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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,

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## A New Measurement of from KTeV

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**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,**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**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.**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)**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**Calculating **Naively, but regenerator beam is not purely KS.**KL - KS Interference Downstream of Regenerator**KTeV Preliminary Results:**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 ().**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**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.

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