D 0 D 0 bar Mixing and CP Violation at BESIII Kanglin He June 2006, Beijing

2 OutLine D 0 D 0 bar Mixing CKM γ/ ϕ 3 measurements CP violation Dalitz Plot analysis Time-Independent measurements using The Quantum Correlation Analysis (TQCA) Summary

3 D 0 D 0 bar Mixing Flavor eigenstate == mass eigenstate Expected to be very small in Standard Model Sensitive to New Physics x, y =0 in the SU(3) limit Experiments are beginning to probe interesting region of mixing parameter space (x, y ~10 -3 )

4 Mixing in the Standard Model and Beyond Standard Model New Physics Common hadronic final states (real, on-shell) (virtual, off-shell) Loops provide sensitivity new physics via x FSI may enhance both x and y in SM

5 Mixing Parameters Mixing rate Strong phase difference of CF decay and DCS decay, important to measure CP eigenstate lifetime difference CP violation phase CP violation in mixing/decay interference If CP is conserved, ϕ=0, Δ=0, y CP =y CPV in mixing

6 Theoretical Predictions Theoretical predictions are very variable x, y in range of From A. Petrov Charm Physics: Theoretical Review hep-ph/ New Physics Standard Model

7 Mixing in High Energy Experiment flavor tag by D*  π + D 0 fitting the time distribution Wrong-sign semileptonic decays(K (*) ev), measure R mix (E791, FOCUS, BELLE, BaBar, etc) Decay to CP eigenstates(KK), measure y CP (E791, FOCUS, BELLE, BaBar, CLEO, etc) Wrong-sign K π decays, measure x ’ 2 and y ’ (CLEO, FOCUS, Belle, BaBar, etc) Dalitz plot analysis (CLEO, Belle, BaBar, etc)

8 Experimental Situation No evidence of mixing has been reported in the charm sector Hopefully to be found in near future y CP measurements (Close to confirm) PDG06

9 D 0 D 0 bar Mixing at BESIII Charm events at threshold are very clean –Ratio of signal to background is optimum –Lots of systematic uncertainties cancellation while applying double tag method Mixing at threshold –Bad news: no time-dependent information –Good news: Quantum coherence, CP tags –The coherence of two initial D allows simple methods to measure DDbar mixing, strong phase and CP violation –Sophisticated methods combining semileptoinc, CP and hadronic modes provide additional sensitivity

10 D 0 D 0 bar Mixing (Kπ ) D 0 decays as D 0 bar Key Point: Separate Mixing from DCSD

11 Separate Mixing from DCSD D0D0 D0D0 K+π-K+π- DCSD mixing CF Two path to D 0  D 0 bar decay final state: 1. D 0  K + π - (DCSD) 2. D 0  D 0 bar － >K + π - (MIX) In the case of no mixing, (K + π - )(K + π - ) is forbidden by Bose-Einstein statistics D 0  Kπ and D 0 bar  Kπ require L even, but for Ψ(3770) decay, L = 1

12 Challenge to PID BESIII PID system –dE/dx, resolution (6-7)% –Two layer barrel TOF, time resolution ~100ps, ~83% solid angle coverage –1 layer endcap TOF, ~110ps Selection efficiency is >20% with a K/π double mis-identification rate at < level

13 Mixing in double semi-leptonic decays (Kev channel) at BESIII Two missing neutrinos in events Electron PID can suppress background The selection efficiency is similar as the Kπ channel Background level is also negligible while running a small MC data sample (~1% of 20fb -1 ). More detail study is needed.

14 R mix sensitivity at BESIII With 20fb -1 (4-5 years running) Ψ(3770) data sample, we may get –~20,000 right sign Kπ events –~20,000 right sign Kev events –If more electronic channels and muonic channels are applied (need further MC studies), more right sign events will be obtained BESIII will probe R mix <10 -4 in combined K π and semileptonic channels (At least)

15 CP eigenstate Tags CP + –K + K - (3.89X10 -3 ) –π + π - (1.38X10 -3 ) –Ks π 0 π 0 –π 0 π 0 (8.4X10 -4 ) –K S K S (7.1X10 -4 ) –ρ 0 π 0 (3.2x10 -3 ) CP – – K S π 0 (0.012) –K s η (3.9X10 -3 ) –K S η’ (0.0094) –K S ρ 0 (0.0078) –K s ω (0.012) –K S φ (4.7X10 -3 ) In 20fb -1 Ψ (3770) data, we can get > 4.5x10 5 CP+ tags and > 3.6x10 5 CP- tags With large sample of CP tags, we may improve the measurements of strong phase, probe the direct CP, and other mixing parameters Dalitz Analysis K L modes can also be applied partially

16 CKMγ/ ϕ 3 measurement Unitarity Triangle Extract γ/ ϕ 3 from B  DK decays, where D decays to 1.D to CP eigenstates (GLW): improved constraints on charm mixing amplitude 2.D to flavor eigenstates K π (ADS): measurement of relative rate and strong phase 3.D to Ksππ(Dalitz plot analysis): studies of charm Dalitz plots tagged by flavor or CP eigenstates Need help from charm sector

