KTeV Results: KL p0 ll le,m,n

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KTeV Results KL ? p0 ll (le,m,n)

• Brookhaven Workshop on Future Kaon Experiments
• May 13, 2004
• Julie Whitmore, Fermilab
• Physics Motivation - Direct CP Violation
• KTeV Detector
• Results
• Summary
• The KTeV Collaboration
• Arizona, Campinas, Chicago, Colorado, Elmhurst,
  Fermilab, Osaka,
• Rice, Rutgers, Sao Paulo, UCLA, UCSD, Virginia,
  Wisconsin
• 
  

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Direct CP Violation in KL ? p0 ll

• 
  

• Direct (KL ?K2 e K1 K2 ? p0g,p0Z)

Theoretical Predictions
The Golden Mode
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CP Violation in KL ? p0 ll

• 
  

CPV Indirect (KL ?K2 e K1 K1 ? p0g,p0Z)
Interference Direct (KL ?K2 e K1 K2 ?
p0g,p0Z) Conserving(KL ?K2 e K1 K2 ?
p0g g)



Theoretical Predictions
(from theory BR(Ks?p0ll) (NA48))
Theoretical Predictions
(from theory BR(Ks?p0gg))
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KTeV Fixed Target Run

• KTeV(E832) 96-97 Data Set 3.3E6 KL ?p0p0
• KTeV (E799-II) 97 Data Set 2.7E11 KL Decays
• KTeV(E832) 99 Data Set 3.7E6 KL ?p0p0
• KTeV (E799-II) 99 Data Set 3.6E11 KL Decays

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The KTeV Detector

• Pure CsI Calorimeter
• (Energy resolution ? 1 at ?Eg ? 10GeV,
  p/e rejection of ? 700)
• Transition radiation detectors (p/e rejection of
  ? 200)
• Drift chambers with resolutions (100?m)
• Clean intense beams (5-8)E12 protons on target
  per spill
• 5-8 x 109 kaons per spill
• KTeV (E799-II) Data Set
• 6.3E11 Kaon Decays (97 99)

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KL ? p0nn

• Advantage - Dominated by direct CP violation
• Disadvantage - ?0 ? gg difficult Dalitz decay
  BR(?0 ? eeg ) significant backgrounds
• 1997 Analyses
• Dalitz Analysis (?0 ? eeg )
• Event Selection 1 g , 2 electron-like showers
  matched to tracks, unbalanced Pt
• Backgrounds KL ? 2?0 , KL ? 3?0, ? ? n?0, ? ?
  ??0
• Normalize to KL ? eeg
• Neutral Analysis (?0 ? gg )
• Special Run - 1 Day of data taking, Single
  smaller beam
• Normalize to (KL??0 ?0 )
• 1999 Data No Dalitz Trigger

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KL ? p0nn
1997 Data Dalitz Analysis
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KL ? p0ee-

• Advantage fully reconstruct the final state.
• Disadvantages not pure direct CP violation
• Serious background (KL
  ? eegg)
• Contributions to BR(KL ? p0ee-)
• CP Violating BR (17 9 5) x 10-12 (est.
  from theoryKS ? p0ee-)
• CP Conserving BR 0.5 x 10-12 (est. from
  theory KL ? p0gg)
• TotalBR (KL ? p0ee- ) (1-3) x 10-11
• New Physics ? Enhancements in BR
• Previous Result BR (KL ? p0ee- )lt 5.1 x 10-10
  (KTeV1997) PRL 86, 397 (2001)

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KL ? ee-gg
1988 Events 76.6 ? 3.3 Est. Background
BR(KL ? ee-gg, Eggt5MeV) (6.31?0.14(stat)0.42
(sys))x10-7 PRD 64, 012003 (2001)
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KL ? p0ee-

• Analysis 1999 Data
• Event selection 2 g forming p0 2
  electron-like showers matched to tracks,
  CsITRD(p/e)
• Backgrounds KL ? p0??-, KL ? ?engaccgrad, and
  KL ? eegg
• Suppress with kinematic Cuts COS(?p) and ?min
• Total contribution in the box 3.9 1.4 events
  (2.9 0.47 events come from KL ? eegg)
• Normalize to KL ? p0 p0,p0 ?eeg

