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
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
KTeV Detector KL E832: E799: rare decays KL + KS KS: c ~ 3.5m KL: c ~ 2.2 km For EK ~ 70 GeV,
Calorimeter Performance
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
KS +
KL a rab b zab
(before background subtraction) 1997 Reconstructed Mass Distributions ~ 1.6 MeV ~ 1.5 MeV
Backgrounds Main classes of background: • Misidentified kaon decays • For K+-: KLe, KL • For K00: KL000 • Scattered K events • From regenerator and final collimator Background levels (in %)
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.
EK Dependence of Regenerator Scatters
Yield after Background Subtraction KL “KS” Vacuum Beam Reg. Beam K 8,593,988 14,903,532 K00 2,489,537 4,130,392 Raw double ratio: (no acceptance correction)
1997 Reconstructed Vertex z Distributions
0.1% shift in E scale: ~3 cm shift in vertex; ~1 shift in
Acceptance • Detailed Monte Carlo simulation based on • measured detector geometry and response. • Includes: • Accidental overlays • Full trigger simulation (L1,L2,L3) • For K00: • Geant-based shower library for CsI • (showers cover 0.6750.675 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 30) are used to check MC simulation.
KTeV 1997* Data / Monte Carlo Comparison KL KLe * excludes 1997a data used in publication.
KTeV 1997 Data / Monte Carlo Comparison KL KL
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.
Cross Checks of Energy Scale Check E scale with different modes: K, K*KS, hadronic 2 production, K20 Dalitz, 30
Systematic Uncertainties for 1997
Calculating Naively, but regenerator beam is not purely KS.
KL - KS Interference Downstream of Regenerator KTeV Preliminary Results:
History of KS Lifetime Measurements
History of m Measurements
Re() Result from 1997 Data Set Re() = (19.8 1.7 (stat) 2.3 (syst) 0.6 (MC stat)) 10-4
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 .
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 ().
Effect of Reweighting on Detector Illuminations
KTeV and NA48 Beams KTeV NA48
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))
Improvements in Analysis • CsI Calibration • Drift Chamber calibration and alignment • Neutral backgrounds • Apertures • Attenuation • m, S
Update of Published Result(96-97a dataset) Re() = (23.2 3.0 (stat) 3.2 (syst) 0.7 (MC stat)) 10-4
Re() Cross Checks
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
Measurements of Re() World ave. Re()= (17.2 ) (confidence level = 13%)
Re() and Im() from Fermilab Experiments
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.
