1.  Results from KTeV Introduction The KTeV Detector
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
July 2000
ICHEP 2000, Osaka

2. Indirect vs. Direct CP Violation
KL~ Kodd + Keven
“Direct”
in decay
process 
“Indirect” from
asymmetric
mixing 
/   direct CP violation
to distinguish betwen direct CP violation in the decay amplitude and indirect CP violation arising from asymmetric kkbar oscillations, we compare the level of CP violation in the charged and neutral 2pi decays. If the ratio of CP violating to cp conserving decays is different for charged and neutral decays, that signals direct CP violation and results in e'/e different from zero.
KTeV Goal: measure /  to 10-4

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

4. KTeV CsI Electromagnetic Calorimeter
The CsI calorimeter is the key component of the experiment. It is 2m square and is made of 3100 pure CsI crystals. It has excellent position and energy resolution; the average energy resolution for photons from 2pi0 events is 0.7%.You can see the two beam holes where the neutral beams pass through the detector.
The event display shows a 2pi0 event in the calorimeter. Since
we do not measure photon direction, we use the pi0 mass as
a constraint to caluclate the decay position using the energies
and positions of the photons. This connection between photon energy and z is why the calorimeter is so critical to the experiment.
KL a
rab b
zab

5. KTeV Datataking First result used  from 1996 and 
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  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. Main classes of background: Misidentified kaon decays
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.
The value 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 ratio and  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 ( ) 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 