July 2000 ICHEP 2000, Osaka

Results from KTeV

• Introduction• The KTeV Detector• Status of analysis• Conclusions

E. Blucher, Chicago

The KTeV Collaboration: Arizona, Chicago, Colorado, Elmhurst, Fermilab, Osaka, Rice, Rutgers, UCLA, UCSD, Virginia, Wisconsin

1

/

/61

/Re0000

sL

sL

KK

KK

/ 0 direct CP violation

KL~ Kodd + Keven

“Direct”in decayprocess

“Indirect” from asymmetric mixing

Indirect vs. Direct CP Violation

00K K

KTeV Goal: measure / to 10-4

KTeV Detector

KL + KS

KL

For EK ~ 70 GeV, KS: c ~ 3.5mKL: c ~ 2.2 km

E832: E799: rare decays

KTeV CsI Electromagnetic Calorimeter

rab

zab

a

b

0

22

2a b ab

ab

E E rz

m

KL

KTeV Datataking

,+-

for thisanalysis

Kfor firstresult

K+-

for firstresult

• 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

1997 Reconstructed Mass Distributions(before background subtraction)

( distributions exclude 1997a data used in publication.)

~1.6 MeV

~1.5 MeV

Backgrounds

• Misidentified kaon decays– For K+-: KLe, KL

– For K00: KL000

• Scattered K events– From regenerator and final collimator

Main classes of background:

K00 events

1997 Reconstructed Vertex z Distributions

Acceptance

• Acceptance correction based on detailed Monte Carlo simulation.

• High statistics decay modes (e.g., K e,

K 30) 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)

KTeV 1997* Data / Monte Carlo Comparison(preliminary)

* excludes 1997a data used in publication.

KL KLe

KL KL

KTeV 1997 Data / Monte Carlo Comparison(preliminary)

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 doneblind. The value of is still hidden.

Stability of Vacuum Beam (KL) / Regenerator Beam (“KS”) Ratio for

• 1997b K data are consistent with 1997a K data used in published result.

• K ratio and are still hidden.

Run periods in 1997b

publ

ishe

d da

ta

rest

of

1997

dat

a

97a 97b 1104

KTeV preliminary

(statistical errors only)

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