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KTeV Results: K L  p 0 ll ( l =e, m , n )

KTeV Results: K L  p 0 ll ( l =e, m , n ). BEACH 2004 June 30, 2004 Julie Whitmore, Fermilab Physics Motivation - Direct CP Violation KTeV Detector Results Summary The KTeV Collaboration: Arizona, Campinas, Chicago, Colorado, Elmhurst, Fermilab, Osaka,

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KTeV Results: K L  p 0 ll ( l =e, m , n )

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  1. KTeV Results: KL p0ll(l=e,m,n) BEACH 2004 June 30, 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

  2. Direct CP Violation in KLp0ll DIR Direct (KL K2 + e K1;K2 p0g*,p0Z*) The Golden Mode

  3. CP Violation in KLp0ll (from theory + BR(Ksp0ll) (NA48)) 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 Theoretical Predictions (from theory + BR(KLp0gg))

  4. 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

  5. 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)

  6. KLp0nn Muon Counters Muon Steel CsI g e+ n n KL e- from e+e- Z vertex • 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 – Dalitz Trigger Prescaled

  7. KLp0nn Data MC BG Sum Lnp0MC XLp0 MC Signal MC BR(KL p0nn)  5.9 x 10-7 (0ee, 1997 Data)[PRD 61,072006 (2000)] BR (KLp0nn)  1.6 x 10-6 (0g, 1997 1 Day) [PLB 447, 240 (1999)] 1997 Data Dalitz Analysis

  8. KL p0e+e- • Advantage: fully reconstruct the final state. • Disadvantages: not pure direct CP violation Serious background (KL eegg) • Contributions to BR(KL p0e+e-) • CP Violating: BR ~ (17 ± 9 + 5) x 10-12 (est. from theory+KS p0e+e-) • CP Conserving: BR ~ 0.5 x 10-12 (est. from theory+ KL p0gg) • Total:BR (KL p0e+e-)= (1-3) x 10-11 • New Physics  Enhancements in BR Previous Result: BR (KL p0e+e- )< 5.1 x 10-10 (KTeV1997) [PRL 86, 397 (2001)]

  9. KL e+e-gg KL 00,0eeg KLeeg +gACC 1988 Events 76.6  3.3 Est. Background BR(KL  e+e-gg, Eg*>5MeV) = (6.310.14(stat)±0.42(sys))x10-7[PRD 64, 012003 (2001)]

  10. KL p0e+e- Muon Counters Muon Steel CsI g e+ g KL e- from e+e- Z vertex • Analysis – 1999 Data • Event selection: 2 g forming p0; 2 electron-like showers matched to tracks, CsI+TRD(p/e) • Backgrounds: KL p0+-, KL en+gacc+grad, and KL eegg • Suppress with kinematic Cuts: |COS(p)| and min • Total contribution in the blind analysis box: 3.9 ± 1.4 events (2.9 ± 0.47 events come fromKL eegg) • Normalize to KL p0p0,p0 eeg

  11. KL  p0e+e- KLp0 p0 p0 eX eX gg KLe +p0ACC KLe+rad + gACC KL p0 p0 p0 egX eX gX KL eegg; Mgg Mp0 Blind Analysis Box Region Signal Ellipse ±2s Mgg Mp0

  12. Kinematic Variables for KL  p0e+e- and KL  e+e-gg KLeegg KLp0ee min Cos() KLp0e+e- KLe+e-gg KLp0ee KLeegg

  13. Kinematic Cuts for KL  p0e+e- and KL  e+e-gg Cos (Qp) QMIN • 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)<0.745 QMIN>0.362

  14. KL  p0e+e- 1999 Data Box Region: 130<mgg<140 MeV/c2 485<meegg<510 MeV/c2 Signal Region: ±2s in KLp0e+e- Background in ellipse: 0.99 ±0.35 BR(KL  p0e+e-)  3.50 x 10-10 (90% C.L.) (1999) [Accepted by PRL] BR(KL p0e+e-)  2.8 x 10-10 (90% C.L.) (1997+1999)

  15. KL p0+m- • Advantage: Probes direct CP violation Like KL p0e+e- - 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 p0m+m-) • CP Violating: BR ~ (9 ± 6 + 1) x 10-12(est. from theory + KS p0m+m-) • CP Conserving: BR ~ 5 x 10-12 (est. from theory+ KL p0gg) • Total:BR (KL p0m+m-)= (1 – 2) x 10-11 • New Physics  Enhancements in BR Previous limit: BR (KL p0m+m- )< 5.1 x 10-9 (E799-I)

  16. KL p0+m- Muon Counters Muon Steel CsI g m+ g KL m- Z vertex from m+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 p+p-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 p+p-p0 decays

  17. KL m+m-gg • Dangerous background for KL p0m+m- • 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), mmg+gACC • Kinematic Cuts: Eg • Total Contribution: 0.155 ± 0.081 • Normalize to KL +-0 • QED Pred:BR(KL m+m-gg) = (9.1 0.78) x 10-9

  18. KL mmgg BR(KL m+m-gg,Mgg>1MeV/c2) = BR(KL m+m-gg, Eg*>10MeV) = 4 events seen First observation [PRD 62, 112001 (2000)]

  19. Kinematic Distributions for KL p0+m- and KL +m-gg Cos() min KLp0mm KLmmgg KLp0mm KLmmgg KLp0mm KLmmgg

  20. KL p0mm  BR(KL p0mm)  3.8 x 10-10 (90% C.L.) [PRL 86, 5425 (2001)] 2 events in signal region Data Background MC

  21. Current Status

  22. Summary • Analyzed 1997 data - BR(KLp0nn)  5.9 x 10-7 (0ee) • B(KL  e+e-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 p0e+e-) 2.8 x 10-10 (90% C.L.) • Analyzed 1997 data - BR(KL p0mm)  3.8 x 10-10 (90% C.L.) • B(KL m+m-gg) = (1.42 (+1.0-0.08)  0.10)x 10-9 • Currently analyzing 1999 data • Combined 1997+1999 data set ~ 2 x 1997 • More accidentals – tighter cuts (lose acceptance) • Normalize to KL m+m-g – reduce uncertainties from muon system • Expected SES (1997+1999) ~ 1 x 10-10

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