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Updates on BR(K +  π + π 0 ) E. De Lucia

Updates on BR(K +  π + π 0 ) E. De Lucia. The starting point. PDG fit ‘06 BR(K ±  p ± p 0 ) = (20,92 ± 0.12)% D BR/BR = 5,7x10 -3 CHIANG ’72 BR(K ±  p ± p 0 ) = (21,18 ± 0.28)% D BR/BR = 1,3x10 -2 N.B. This decay enters in the normalization of BR(K  l3) by NA48, ISTRA+, E865.

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Updates on BR(K +  π + π 0 ) E. De Lucia

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  1. Updates on BR(K+π+π0)E. De Lucia Neutral and Charged Kaon Meeting – 7 May 2007

  2. The starting point PDG fit ‘06 BR(K±p±p0) = (20,92 ± 0.12)% DBR/BR = 5,7x10-3 CHIANG ’72 BR(K±p±p0) = (21,18 ± 0.28)%DBR/BR = 1,3x10-2 N.B. This decay enters in the normalization of BR(Kl3) by NA48, ISTRA+, E865 Method: • Self-triggering K-m-n tag • Fitting the distribution of the momentum of the charged decay particle in the kaon rest frame assuming the pion mass (p*) • Global efficiencyeTRK+VTX from K±X±p0 decay vertex technique: • asymmetric p*(p0) cut (old method) • ~12% correction from mc_method/mc_true + 11% Kl3 contamination • d_fromClu cut (new method) • ~1% correction from mc_method/mc_true + 3% Kl3 contamination • The shape for the pp0 peak: old vs new method • investigating on the results obtained Neutral and Charged Kaon Meeting – 7 May 2007

  3. Signal selection • tag on one side with K • preselection • -zPCA  20cm • - rPCA  10cm • - pK (70,130) MeV • selection • - rVTX  (40,150) cm • - dp  (-320,-120) MeV • - p(mp)  (180,270) MeV • self-triggering tag • (2 trigger sectors fired) • 2) look for signal on the other side • vertex in fiducial volume rVTX  (40,150) cm • kaon track can be extrapolated to the I.P. (time info) Neutral and Charged Kaon Meeting – 7 May 2007

  4. fit window p* cut The method • mn peak: p*(p mass) distribution from “m-cluster” sample • pp0 peak: p*(p mass) distribution requiring the p0 • 3-body decays: p*(p mass) distribution from MC • N.B.for 1) and 2)bin by bin MC corrections are applied. tagb estimated from MC kpm04 Neutral and Charged Kaon Meeting – 7 May 2007

  5. MC bin by bin correction: pp0 old shape The final shape used in the fit (shapeFIT) is obtained applying a bin by bin MC correction to shape from the DATA control sample (shapeDATA), accounting for distortions due to the control sample selection DATA Large MC corrections needed p* (MeV) Neutral and Charged Kaon Meeting – 7 May 2007

  6. MC bin by bin correction: pp0 new shape • Xp0 decay vtx selection • d_fromClu < 28 cm • vertex from signal selection green = mc true red = selected p*(MeV) Smaller MC Correction needed Neutral and Charged Kaon Meeting – 7 May 2007

  7. Conclusions: last meeting • The quality of the fit on the peaks is poor • The disagreement on the pp0 and mn peaks signals • the difference between DATA and MC resolutions • The population of each bin of the p*p+ distribution used for • the extraction of the MC bin by bin correction is crucial • Several methods to improve the situation have been tried • but unfortunately without the desired result • Possible solutions: • smearing the MC true distribution of p*p+ with the resolution • measured on DATA (using the mn from EMC selection) • 2) increase the bin width for the MC bin by bin corrections • 3) …. Neutral and Charged Kaon Meeting – 7 May 2007

  8. Output of the fit: last meeting Looking at the 7 sub-samples of 25 pb-1 each of 2002 data With the new shape The number of pp0 increases The difference is larger in two sub-samples detailed investigation needed The number of mn remains stable sub-sample Neutral and Charged Kaon Meeting – 7 May 2007

  9. Output of the fit: today Looking at the 7 sub-samples of 25 pb-1 each of 2002 data Now the raw counters from the two shapes are in agreement sub-sample Neutral and Charged Kaon Meeting – 7 May 2007

