 Results from KTeV

1.  Results from KTeV E. Blucher, Chicago • Introduction • The KTeV Detector • Status of  analysis • Conclusions The KTeV Collaboration: Arizona, Chicago, Colorado, Elmhurst, Fermilab, Osaka, Rice, Rutgers, UCLA, UCSD, Virginia, Wisconsin ICHEP 2000, Osaka

2. Indirect vs. Direct CP Violation KL~ Kodd + Keven  “Indirect” from asymmetric mixing “Direct” in decay process  /   0 direct CP violation KTeV Goal: measure /  to 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. KTeV CsI Electromagnetic Calorimeter KL a rab b zab

5. KTeV Datataking K for first result K+- for first result ,+- for this analysis • First result 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. 1997 Reconstructed Mass Distributions (before background subtraction)  ~ 1.6 MeV  ~ 1.5 MeV ( distributions exclude 1997a data used in publication.)

7. 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 K00 events

8. 1997 Reconstructed Vertex z Distributions

9. Acceptance • Acceptance correction based on detailed Monte Carlo simulation. • High statistics decay modes (e.g., K e, K 30) are used to check MC simulation. • Largest systematic error in first result came from data/MC comparison of z distributions for K +: 1997a K + Data / MC Comparison from first result + Data/MC z slope:  = 1.6 Total syst. error from K+:  = 2.0 Total systematic error:  = 2.8 (from first result)

10. KTeV 1997* Data / Monte Carlo Comparison (preliminary) KL KLe * excludes 1997a data used in publication.

11. KTeV 1997 Data / Monte Carlo Comparison (preliminary) KL KL

12. Status of  Analysis of 1997 Data • K: ~ complete; all systematics have been evaluated (current  sys. error ~ 2/3  sys. error in first result). Work to reduce systematic error is continuing. • K : completing systematic studies. The 1997 analysis has been done blind. Thevalue of  is still hidden.

13. Stability of Vacuum Beam (KL) / Regenerator Beam (“KS”) Ratio for  KTeV preliminary  1104 97a 97b Run periods in 1997b rest of 1997 data published data (statistical errors only) • 1997b K data are consistent with • 1997a K data used in published result. • K ratioand are still hidden.

14. Conclusions • Published KTeV result: Re() = (28.0  3.0 (stat)  2.8(syst))  10-4 = (28.0  4.1)  10-4 • Analysis of remaining 1997 sample is almost complete. Statistical error on this independent data sample will be 1.7 10-4 • Full KTeV data sample (96+97+99) will reduce the statistical error on  to ~ 1  10-4   may be measured to 5%! • KTeV data sample will also provide precise measurements of m, S, +, 00, , and 