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July 2001 Snowmass
A New Measurement of from KTeV
• Introduction• The KTeV Detector Analysis of 1997 Data• Update of Previous Result• Conclusions
E. Blucher, Chicago
The KTeV Collaboration: Arizona, Chicago, Colorado, Elmhurst, Fermilab, Osaka, Rice, Rutgers, UCLA, UCSD, Virginia, Wisconsin
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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
Standard Model Prediction: Re() ~ (0-30)10-4
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KTeV Detector
KL + KS
KL
For EK ~ 70 GeV, KS: c ~ 3.5mKL: c ~ 2.2 km
E832: E799: rare decays
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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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rab
zab
a
b
0
22
2a b ab
ab
E E rz
m
KL
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1997 Reconstructed Mass Distributions(before background subtraction)
~1.6 MeV
~1.5 MeV
Vacuum beam (KL) Reg. Beam ("KS") 00 + 00 )stat
(106) (106) (106) (106) (10-4)1996 2.6 0.9 4.5 1.4 3.01997 8.6 2.5 14.9 4.1 1.796+97 11.2 3.4 19.4 5.6 1.5
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Backgrounds
• Misidentified kaon decays– For K+-: KLe, KL
– For K00: KL000
• Scattered K events– From regenerator and final collimator
Main classes of background:
Vac
Reg
Vac00
Reg00
Misidentified K: Kl 0.090 0.003 K
0.11 ~0Scattered K: regenerator 0.073 0.25 1.13 collimator 0.010 0.010 0.12 0.09Total 0.100 0.087 0.48 1.23
Background levels (in %)
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Center-of-energy for K Events
• KS+ distribution used to model scattering background in K .
2tp
• 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
Vacuum Beam Reg. Beam
K 8,593,988 14,903,532
K00 2,489,537 4,130,392
Raw double ratio:
8593988 /149035320.96
2489537 / 4130392R
(no acceptance correction)
KL “KS”
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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 K00:
Geant-based shower library for CsI (showers cover 0.6750.675 m2)Detail photon veto simulation
• For K+-:Detailed drift chamber simulationMagnetic field mapCsI pion shower library
High statistics decay modes (e.g., K e,K 30) are used to check MC simulation.
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KTeV 1997* Data / Monte Carlo Comparison
* excludes 1997a data used in publication.
KL KLe
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KTeV 1997 Data / Monte Carlo Comparison
KL KL
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Calorimeter Energy Scale
Final energy scaleadjustment based on regenerator edge.
Energy scale depends on PK.
Applying an energy-independentscale shifts Re() by -0.5 compared to nominal method.
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Check E scale with different modes:K, K*KS,hadronic 2 production,K20 Dalitz, 30
Cross Checks of Energy Scale
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Systematic Uncertainties for 1997
Uncertainty in (10
)Source of uncertainty
from
from
0.62
0.16--
0.280.250.20
0.330.150.370.53
0.16
1.370.660.380.371.06
0.480.08
--0.26
Data collection: Trigger (L1/L2/L3)Event recon., backgrounds: Energy scale Calorimeter nonlinearity Detector calibration alignment Analysis cut variations Background subtractionDetector acceptance: Limiting apertures Detector resolution Drift chamber simulation Z dependence of acceptanceKaon flux, physics parameters: Reg-beam attenuation m, s
Regeneration phase, screening
0.190.240.31
TOTAL 2.32
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Calculating
0 0 0 0
0 0 0 0
N(Vac ) N(Reg )/
1 Acc(Vac ) Acc(Reg )Re( / ) 1 ,
N(Vac ) N(Reg )6/
Acc(Vac ) Acc(Reg )
Naively,
but regenerator beam is not purely KS.
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KL - KS Interference Downstream of Regenerator
KTeV Preliminary Results: 6 1
14
00
(5262 7.7(exp) 13(ext)) 10
(8967.1 3.5(exp) 4(ext)) 10
44.11 0.72 (stat) 1.1 (syst)
0.41 0.22 (stat) 0.53 (syst)
S
m s
s
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History of KS Lifetime Measurements
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History of m Measurements
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Re() = (19.8 1.7 (stat) 2.3 (syst) 0.6 (MC stat)) 10-4
Re() Result from 1997 Data Set
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Geometry-only Monte Carlo
KLKL+
• 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
• Provides check of Monte Carlo method• Statistically less significant than Monte Carlo method ().
Reweight KL decays to reg. beam distribution.
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Effect of Reweighting on Detector Illuminations
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KTeV
NA48
KTeV and NA48 Beams
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Reweighting Method Result
Based on preliminary study of correlation ofsystematic 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 1996+1997 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 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.