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CHARM MIXING and lifetimes

CHARM MIXING and lifetimes. at. Alexis POMPILI. Università and I.N.F.N. Bari. on behalf of the BaBar Collaboration XXXVIIth Rencontres de Moriond - March 11th, 2002. Search for lifetime differences in D 0 decays New BaBar limits on D 0 mixing parameter y :

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CHARM MIXING and lifetimes

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  1. CHARM MIXINGand lifetimes at Alexis POMPILI Università and I.N.F.N. Bari on behalf of the BaBar Collaboration XXXVIIth Rencontres de Moriond-March 11th, 2002 Search for lifetime differences in D0 decays New BaBar limits on D0 mixing parameter y: - method and event selection - lifetime extraction, systematics and results

  2. INTRODUCTION:x, y (flavour eigenstates) Mass eigenstates: masses: M1 , M2&widths: G1 , G2 MIXING PARAMETERS: New Physics can significantly enhancex In the SM : …but … FSI and SU(3) breaking can enhance y Current sensitivy @ level of 10-2 (few 10-3 with 0.5ab –1 @ Belle & BaBar ) HADRONIC 3 types of experiments are sensitive to a combination of x & y : Wrong-sign searches : Semileptonic LIFETIME DIFFERENCE searches 2 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  3. Lifetime difference search strategy Rate asymmetry for neutral D decays into CP+(even) and CP- (odd) eigenstates : K-K+ (p-p+) is CP+ eigenstate & K-p+assumed an equal mixture of CP+, CP- Extracting the rates by fitting to pure exp. the time-dependent rates: NO CP CP in interference mixing-decay CP in mixing 3 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  4. D0 proper time reconstruction method Reconstructed DECAY CHAIN TAG 3 independent samples D*is primary vertex : use BS -constraint 1) allows flavor-tagging dm = m(h+h-ps) - m(h+h-) 2) reduces BKG Refitting technique with BS - constraint improvesdm resolution tDinxy Beamspot DECAY LENGTH 4 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  5. D0 candidates selection criteria This analysis uses 57.8 fb-1 (2000+2001 data) & selects events from continuum It uses alsosimulated (G4) data : Tracking [DCH+SVT], vertexing[SVT], PID [DIRC+(DCH+SVT)] are crucial GOOD QUALITY TRACKS & VERTEXING RESOLUTION (at least6 SVT-hits forps) GOOD VERTEX FITfor BOTH D0 and D* vertices : REJECTION of D* from B decays: ONLY PARTICLE IDENTIFICATION applied on BOTH D0 DAUGHTERS K : tight likelihood selection ( pion contamination: <3% for p<3GeV/c ) p : likelihood selection & muon veto REJECTION of combinatorial BKG due to low p pions : helicity-cut on dm-cut : 5 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  6. m(h+h-) dm=m(h+h-ps)-m(h+h-) Selected D0 candidates after dm-cut K-p+ K-K+ K-p+ p-p+ K-p+ 6 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  7. Unbinned maximum likelihood fit S1 S2 s3 tD (1-f2)(1-f3) + f2(1-f3) + f3 Psig(mi) SIGNAL proper-time RESOLUTION tBKG e BUT with ... SBKG S1 + f0(1-f4) (1-f0) SBKG S2 NO-flying BKG [1-Psig(mi)] flying BKG s3 s4 fixed BKG f0f4 for tails 7 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  8. D0 candidate signal probabilityin the lifetime fit “sidebands”candidates as part of likelihood fit BKG constrained in data K-p+ LOW MASS TAIL K-p+ Portion assigned to BKG K-p+ K-K+ p-p+ 8 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  9. Proper time distributions and lifetime fit results p-p+ K-p+ K-K+ Points : DATA|White histogram : FIT RESULT|Gray histogram : BKG fit portion 9 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  10. Lifetime ratio systematics -I D0 lifetime measurement is an HIGH PRECISION measurement [ statistical uncertainty for our data sample is about 1.3fs namely 3/1000 ] At this level of precision wide studies of systematics sources (tracking, vertexing, alignment) are needed. Note: - 1.5mm average bias in vertex position translates in 3fs lifetime bias - 1MeV mass shift due to momentum bias means 0.3fs lifetime bias At this stage we do not present an absolute D0 lifetime value becausethe overall systematic uncertainty (about 3-4fs) can be reduced with further work We checked, on a limited sub-sample, the full compatibility of the fit result with both our HF2001 check and PDG value Many systematics effects on lifetime cancel in the lifetime RATIO 10 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  11. Lifetime ratio systematics -II y systematics uncertainties calculated using large signal MC samples • Simulated data has been modified by variation reflectinguncertainties in… • detector biases • event selection criteria • size and composition of BKG contribution • - beamspot position and size SVT internal alignment systematic checks done using [zero lifetime control sample] MC estimation shows about null bias within its statistical error which is taken as a fur- ther systematic uncertainty 11 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  12. RESULTS: limitsony PRELIMINARY EPS-2001 12 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  13. CONCLUSIONS AND NEAR TERM PROSPECTS Our preliminary y measurement is consistent with zerobut suggest a positive value not incompatible with FOCUS measurement It is crucial to get a new measurement over LARGER DATA SAMPLES It is important to get a result from D*-untagged KK sample : the statistical uncertainty is <1% but still working on systematics Limits on x, y from hadronic wrong-sign analysis coming soon ! 13 Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  14. BACKUP TRANSPARENCIES (NOT SHOWN)

  15. Wrong-sign hadronic search strategy Type of experiment sensitive to (xcosd + ysind) cosf , (ycosd -xsind) sinf , x2 +y2 x’ y’ • : strongphase diff.between DCSD & CF Look for deviation from exp in the time evolution of neutral D wrong-sign decay : D*+ D0(cu) p+ NO CP DCSD INTERFERENCE MIXING DCSD MIXING HF9 CFD D0 K+p- 1+ Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  16. Kaon ID performance < Efficiency > < Mis-ID > 2+ Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  17. Low mass tail MC study: possible explanation is internal bremsstrahlung Simulation by randomly selecting 5% of D0 candidates for which one daughter’s momentum is correctedby the factor [1-(Eg/mD)] where energy Eg is properly randomly generated. 3+ Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

  18. MC check : lifetime pull The resolution model is found to fit reasonably well to the MC MC indicates very little or null bias (meas. – true) pr. time /pr. time error (measured – true) proper time 4+ Alexis Pompili(Univ. & INFN Bari)XXXVIIth Rencontres de Moriond

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