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KL ? p0ee-
KL? eegg Mgg? Mp0
Signal Ellipse
Mgg? Mp0
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Kinematic Variables for KL ? p0ee- and KL ?
ee-gg

KL?p0ee
KL?eegg
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Kinematic Cuts for KL ? p0ee- and KL ? ee-gg

• Phase space cuts optimized
• Cuts varied and expected background and signal
  acceptance calculated
• 90 CL BR limit determined for each set via
  Feldman-Cousins technique
• Assume any events are background
• Cuts optimized to yield lowest expected branching
  ratio limit
• Signal Acceptance (2.749 0.013)
• 30 less than 1997 due to accidentals (tighter
  TRD, phase space, and mass cuts)
• SES 1.04 x 10-10

Cos(Qp)lt0.745
QMINgt0.362
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KL ? p0ee-
1999 Data Box Region 130ltmgglt140
MeV/c2 485ltmeegglt510 MeV/c2 Signal Region 2s
in KL?p0ee- Background in ellipse 0.99 0.35
BR(KL ? p0ee-) ? 3.50 x 10-10 (90 C.L.)
(1999) Submitted to PRL BR(KL ? p0ee-) ? 2.8
x 10-10 (90 C.L.) (19971999)
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KL ? p0?m-

• Advantage Probes direct CP violation
• Like KL ? p0ee- - fully reconstruct the final
  state
• Disadvantages phase space suppression
• Small relative to the CPC and Indirect CPV
• Potential background (KL ? mmgg)
• Contributions to BR(KL ? p0mm-)
• CP Violating BR (9 6 1) x 10-12(est. from
  theory KS ? p0mm-)
• CP Conserving BR 5 x 10-12 (est. from theory
  KL ? p0gg)
• TotalBR (KL ? p0mm- ) (1 2) x 10-11
• New Physics ? Enhancements in BR
• Previous limit BR (KL ? p0mm- )lt 5.1 x 10-9
  (E799-I)

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KL ? p0?m-

• 1997 Analysis
• Event Selection 2 g reconstructing as a p0 2
  tracks which MIP in the calorimeter, 2 ID muons
• Backgrounds from p punch-through and p
  decay-in-flight from pp-p0 and KL?pmn ( 2?ACC)
  
• KL ? mmgg (0.373 ? 0.032 evts)
• Suppress with kinematic cuts on M(gg) and M(mm)
• Angular cuts on COS(?p) and ?min less
  effective than with eegg
• Total contribution 0.87 0.15 events
• Normalize to pp-p0 decays

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KL ? mm-gg

• Dangerous background for KL ? p0mm-
• Never been observed
• Analysis
• Event Selection 2 g which do not reconstruct
  as a p0
• 2 tracks which MIP in the calorimeter,
  2 ID muons
• Backgrounds from KL ? pmn(2?ACC), mmggACC
• Kinematic Cuts Eg
• Total Contribution 0.155 0.081
• Normalize to KL ? ??-?0
• QED PredBR(KL ? mm-gg) (9.1 ? 0.78) x 10-9

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KL ? mmgg

4 events seen
First observation
PRD 62, 112001 (2000)
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Kinematic Distributions for KL ? p0?m- and KL ?
?m-gg
KL?mmgg
KL?p0mm
KL?p0mm
KL?mmgg
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KL ? p0mm

2 events in signal region
Data
Background MC
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Summary

• Analyzed 1997 data - BR(KL ? p0nn) ? 5.9 x 10-7
  (?0?ee?)
• B(KL ? ee-gg) (6.31 ? 0.14(stat) ?
  0.42(sys))x10-7
• No Dalitz trigger in1999 data
• Look forward to future experiments KOPIO and
  E391a
• Analyzed full KTeV data set (1997 1999) -
  BR(KL ? p0ee-) ? 2.8 x 10-10 (90 C.L.)
• Analyzed 1997 data - BR(KL ? p0mm) ? 3.8 x 10-10
  (90 C.L.)
• B(KL ? mm-gg) (1.42 (1.0-0.08) ? 0.10)x 10-9
• Currently analyzing 1999 data
• Combined 19971999 data set 2 x 1997
• More accidentals tighter cuts (lose acceptance)
  
• Normalize to KL ? mm-g reduce uncertainties
  from muon system
• Expected SES (19971999) 1 x 10-10