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A New Measurement of Re( e ’ /e) from KTeV at Fermilab

A New Measurement of Re( e ’ /e) from KTeV at Fermilab. Introduction to CP Violation in the Kaon System The KTeV Experiment at Fermilab Analysis of Re( e ’ /e) New 1997 Result, and Re-analysis of 1996 Result. are quark flavor eigenstates

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A New Measurement of Re( e ’ /e) from KTeV at Fermilab

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  1. A New Measurement of Re(e’/e) from KTeV at Fermilab • Introduction to CP Violation in the Kaon System • The KTeV Experiment at Fermilab • Analysis of Re(e’/e) • New 1997 Result, and Re-analysis of 1996 Result P. Shanahan – FNAL SLAC - July 26, 2001

  2. are quark flavor eigenstates Mixing via ElectroWeak interaction: In CP conserving limit, mass eigenstates=CP eigenstates: Expect K1 to be much shorted lived than K2, since MK-3Mp0<< MK-2Mp0 The Neutral Kaon System P. Shanahan – FNAL SLAC - July 26, 2001

  3. CP Violation in Kaons • 1st Observation of CP Violation was KLpp (1964): • Bulk of effect is from mixing asymmetry: • Mass Eigenstates: KSK1+eK2, KLeK1+K2 tL580 tS, Dm1/2tS P. Shanahan – FNAL SLAC - July 26, 2001

  4. CP Violation in the Standard Model • CP Violation is accommodated in imaginary part of quark mixing parameters: P. Shanahan – FNAL SLAC - July 26, 2001

  5. KL  e K1 + K2 e Direct (decay) Indirect (mixing) p p d d Direct CP Violation • Direct CP Violation: • CP Violation in Decay Amplitudes: EW and Stong Penguins • Small effect on CP violating KL Amplitudes: W d s q u,c,t Z,g q P. Shanahan – FNAL SLAC - July 26, 2001

  6. e’/e in the Standard Model • e’Im(A2/A0) : A0,2– I=0,2 Final State • e’/e =Im(lt) x [ c0 + Rs(c6B6(1/2)+c8B8(3/2))] • c0,6,8 – Wilson Coefficients, NLO (~ 10%) • Im(lt) – Im(VtdVts*) (~ 40%) • B6,8(1/2) – Hadronic matrix elements of effective 4 quark operators – non perturbative, difficult to calculate. • e’/e calculations vary… (4.63.0)x10-4 -Ciuchini, et al. 97 (5.73.6)x10-4 -ms=130 20 MeV (9.15.7)x10-4 -ms=110 20 MeV (17 )x10-4 -Bertolino, et al., 98 Buras, et al., 99 { +14 -10 P. Shanahan – FNAL SLAC - July 26, 2001

  7. Previous Measurements • Pre-June, 2001: World Average e’/e=(18.02.0)x10-4, poor agreement among experiments. P. Shanahan – FNAL SLAC - July 26, 2001

  8. KTeV at Fermilab • Kaons at the TeVatron • Three Physics Programs: • Rare K decays: E799 • Hyperon Physics: E799/E832 • e’/e: E832 • d(e’/e)=O(10-4) University of Arizona, UCLA ,UCSD, Universidade Estadual de Campinas, University of Chicago, University of Colorado, Elmhurst College, Fermilab, Osaka University, Rice University, Universidade de São Paulo, University of Virginia, University of Wisconsin P. Shanahan – FNAL SLAC - July 26, 2001

  9. Measuring e’/e • Simultaneous KL and KS beams: 20-200 GeV • Produce 2 KL beams 160 m upstream of the detector • Coherent regeneration of KS in 1.8m of plastic scintillator 35 m upstream of detector • Detector • Spectrometer for p+p- • CsI EM Calorimeter for p0p04g KL (VAC Beam) KL KL+rKS (REG Beam) Regenerator switches beam every spill P. Shanahan – FNAL SLAC - July 26, 2001

