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Radiative kpi2 analysis on the data in the year of 1998

This presentation provides an analysis of the radiative kpi2 data collected in 1998 at KEK & Univ. of Tokyo, including kinematic fit, background estimation, confirmation of consistency between real and UMC data, spectrum fitting, and systematic uncertainties. The measurement of the branching ratio of radiative kpi2 is also discussed.

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Radiative kpi2 analysis on the data in the year of 1998

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  1. Radiative kpi2 analysis on the data in the year of 1998 KEK & Univ. of Tokyo Toshinao Tsunemi toshinao@post.kek.jp A technote is available. http://kaon.kek.jp/~toshinao/rkp2/ This presentation is based on the technote.

  2. Outline • Introduction • 1998 data set • Kinematic fit • Background estimation • Confirm consistency between real and UMC • Spectrum fitting • Systematic uncertainties • Measurement of branching ratio of radiative kpi2(IB+DE)

  3. IB and DE Direct Emission (DE) Inner Bremsstrahlung (IB) Radiative kpi2 IB+DE+INT Magnetic Electric Radiative kpi2 IB+INT+DE Interfere (INT)

  4. Radiative kpi2 amplitude DE IB INT

  5. Definition of W

  6. W spectrum

  7. Data set 1998 • Number of Kaon 1998 3.48£1011 (1.2 times) 1995 2.83£1011

  8. trigger 1998 1995

  9. Trigger acceptanceDE component ’95 DE events arbitrary unit Generation level IB generation level

  10. Comparison on trigger between 1995 and 1998 • 500,000 kaon decay to radiative kpi2 10 MeV<Tpi<95 MeV 55 MeV<Tpi<90 MeV (words in parentheses ) The ratio from 1998 trigger is 1.4(1.2) times as much as 1995.

  11. Understanding energy deficit in target • Hidden energy (UMC & Real) • Energy deposit in edge fiber (UMC & Real) • Saturation effect (UMC) • Energy deposit in dead material (Real)

  12. Hidden energyUMC & REAL Pion cells Kaon cells Number of kaon cells in swath Angle between kaon and pion Mean 1.4 MeV dependence • Number of kaon cells • Angle between kaon and pion cells • cos3d MeV

  13. Energy deposit in edge fiberUMC & REAL E787 standard kofia does not unpack energy dropped in edge fiber Mean 1.4 MeV MeV dependence • Distance in edge fiber • cos3d

  14. Saturation effectUMC Saturation effect based on Berk’s formula is simulated in generating UMC data. Mean 0.56 MeV dependence • Measured energy MeV

  15. Energy deposit in dead materialREAL Fibers in target are wrapped with foil. Effect from energy deposit in the foil is added. Mean 0.99 MeV dependence • Range in target • cos3d MeV

  16. Improved reconstruction • Measurement of dropped energy in Target is improved. UMC E787 standard new Measured – true Energy in target

  17. Kinetic energy resolution Real data kpi2 Mean 108.7 Sigma 3.50 Mean 105.1 Sigma 3.55

  18. Kinetic fit (most primary cut) 6 constraints • Momentum conservation (x,y,z 3 constraints) • Energy conservation • mass p+ • mass p0 p+ p0 g 13 variables • Pion Momentum 1 • Energy of pion and gamma 4 • Azimuthal angle 4 • Dip angle 4 g g g p+ 1 pion and 3 gammas

  19. The power of kinetic fit Gamma energy (MeV) before after DE Gamma energy 3.6 times improved

  20. Resolution improvement on W UMC UMC Sigma 0.02 Sigma 0.04

  21. Number of events • Primary cut is kinematic fit. • Background level is negligible. accept • 27450 events (ppg) remain • after all cuts are imposed. Chisquare probability

  22. Kinfit power of rejection Kinfit is imposed as a final cut Pion momentum Charged track consistency

  23. Lower momentum region Events with lower momentum region includes a lot of kpi3 events. Analysis only on standard region looks good.

  24. Number of events CUTS 1)Kinematic fit 2)Number of gamma cluster is 3 3)Range consistency between UTC and range stack 4)Charged track momentum region from 140 MeV/c to 180 MeV/c (standard region) List of all cuts is available at P33 technote. 27450 events remain after all cuts are imposed.

  25. Background estimation

  26. Accidental hit kinfit

  27. Kpi2 with split gamma W>0.5 event: 0

  28. Split gamma W>0.5 event: 7

  29. Ke3 with radiated gamma W>0.5 event: 2

  30. Fused or missing gamma with kpi3 W>0.5 event: 10

  31. Background level

  32. Background level

  33. W spectrum Real IB(UMC) DE(UMC)

  34. Consistency between real and UMC • Spectrum fitting Real data IB (UMC) 2/n.d.f=10.5/14

  35. Real data IB+DE (UMC) Real data IB+DE (UMC) IB (UMC) Spectrum fitting • Real data is fitted by UMC(IB+DE) • Chisquare/n.d.f = 1.4/6 BR(DE) 55 MeV < Tpi < 90 MeV

  36. real data UMC(IB) Pion momentum shift UMC +0.3 MeV BR(DE) +3.4% UMC -0.3 MeV BR(DE) -2.8%

  37. real data UMC(IB) Gamma position resolution UMC +1.5 cm BR(DE) -8.3% UMC -1.5cm BR(DE) 4.0%

  38. real data UMC(IB) Gamma position UMC +5% BR(DE) +1.5% UMC -5% BR(DE) -10.1%

  39. real data UMC(IB) Visible fraction UMC +2% BR(DE) +4.9% UMC -2% BR(DE) -4.3%

  40. Real data IB+DE (UMC) Real data IB+DE (UMC) IB (UMC) Fitting with another spectrum

  41. small UMC statistics IB sample(UMC) is divided into 3 sub-parts. BR(DE)=3.26£10-6 Maximum deviation from result with full UMC sample is assumed as systematic uncertainty. BR(DE)=3.23£10-6 BR(DE)=3.27£10-6 BR(DE)=3.29£10-6 Uncertainty is 0.9%.

  42. Systematic uncertainties

  43. Absolute measurement of Radiative kpi2 branching ratio

  44. Comparison with previous experiment The result is consistent with that of previous experiments.

  45. The technical note E787-TN394 available now: summary The analysis is finished. Standard region 55 MeV/c < Tpi < 90 MeV/c http://kaon.kek.jp/~toshinao/rkp2/

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