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Search for D 0 D 0 Mixing and Direct CP Violation in 2-body Hadronic Decays

Search for D 0 D 0 Mixing and Direct CP Violation in 2-body Hadronic Decays. Y.Z. Sun, J.Y. Zhang IHEP Mar. 08, 2006. Outline. D 0 D 0 Mixing In SM, Mixing is very small (10 -6 ) BESIII is sensitive to 10 -4 Direct CP Violation SM predicts the A cp may be as big as 10 -3

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Search for D 0 D 0 Mixing and Direct CP Violation in 2-body Hadronic Decays

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  1. Search for D0D0 Mixing and Direct CP Violation in 2-body Hadronic Decays Y.Z. Sun, J.Y. Zhang IHEP Mar. 08, 2006

  2. Outline • D0D0 Mixing • In SM, Mixing is very small (10-6) • BESIII is sensitive to 10-4 • Direct CP Violation • SM predicts the Acp may be as big as 10-3 • BESIII is sensitive up to 10-2 • Experimental search at Ψ(3770) • Challenge to detector and Accelerator performance • Good place to look for new physics • Summary

  3. D0D0 Mixing D0 decays as D0 Key Point: Separate Mixing from DCSD

  4. Mixing Phenomenology(1) D0,D0 not mass eigenstates but flavor eigenstates Two eigenstates D01 and D02: their masses M1, M2 and widths Γ1, Γ2 Like the K0K0 mixing, constructing DS and DL

  5. Mixing Phenomenology(2) Mixing Measuring the Asymmetry of CP eigen state (K+K-(+), Ksρ0(-)…) DCS CF Supposing CP violation is small Possible to measure the phase shift

  6. 0.1 y 0 -0.1 0 0.2 0.1 x Experimental Situation x and y are in the orders of 10-1─10-2

  7. Separate Mixing from DCSD Two path to D0D0 decay final state: D0－>K+π- (DCSD) D0－>D0－>K+π- (MIX) DCSD impossible : D0Kπ and D0Kπ require L even For Ψ(3770) decay, L = 1 mixing D0 DCSD D0 K+π- CF

  8. Experimental Approach • 2-body hadronic channel • Kπ vs Kπ • Big challenge to PID • Quasi 2-body hadronic channel • K-ρ+ vs K-ρ+, K*-π+ vsK*-π+, K*0 π0 vs K*0 π0 • D0K-π+ π0 Dalitz Analysis (Both D together) • Sensitivity need detail study • Semi-leptonic channel • Klν vs Klv, l= e,μ • Hard to reduce background Kπ channel is selected in this analysis

  9. Analysis Technique • Main background source • KK, π π channel • Double miss identification: K π, πK • Kinematic information • P distribution • ΔEdistribution • Kinematic Fit • Particle Identification • Barrel TOF pid

  10. ΔE Distribution π misidentified as K K, π double misidentified K misidentified as π D0Kπsample

  11. Big Challenge to PID(I) Learn from ΔE distribution • Background from KK,ππ can be removed easily • ΔE CUT can not totally remove the background due to double mis-PID D0Kπ D0 π π D0KK PK Pπ

  12. Big Challenge to PID(II) K,π momentum distributes between 0.65-1.05 GeV • dE/dx is hard to separate • Barrel TOF has best K/π separation at BESIII R>0.9 • R>0.9 cut: • Lost ~20% eff • Remove >99%bg R

  13. Results • Events pass ΔE cut and PID cut are subjected to 5C kinematicfit with additional equal mass constraint • ~12.5% efficiency and ~1 background event from 100K Monte Carlo sample Normal tag Mixing tag ~1 background event is expected Efficiency:12.5% MKπ(GeV)

  14. Direct CP Violation at ψ(3770) Suppose Both D0 decay to CP eigenstate f1 and f2 . Thus if a final state such as (KK)(ππ) observed, we immediately have evidence of CP violation

  15. CP + K+K- (3.89X10-3 ) π+π- (1.38X10-3 ) ρ0 π0 (<0.011) π 0π0 (8.4X10-4) KSKS (7.1X10-4) CP – KSπ0(0.023) Ksη (7.7X10-3) KSρ0 (0.0155) Ksω (0.024) KSφ (9.4X10-3) KSη’ (0.0188) CP eigen states D0 K+K-, π+π- are selected to search for Direct CP Violation

  16. KK vs KK and ππ vs ππ mode Same procedure as Mixing analysis 100K D0(KK, ππ) vs D0(KK, ππ)Monte Carlo sample KK and ππ are mixed according to BF MKK Mππ

  17. KK vs ππ Mode • Contamination due to the cross talk from Kπ vs Kπ mode • Additional cuts on χ2(KKππ)<χ2(KπKπ) χ2(KKππ)-χ2(KπKπ) MD Kπ vs Kπ KK vs ππ Analysis maybe need improving

  18. Summary • Data sample • 15fb-1  5.8x107 D0D0 pair • D0D0 Mixing • 1~2 background events leads to • rD < (3-4)x10-4 @ 90%C.L. • Direct CP Violation • ~120 events will be expected in KK vs KK and ππ vs ππ modes if CP is violated completely • ~100 events will be expected in KK vs ππ mode if CP is violated completely • ACP < 10-2 @90% C.L. • Further plan • Study other interesting channels • Apply new analysis technique Analysis based on BOSS 5.0.0, results may be updated in future

  19. THANK YOU

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