  10. KTeV Detector P. Shanahan – FNAL SLAC - July 26, 2001

  11. Coherent Regeneration • Difference in K0 and K0 forward scattering amplitude in matter • r0.02-0.04, with power law dependence in PK • Coherent effect • Distinguish from inelastic KS production via scintillation light from recoil in interactions • Subtract diffractive and remaining inelastic and background offline Inelastic Coherent P. Shanahan – FNAL SLAC - July 26, 2001

  12. P. Shanahan – FNAL SLAC - July 26, 2001

  13. Cesium Iodide Calorimeter • 3100 Crystals of 27 X0 Pure CsI (50cm) • High Linearity Phototubes • 8 Range, Deadtimeless, Pipelined ADC 1.9m P. Shanahan – FNAL SLAC - July 26, 2001

  14. P. Shanahan – FNAL SLAC - July 26, 2001

  15. CsI Performance • CsI Calibrated with e from 420 Million Kpen Energy Resolution P. Shanahan – FNAL SLAC - July 26, 2001

  16. KTeV Trigger P. Shanahan – FNAL SLAC - July 26, 2001

  17. e/e Standard Analysis • Count KL,S to p+p-and p0p0 • Background Subtraction – non pp and non-coherent Kpp • Very different KL and KS lifetimes: • Need acceptance correction from Monte Carlo simulation of detector + overlay of accidental activity • Fit for e’/e • Account for full kaon wave function in each beam P. Shanahan – FNAL SLAC - July 26, 2001

  18. KTeV Data Taking 1996 1997 1999 2000 E799 E832 1st KTeV result, and re-analysis New result P. Shanahan – FNAL SLAC - July 26, 2001

  19. Event Sample P. Shanahan – FNAL SLAC - July 26, 2001

  20. Reconstructed Invariant Masses P. Shanahan – FNAL SLAC - July 26, 2001

  21. p+p Reconstruction • 2 good tracks, forming a good vertex • Cuts PT2 Track Quality Vertex 2 Muon Veto reject Kpmn E/p reject Kpen “pp” Mass reject Lpp Regenerator Veto noncoherent KS PT2nocoherent KS, non pp Regenerator mpp E Zvtx P. Shanahan – FNAL SLAC - July 26, 2001

  22. Interference in Kpp P. Shanahan – FNAL SLAC - July 26, 2001

  23. Backgrounds to p+p- • Non-coherent KS regeneration • Scattering in regenerator • Scattering in collimators • Kpln • Beam interactions in REG Pb Total: .098% VAC .081% REG P. Shanahan – FNAL SLAC - July 26, 2001

  24. Monte Carlo Simulation • Detector apertures/ performance • Overlay real random activity • E.g.: Delayed hit problem • Worst for tracks near Drift Chamber sense wires P. Shanahan – FNAL SLAC - July 26, 2001

  25. Simulation Results P. Shanahan – FNAL SLAC - July 26, 2001

  26. Acceptance Data-MC comparison of p track illumination at CsI MC tuned with 10s of millions of CP conserving decays P. Shanahan – FNAL SLAC - July 26, 2001

  27. Acceptance Test • Comparison of Data and MC Z vertex Distributions • Test of acceptance in variable most relevant to KL-KS difference • Set systematic uncertainty based on p+p-: • d(e’/e)=0.53x10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  28. p0p0 Reconstruction • Vertex for each pair of photons found assuming p0 mass • Choose pairing with most consistent p0 vertices • Calculate p0p0 mass • No direction information – use energy centroids Good pairing Bad pairing Cuts: Photon Veto 3p0 Cluster Shape 2“Fused” gs (3p0) Vertex Pairing c2 Mispairs, 3p0 Regenerator Activity Non-coherents (X,Y)CE Non-coherents Mp0p0, EK, Zvtx Extra intime photons in CsI 3p0 P. Shanahan – FNAL SLAC - July 26, 2001

  29. p0p0 Center of Energy • Cut on center of energy • In 1 cm2 square rings • Simulate Regenerator scattering spectrum using pt2 shape from p+p- P. Shanahan – FNAL SLAC - July 26, 2001

