 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

Indirect vs. Direct CP Violation KL~ Kodd + Keven “Direct” in decay process  “Indirect” from asymmetric mixing  /   0 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

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

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

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  1996 + 1997 with better systematics

1997 Reconstructed Mass Distributions (before background subtraction)  ~ 1.6 MeV  ~ 1.5 MeV ( distributions exclude 1997a data used in publication.)

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

1997 Reconstructed Vertex z Distributions

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)

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

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

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.

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.

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 