 Electron-positron beam, proceeds through: e+e- → Υ(4S) → bb e+e- → γ → cc σ(bb) = 1.1 nb σ(cc) = 1.3 nb ~1.3 x 109 cc pairs B-factories serve as good charm factories! _ _ _ _ _ Eric White – University of Cincinnati 1/18/2019

Mixing Formalism Mixing often expressed in terms of mass and width differences of eigenstates: _ Evolution of D0-D0 system described by time-dependent Schrodinger equation and mixing parameters: _ Mixing occurs when flavor eigenstates (D0, D0) produced in decays are not the same as mass eigenstates (D1, D2). Time-dependent expression for D0 decay rate is given by: Eric White – University of Cincinnati 1/18/2019

Contributions to x and y Standard Model predictions for x and y Contributions from SU(3) breaking and hadronic intermediate states give: x, y < 10-2 Mixing strongly suppressed in charmed mesons by CKM and GIM mechanism, calculable short-distance effects give: Difficult to calculate, BUT measurements of x and y can still provide useful constraints on New Physics models |x|, |y| < 10-5 Birdman, Shipsey, Ann.Rev.Nucl.Part.Sci.53,431 Golowich,Hewett,Pakvasa,Petrov arXiv:0705.3650v2 Eric White – University of Cincinnati 1/18/2019

Common experimental observables CP Violation in Charm CP violation arises as a single complex phase η in the CKM mixing matrix CP violation in SM is CKM suppressed, ~O(10-3) Observation of O(1%) CP violation would be a sign for New Physics CP-violating effects are classified by three parameters: 1) CP violation in decay: 2) CP violation in mixing: 3) CP violation in interference: Common experimental observables Eric White – University of Cincinnati 1/18/2019

Decays to CP Eigenstates In terms of mixing parameters: Limit no CP violation, yCP = y and AΓ = 0 Eric White – University of Cincinnati 1/18/2019

Reconstructing D Mesons Tagging the flavor of neutral D meson Proper decay time determination Reconstruct decay chain: D*+  D0 π+ Beam point is used to constrain vertex fit: Flavor of D0 is tagged by slow pion Background suppression using mass difference D mesons from b  c are eliminated with pD*cms > 2.5 GeV/c2 Uncertainty t typically between 1/6D and 1/2D Eric White – University of Cincinnati 1/18/2019

D-Mixing in D0 → K+K-, π+π- Proper decay time was fitted for each sample [540 fb-1, ~130K K+K- events, ~57K π+π- events] Staric et al. (Belle), PRL98, 211803 (2007) + = yCP = (1.31 ± 0.32 ± 0.25)% Measured to 3.2σ significance, first evidence of mixing AΓ = (0.01 ± 0.30 ± 0.15)% No CPV observed to .4% sensitivity Eric White – University of Cincinnati 1/18/2019

D-Mixing in D0 → KSK+K- yCP = (0.11 ± 0.61 ± 0.52)% Measure lifetime differences between CP-even and CP-odd eigenstates Zupanc et al. (Belle), Phys.Rev.D80:052006 (2009) fON and fOFF regions fit with 8-resonance Dalitz model 72K signal events in ON region, 62K in OFF yCP = (0.11 ± 0.61 ± 0.52)% Purity: 97% Purity: 91% Consistent with previous measurement of yCP Eric White – University of Cincinnati 1/18/2019

Mixing in WS Decay D0 → K+π- WS rate include DCS, interference, and mixing RD = DCS/CF rate x' = x cosδ + y sinδ y' = y cosδ – x sinδ (δ = strong phase) Eric White – University of Cincinnati 1/18/2019

Mixing in WS Decay D0 → K+π- Belle [400 fb-1] Zhang et al. (Belle), Phys.Rev.Lett.96, 151801 (2006) _ D0 and D0 samples fit separately: y‘ = (0.6+4.0-3.9)10-3 x’2 = (0.18+.21-.23)10-3 No-mixing point (0,0) corresponds to C.L. 3.9% Eric White – University of Cincinnati 1/18/2019