17 Asymmetry =  K+K+ K+K+  CP+ eigenstate  K+K+ KSKS  CP- eigenstate  K+K+ K+K+  CP+ eigenstate  K+K+ KSKS  CP- eigenstate Useful for probing r &  = 2 r cos  Strong Phase (I) If CPV=0 Mixing is small Ratio of DSCD/CF

18 Strong Phase (II) In 20fb -1 Ψ (3770) data, we can get > 10,000 CP+ vs Kπ double tags > 10,000 CP- vs Kπ double tags The precision of cos δ < 0.06 level is expected at BESIII, Be helpful to improve the precision of γ/ ϕ 3 measurement

19 CP Violation 1. Direct CP Violation (in decay) 2. Indirect CP Violation (in mixing) 3. CP violation in the interference between decays with/without mixing

20 CP violation in Charm decays In SM, no Direct CP asymmetry in CF and DCS modes. New physics Buccella et al. predict CP asymmetries in decay in the range of 0.002%  0.14%, may up to level Indirect CPV due to mixing is a possibility for D 0 decays CP studies in charm transitions represent an almost 0-background search for New Physics (Bigi and Sanda) If New Physics intervenes through DCSD, then it would have the cleanest impact on D +  K S,L π+ (Bigi and Sanda)

21 Direct CP Violation Need two paths (CKM  weak +FSI  strong) from initial D to final state f D f D f Compare D  f to D  f Find: Singly Cabbibo Suppressed decays (SCSD) should be the good choice to measure a sizeable asymmertry Not too diff.

22 Experimental search CP Violation in Charm decays A Cabbibo allowed reference states is needed to calibrate the known production/detection asymmetries Define Where η is the ratio of N (searched) / N (referenced) D 0 : K - π +, D + : K - π + π +, Ds: K - K + π + D 0 : K - K +, π - π +, Ks π 0, etc D + : K - K + π +, Ks π +, KsK +, etc Ds: KsK +, Ks π +, etc DCSD mode: D +  K + π + π - D 0  K + π - π - π + Probe New Physics

23 CP asymmetry measurement 1% level reached for some decay modes, no evidence of CP Violation ExperimentDecay modeA CP (%)comments BaBar D+K-K+π+D+K-K+π+ 1.4±1.0±0.8 D+ϕπ+D+ϕπ+ 0.2±1.5±0.6 Resonant substruct of D +  K - K + π + D +  K *0 K + 0.9±1.7±0.7 CLEOD0π+π-π0D0π+π-π ±8Dalitz Analysis CDF D0K-K+D0K-K+ 2.0±1.2±0.6 Direct CPV D0π-π+D0π-π+ 1.0±1.3±0.6 FOCUS D0K-K+π+π-D0K-K+π+π- 1.0±5.7±3.7 T Violation through triple product correlations D+K0K+π+π-D+K0K+π+π- 2.3±6.2±2.2 Ds  K 0 K + π + π ±6.7±2.3

24 CP Violation at BESIII Quantum Coherence –Psi(3770) --  D(CP+)D(CP+), D(CP-)D(CP-) CP asymmetry in D + and Ds decays –Lots of modes, include DCSD CP asymmetry in D 0 decays –Have to pay price for tag –Flavor tag with semileptonic mode at Ψ(3770) –Flavor tag with D -  K + π - π - modes above DD* threshold (4.03GeV / 4.17 GeV) Indirect CP asymmetry is too hard to BESIII

25 Quantum Coherence Suppose Both D 0 decay to CP eigenstate f 1 and f 2. Thus if a final state such as (KK)( ππ ) observed, we immediately have evidence of CP violation In 20 fb -1 Ψ (3770) data, > 1000 double CP+ and CP- tags can be obtained. if 100%CPV, it lead to A CP ~10 -3 level

26 CP Violation in Charm decays (I) D+K-K+π+D+K-K+π+ ~3x10 5 D +  Ksπ + ~5x10 5 D +  KsK + ~1x10 5 Ds  K + π + π - ~10 5 D 0  K + π - /K + π - π - π + 300/500(DT) D+K+π+π-D+K+π+π- ~3x10 4 In 20fb -1 data, BESIII can obtain the precision of CP asymmetry in decays of charmed mesons for the DCSD modes, BESIII can probe New Physics at A CP ~(10 -2  ) level

27 CP Violation in Charm decays (II) XsecExpD* + D - + D* - D + D* + D* GeVBES I2.31nb0.87nb 4.14GeVMark III0.7nb1.8nb If 20fb -1 data taking at 4.03GeV, ~9,000 D 0 CP tags 4.17GeV, ~5,000 D 0 CP tags Expected to be obtained Flavor tagged by D -  K + π - π - The precision of CP asymmetry will be

