A New Measurement of from KTeV

1
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
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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
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KTeV Detector
KL
E832 ???? E799 rare decays
KL ?KS
KS ??c? 3.5m KL ??c? 2.2 km
For EK 70 GeV,
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Calorimeter Performance
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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

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KS ????
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KL?????
a
rab
b
zab
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1997 Reconstructed Mass Distributions
(before background subtraction)
? 1.6 MeV
? 1.5 MeV
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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

Background levels (in )
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Center-of-energy for K????? Events

• KS???? distribution used to model
  scattering
• background in K ?????.

• Improvements in procedure revealed a mistake
• in the background estimation for the
• published result ?Re(????) ?1.7?????.

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EK Dependence of Regenerator Scatters
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Yield after Background Subtraction
KL KS
Vacuum Beam Reg. Beam K????? 8,593,988
14,903,532 K??0?0 2,489,537
4,130,392
Raw double ratio
(no acceptance correction)
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1997 Reconstructed Vertex z Distributions
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0.1 shift in E scale 3 cm shift in
vertex 1????? shift in ????
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Acceptance

• Detailed Monte Carlo simulation based on
• measured detector geometry and response.
• Includes
• Accidental overlays
• Full trigger simulation (L1,L2,L3)
• For K??0?0
• Geant-based shower library for CsI
• (showers cover 0.675?0.675 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 ?3?0) are used to check MC simulation.

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KTeV 1997 Data / Monte Carlo Comparison
KL?????
KL??e?
excludes 1997a data used in publication.
17
KTeV 1997 Data / Monte Carlo Comparison
KL?????
KL???????
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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.
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Cross Checks of Energy Scale
Check E scale with different modes K???????,
K???KS, hadronic 2?? production, K?2?0 Dalitz,
??3?0
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Systematic Uncertainties for 1997
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Calculating ????
Naively,
but regenerator beam is not purely KS.
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KL - KS Interference Downstream of Regenerator
KTeV Preliminary Results
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History of KS Lifetime Measurements
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History of ?m Measurements
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Re(????) Result from 1997 Data Set
Re(????) (19.8 ? 1.7 (stat) ? 2.3 (syst)
? 0.6 (MC stat)) ? 10-4
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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 ?????.

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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 (??????).

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Effect of Reweighting on Detector Illuminations
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KTeV and NA48 Beams
KTeV
NA48
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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)) ?????
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Improvements in ???? Analysis

• CsI Calibration
• Drift Chamber calibration and alignment
• Neutral backgrounds
• Apertures
• Attenuation
• ?m, ?S

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Update of Published Result (96-97a dataset)
Re(????) (23.2 ? 3.0 (stat) ? 3.2 (syst)
? 0.7 (MC stat)) ? 10-4
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Re(????) Cross Checks
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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 19961997 Result
• Re(????) (20.7 ? 1.5 (stat) ? 2.4 (syst)
• ? 0.5 (MC stat)) ? 10-4
• (20.7 ? 2.8) ? 10-4

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Measurements of Re(????)
World ave. Re(????) (17.2 ? ???) ? ????
(confidence level 13)
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Re(????) and Im(????) from Fermilab Experiments
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Conclusions

• KTeV results from 19961997 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 (969799) 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.