1. July 2001 Snowmass A New Measurement of  from KTeV Introduction The KTeV Detector  Analysis of 1997 Data Update of Previous Result Conclusions E. Blucher, Chicago The KTeV Collaboration: Arizona, Chicago, Colorado, Elmhurst, Fermilab, Osaka, Rice, Rutgers, UCLA, UCSD, Virginia, Wisconsin

2.  /   0 direct CP violation K L ~ K odd +  K even  “Direct” in decay process “Indirect” from asymmetric mixing  Indirect vs. Direct CP Violation Standard Model Prediction: Re(  ) ~ (0-30)  10 -4

3. KTeV Detector K L +  K S KLKL For E K ~ 70 GeV, K S :  c  ~ 3.5m K L :  c  ~ 2.2 km E832:  E799: rare decays

4. Calorimeter Performance

5. KTeV Datataking First result (PRL 83, 22 (99)) used     from 1996 and     from first 18 days of 1997 E832 run (1997a). Current analysis is based on remaining 1997 data -- ~3  larger sample than first result. 1999  run  1996 + 1997 with better systematics

6. K S  +  

7. rabrab zabzab a b K L    

8. 1997 Reconstructed Mass Distributions (before background subtraction)  ~ 1.6 MeV  ~ 1.5 MeV

9. Backgrounds Misidentified kaon decays –For K  +  - : K L  e, K L  –For K  0  0 : K L  0  0  0 Scattered K  events –From regenerator and final collimator Main classes of background: Background levels (in %)

10. Center-of-energy for K     Events K S  +   distribution used to model scattering background in K    . Improvements in procedure revealed a mistake in the background estimation for the published result:  Re(  ) =  1.7  .

11. E K Dependence of Regenerator Scatters

12. Yield after Background Subtraction Vacuum Beam Reg. Beam K     8,593,988 14,903,532 K  0  0 2,489,537 4,130,392 Raw double ratio: (no acceptance correction) K L “K S ”

13. 1997 Reconstructed Vertex z Distributions

14. 0.1% shift in E scale: ~3 cm shift in vertex; ~1   shift in 

15. Acceptance Detailed Monte Carlo simulation based on measured detector geometry and response. Includes: Accidental overlays Full trigger simulation (L1,L2,L3) For K  0  0 : Geant-based shower library for CsI (showers cover 0.675  0.675 m 2 ) Detail photon veto simulation For K  +  - : Detailed drift chamber simulation Magnetic field map CsI pion shower library High statistics decay modes (e.g., K  e, K  3  0 ) are used to check MC simulation.

16. KTeV 1997* Data / Monte Carlo Comparison * excludes 1997a data used in publication. K L     K L  e

17. KTeV 1997 Data / Monte Carlo Comparison K L     K L      

18. Calorimeter Energy Scale Final energy scale adjustment based on regenerator edge. Energy scale depends on P K. Applying an energy-independent scale shifts Re(  ) by -0.5   compared to nominal method.

19. Check E scale with different modes: K      , K*   K S, hadronic 2   production, K  2  0 Dalitz,  3  0 Cross Checks of Energy Scale

20. Systematic Uncertainties for 1997

21. Calculating  Naively, but regenerator beam is not purely K S.

22. K L - K S Interference Downstream of Regenerator KTeV Preliminary Results:

23. History of K S Lifetime Measurements

24. History of  m Measurements

25. Re(  ) = (19.8  1.7 (stat)  2.3 (syst)  0.6 (MC stat))  10 -4 Re(  ) Result from 1997 Data Set

26. Geometry-only Monte Carlo K L     K L  +   Using acceptance correction from MC with perfect detector resolution (only geometry) shifts Re(  by 12   compared to full MC. Correcting for observed data/MC z slope reduces shift to ~2  .

27. Cross-check using reweighting method Provides check of Monte Carlo method Statistically less significant than Monte Carlo method (  ). Reweight K L decays to reg. beam distribution.

28. Effect of Reweighting on Detector Illuminations

29. KTeV NA48 KTeV and NA48 Beams

30. Reweighting Method Result Based on preliminary study of correlation of systematic errors, difference between standard method and reweighting method is:  Re(  ) = (1.5  2.1 (stat)  3 (syst))  

31. Improvements in  Analysis CsI Calibration Drift Chamber calibration and alignment Neutral backgrounds Apertures Attenuation  m,  S

32. Update of Published Result (96-97a dataset) Re(  ) = (23.2  3.0 (stat)  3.2 (syst)  0.7 (MC stat))  10 -4

33. Re(  ) Cross Checks

34. KTeV Results 1997 (independent from published result) Re(  ) = (19.8  1.7 (stat)  2.3 (syst)  0.6 (MC stat))  10 -4 Updated 1996/1997a Re(  ) = (23.2  3.0 (stat)  3.2 (syst)  0.7 (MC stat))  10 -4 Combined 1996+1997 Result Re(  ) = (20.7  1.5 (stat)  2.4 (syst)  0.5 (MC stat))  10 -4 = (20.7  2.8)  10 -4

35. Measurements of Re(  ) World ave. Re(  ) = (17.2   )    (confidence level = 13%)

36. Re(  ) and Im(  ) from Fermilab Experiments

37. Conclusions KTeV results from 1996+1997 data: Re(  ) = (20.7  1.5 (stat)  2.4 (syst)  0.5 (MC stat))  10 -4 = (20.7  2.8)  10 -4 New measurements of  m,  S,  + , and  New world average: Re(  ) = (17.2   )    Full KTeV data sample (96+97+99) will reduce the statistical error on  to ~ 1  10 -4  significant work will be required to reduce systematic error to similar level Theory improvement needed to take full advantage of this precision.