28 CPV interference with Mixing Two interesting case with semileptonic tag + CP tags CPV in Mixing is small, Δ=0 In 20fb-1 psi(3770) data,  10,000 SL+CP(+) tags  10,000 SL+CP(-) tags Δy CP and ΔA Γ ~ 1% level Applying the inclusive semileptonic tag Can improve the measurements

29 Dalitz Plot Analysis Developed by CLEO, BaBar, Belle, etc Modes: Ksπ + π -, K - π + π 0, K - K + π +, π - π + π 0, etc Time-dependent Mixing measurements DCSD branching ratio measurement (including phase) CP Violation studies Measurements of γ/ ϕ 3 in B  D (*) K (*) Strong phase measurement The powerful tool will be applied in BESIII What will we do next? 1.Understanding the ππ or Kπ S-wave scattering (learn from BESII J/Psi analysis and other experiments, such as: applying K-matrix formulism etc) 2. Currently, we have a piece of FORTRAN code. Develop a OO version PWA package for charm decays in future

30 CPV in Dalitz Analysis Strong phase, do not change sign under CP conjugation CPV phase, change sign under CP conjugation Phase difference hints that CP is violated CP asymmetry across Dalitz plots Advantage of using Dalitz plot Analysis: 1.Measure CP asymmetries 2.Direct access to the phase

31 Dalitz Analysis at BESIII Interesting topic (I) K - π + π 0, Ksπ + π - vs CP tags, measure strong phase of Kρ, K*π K - π + π 0, Ksπ + π - vs flavor tags, measure Br of DCSD Ksπ + π -, π - π + π 0 vs CP tags, search for CP Violation (via same sign CP Tags) CP asymmetries across Dalitz Plots –Ksπ + π -, π - π + π 0 vs flavor tags –D +  K - K + π +

32 Dalitz Analysis at BESIII Interesting topic (II) Simultaneously fit two Dalitz plots of K - π + π 0 vs K - π + π 0 and Ksπ + π - vs Ksπ + π -, search for Mixing in Kρ, K*π modes PWA analysis to D  VV vs CP Tags, search for CP violation and measure the strong phase more and more, …… Lots of interesting modes can be applied, to improve the measurements of Mixing parameters and search for CP violations in charm decays Key point: Quantum Coherence

33 Time-independent Quantum Coherence The Quantum Coherence Analysis (TQCA) Ψ(3770)  D 0 D 0 bar C=-1 Ψ(4040)/Ψ(4160)  (mγ)(n π 0 ) D 0 D 0 bar C=(- 1) m+1 measure R M, r, cosδ K π, y and xsinδ K π (at Ψ(4040) or Ψ(4160)) Suggested by D. Asner and Sun etc, part of CLEO-c physics program Will be applied at BES III

34 TQCA at psi(3770) fl+l+ CP+CP- f RMRM l+l+ r2r2 RMRM l-l- 111 CP+ 1+2rcosδ10 CP- 1-2rcosδ120 X 1+2yrcosδ11-y1+y DT ST R M = (x 2 +y 2 )/2 r = Amp DCS/Amp CF See PRD (2006) [hep-ph/ ] by Asner and Sun Measure RM, r, cosδ K π and decay fractions

35 TQCA (C=+1) fl+l+ CP+CP- f 4r(r+ycosδ-xsinδ) l+l+ r(r+2(ycosδ-xsinδ))3R M l-l- 1+2r(ycosδ+xsinδ)1 CP+ 1-2rcosδ-2y1-2y2(1-2y) CP- 1+2rcosδ+2y1+2y02(1+2y) X 1+2yrcosδ11-y1+y DT ST Have a chance to measure y and xsinδ K π

36 Estimated uncertainties (stat.) of Mixing parameters using TQCA parametervalue CLEO-c (3x10 6 D 0 D 0 b)BESIII(20fb-1) C=-1C=+1C=-1C=+1 y0±0.015±0.007±0.003±0.002 x2x2 0±0.0006±0.0003± ± cosδ K π 1±0.15±0.13±0.035±0.04 xsinδ K π 0 ─ ±0.010 ─ ±0.003 From PRD (2006) by Asner and Sun Scale to BESIII Have to identify C=+1 of γD 0 D 0 bar and γ D 0 D 0 barπ 0 from D*Dbar and D*D*bar decays

37 Summary Mixing parameters –R mix < in Kπ and Kev channels –Δcos δ Kπ < 0.05 –Probe y: y CP ~ 10 -4, Δy CP ~ 1%, Probe x: 4.03/4.17 GeV –Possible to probe CPV phase ϕ if x is sizeable CP Violation –ΔA CP ~10 -3 in D+ decays, –Probe new physics at A CP <10 -2 level in DCSD –Probe A CP <10 -3 level with DT CP tags Dalitz Plot Analysis are expected to improve the measurements TQCA method can improve the measurements A lot of work need to do in future Excited results can be produced at BESIII in Mixing and CP Violation in Charm sector!!!

Thank You !