  30. Backgrounds to p0p0 • Dominant BG: Regenerator Scatters • Modeled from Kp+p-pT2 Spectrum • Separate normalization of diffractive and inelastic KS production REG Beam: 1.27% VAC Beam: 0.50% P. Shanahan – FNAL SLAC - July 26, 2001

  31. Energy Scale • Energy Scale: • Apply correction (1+d)-1 • Relative Data-MC energy scale correction: Make data and MC regenerator edge line up. P. Shanahan – FNAL SLAC - July 26, 2001

  32. Energy Scale Cross Check • Beam interactions • Regenerator Pb • Vacuum window • Kp+p-p0 • For systematic: • Apply extra energy scale, varying linearly from Regenerator, to fix ZVACWIN • d(e’/e)=1.37x10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  33. Acceptance Test • Set systematic uncertainty from 3p0 • d(e’/e)=0.26x10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  34. Systematic Uncertainties P. Shanahan – FNAL SLAC - July 26, 2001

  35. KTeV 1997 e’/e Result Re(e’/e)=(19.81.7(stat) 2.3(syst) 0.6(mc stat))x10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  36. Reweighting Analysis • MC acceptance correction is only ~5% on the double ratio • … but this is ~90x10-4 on e’/e • We have strong cross checks on our acceptance calculation • E.g., purely geometrical MC accounts for about 90% of the acceptance correction • However, an “MC independent” measurement is desirable: • Reweighting: • reweight VAC beam to have same p,Z distribution as REG • Similar to NA48 method (CERN), but more complicated due to substantial interference of KL and KS P. Shanahan – FNAL SLAC - July 26, 2001

  37. Pros and Cons of Reweighting • Reweighting completely removes biases from lifetimes and geometry • Reweighting de-emphasizes tracks near beam regions • Less susceptibility to rate and accidental effects • Statistically weaker • -d(e’/e): 1.7x10-43.0x10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  38. Examples of Reweighting Data vs. Data P. Shanahan – FNAL SLAC - July 26, 2001

  39. Reweighting Result • Preliminary reweighting results (NOT the official KTeV Number….) • Re(e’/e)=21.32.9(stat) 4.0(syst) • Hope to reduce systematic… With preliminary understanding of correlated uncertainties, D(e’/e)=(1.5 2.1(stat) 3 (syst) ) x10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  40. Other Cross Checks P. Shanahan – FNAL SLAC - July 26, 2001

  41. Re-Analysis of 1996/97a Result • Miscellaneous improvements • e.g. recalibration, Mask Anti, DC Simulation • Mistake found in p0p0 scattering background • External parameters • Dm, tS from KTeV (was PDG98) P. Shanahan – FNAL SLAC - July 26, 2001

  42. Updated 1996/97a Results New 1996 Result: e’/e=(23.2  3.0 (stat)  3.2 (syst)  0.7 (MC st))x10-4 Old Result: (superceded) e’/e=(28.0  3.0 (stat)  2.7 (syst)  1.0 (MC st))x10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  43. Shifts in Updated Analysis Each consistent With quoted Systematic uncertainty P. Shanahan – FNAL SLAC - July 26, 2001

  44. Combined 1996 and 1997 Results Re(e’/e)=(20.7 1.5(stat) 2.4(syst) 0.5(MC Stat) )x10-4 Re(e’/e)=( 20.7  2.8 ) x 10-4 P. Shanahan – FNAL SLAC - July 26, 2001

  45. World Data on Re(e’/e) • World Average: • (17.21.8)x10-4 • Probability=13% P. Shanahan – FNAL SLAC - July 26, 2001

  46. Kaon System Parameters KS, KL, and Interference in REG Beam allows measurement Of several Kaon system parameters P. Shanahan – FNAL SLAC - July 26, 2001

  47. P. Shanahan – FNAL SLAC - July 26, 2001

  48. Conclusions • KTeV has new Re(e’/e) result with improved error • Re-analysis of 1996 result • Combined KTeV Result: • Re(e’/e)=(20.72.8)x10-4 • World data now in significantly better agreement • World Average: (17.21.8)x10-4 • 13% CL • e’/e now known to ~10% • More data from 1999 run! P. Shanahan – FNAL SLAC - July 26, 2001

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