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A New Measurement of  from KTeV

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

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A New Measurement of  from KTeV

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

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

  3. KTeV Detector KL E832:  E799: rare decays KL + KS KS: c ~ 3.5m KL: c ~ 2.2 km For EK ~ 70 GeV,

  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. KS +

  7. KL a rab b zab

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

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

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

  11. EK Dependence of Regenerator Scatters

  12. Yield after Background Subtraction KL “KS” 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)

  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 m2) • 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 KL KLe * excludes 1997a data used in publication.

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

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

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

  20. Systematic Uncertainties for 1997

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

  22. KL - KS Interference Downstream of Regenerator KTeV Preliminary Results:

  23. History of KS Lifetime Measurements

  24. History of m Measurements

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

  26. Geometry-only Monte Carlo KL+ KL • 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 Reweight KL decays to reg. beam distribution. • Provides check of Monte Carlo method • Statistically less significant than Monte Carlo • method ().

  28. Effect of Reweighting on Detector Illuminations

  29. KTeV and NA48 Beams KTeV NA48

  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.

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