Mixing in Time-dependent Dalitz Analyses Dalitz plots provide unique environment for determining strong phases between D0 and D0 decays in self-conjugate final states. Contributions include: _ _ CF: D0 → K*-π+ DCS: D0 → K*+π- CP: D0 → KSρ0 Decay model is parameterized using Dalitz variables The time-dep. decay rate allows simultaneous determination of x and y Eric White – University of Cincinnati 1/18/2019

Mixing in Time-dependent D0→KSπ+π- Zhang et al. Phys.Rev.Lett.99:131803 (2007) Belle [540 fb-1] Allowing for CPV Assuming no CP violation: No CP violation observed Eric White – University of Cincinnati 1/18/2019

CP Violation in Time-integrated Decays Standard Model predicts O(0.1%) direct CP violation in Singly Cabibbo-Suppressed (SCS) decays Grossman et al. arXiv:hep-ph/0609178v1 Examples: D+→KSπ+, D+→KSK+ Must distinguish possible CP asymmetry from reconstruction asymmetries, such as detector effects and production asymmetry Includes (-0.332 ± 0.006)% CP violation due to neutral kaon ACP = CP asymmetry, independent of kinematics AFB = Production asymmetry, due to γ*/Z interference Aε = Reconstruction efficiency asymmetry (plab, cosθlab) Deviations in ACP greater than 0.1% could signify New Physics Eric White – University of Cincinnati 1/18/2019

CP Violation in D+→KSπ+ Ko et al. (2010), PRL 104, 181602 673 fb-1 Measured in bins of (plab, cosθlab, cosθD*CMS) 1) For D+→KSπ+ measure Arec = AFB + Aε+ + ACP 2) For DS+→π+ measure Arec = AFB + Aε+ 3) Subtract measured asymmetries ACP(D+→KSπ+) = (-0.71 ± 0.19 ± 0.20)% Results consistent with -0.33% due to neutral kaon Eric White – University of Cincinnati 1/18/2019

CP Violation in D(s)+→KSK+ Ko et al. (2010), PRL 104, 181602 673 fb-1 ACP(D+→KSK+) = (-0.16 ± 0.58 ± 0.25)% ACP(DS+→KSK+) = (0.12 ± 0.36 ± 0.22)% Consistent with -0.33% due to neutral kaon Most precise measurement of SCS/CF: R(D+) = 0.1899  0.0011  0.0022 R(DS+) = 0.0803  0.0024  0.0019 673 fb-1 Dashed line: leading-order prediction for AFB Eric White – University of Cincinnati 1/18/2019

Results consistent with -0.33% due to neutral kaon CP Violation in D0→KSP0 PRELIMINARY Events reconstructed from tagged D* sample 791 fb-1 ACP(D0→KSπ0) = (-0.28 ± 0.19 ± 0.10)% ACP(D0→KSη) = (-0.54 ± 0.51 ± 0.13)%* ACP(D0→KSη’) = (-0.90 ± 0.67 ± 0.15)%* *World’s first measurement Results consistent with -0.33% due to neutral kaon Eric White – University of Cincinnati 1/18/2019

ΔACP between D+→φπ+ and Ds+→φπ+ PRELIMINARY Event reconstruction as follows: ΔACP defined as ACP(D+→φπ+) - ACP(Ds+→φπ+) 850 fb-1 ΔACP = (0.62 ± 0.30 ± 0.15)% No significant difference found in production asymmetry of D+ and Ds+ Eric White – University of Cincinnati 1/18/2019

Prospects with Belle’s Full Data Set Belle now has about ~1 ab-1 for mixing measurements Updating previous mixing analyses and working on new measurements Expect significant improvement in sensitivity to mixing and CP violation Additionally, expect 20-40% increase in signal yields due to new reprocessing E.g. signal yield for D0→KSπ+π- analysis increased from 534K events to ~1.25M Eric White – University of Cincinnati 1/18/2019

Conclusion Wide program of D-mixing and CP violation underway at Belle Measurements have provided compelling evidence for D0-D0 mixing No evidence of CP violation to 0.3% level of sensitivity First ACP measure measurements for D0→KSη and D0→KSη’ Expect significant improvement with full dataset, new analyses underway Best D-mixing and CP violation measurements to come? Eric White – University of Cincinnati 1/18/2019

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