  10. Output of the fit: last meeting 25 pb-1 residuals Old shape New shape residuals normalized residuals normalized residuals p*(MeV) p*(MeV) Neutral and Charged Kaon Meeting – 7 May 2007

  11. Output of the fit: today 25 pb-1 residuals New shape Old shape residuals normalized residuals normalized residuals p*(MeV) p*(MeV) We have improved the quality of fit and the residuals Neutral and Charged Kaon Meeting – 7 May 2007

  12. What have been done • Smearing parameters to be applied to the MC momenta • have been obtained from the simultaneous fit of the p* • distributions from data control samples of pp0 and mn • decays • 2) Check the number of events used for the bin by bin • correction evaluation. Then going back to the fit of p*distribution to extract Npp|FIT a) for mn and pp0 shapes, the smearing parameters have been used to evaluate the MC bin by bin corrections b)for the shape of 3-body decays, the MC smeared distribution is used Neutral and Charged Kaon Meeting – 7 May 2007

  13. MC smearing pp0 sample mn sample DATA MC DATA MC p*(MeV) Applying a smearing to the MC momenta in the lab: the pp0 peak in the p* distribution from DATA is very well reproduced while the mn peak still exhibits a disagreement Neutral and Charged Kaon Meeting – 7 May 2007

  14. Results on 2002 DATA sample p*(MeV) Neutral and Charged Kaon Meeting – 7 May 2007

  15. Results on 2002 DATA sample Neutral and Charged Kaon Meeting – 7 May 2007

  16. pp0 mn p*(MeV) p*(MeV) Peaks on 2002 DATA sample Neutral and Charged Kaon Meeting – 7 May 2007

  17. Systematic effect (I) • Using the 2002 data sample and varying: • the starting point of the fit window (p*CUT) • the d_fromClu cut for the efficiency evaluation eDC cut 28 (26*) -> 32 cm dBR/BR 0.24 %(0.39%) p*CUT 165 -> 190 MeV/c dBR/BR 0.06 % (*) distorts the distribution used for efficiency evaluation Neutral and Charged Kaon Meeting – 7 May 2007

  18. Systematic effect (II) Using the 2002 data sample and comparing the results obtained with the New and the Old pp0 shapes New vs Old shape using the same d_fromClu maximum difference dBR/BR 0.16 % • new • old New vs Old shape d_fromClu = 30 cm and p*= 180 MeV dBR/BR 0.07 % Neutral and Charged Kaon Meeting – 7 May 2007

  19. Time stability Looking at the 7 sub-samples of 25 pb-1 each of 2002 data we have checked the time stability of the measurement p0 = 0.21042 ± 0.0005 sub-sample Neutral and Charged Kaon Meeting – 7 May 2007

  20. T3FILTER correction Using the whole DATA sample: BR(Kpp0())  BR x CT3 CT3 = 0.9994  0.0003 BRT3FILTER negligible O(10-6) Neutral and Charged Kaon Meeting – 7 May 2007

  21. FILFO correction Using the same set of runs for DATA and MC from BR(K()) studies: CFILFO = 1.00006  0.00032 (DATA) CFILFO = 0.99967  0.00015 (MC) In agreement within the errors BR(Kpp0())  BR x CFILFO BRFILFO = 3x10-4 The evaluation of CFILFO using exactly the signal selection is ongoing Neutral and Charged Kaon Meeting – 7 May 2007

  22. Conclusions and check list • The quality of the fit has been improved applying smearing parameters to the MC momenta measured in the lab. • A preliminary measurement of BR(Kpp0()) has been presented • Final corrections from cosmic ray veto and FILFO to be applied • The evaluation of systematic uncertainties is ongoing: • systematic effects from the selection cuts used for the efficiency control sample (now we have evaluated only for d_fromClu cut) • acceptance correction (use mc true value) and efficiency with K±X±p0decayvertex sample in FV and before DC inner wall • systematic effects from the fit : • mnshape • pp0new vs old shape  • 3 body decays shape • starting point of the fit window (p* cut)  • cosmic ray veto effect • FILFO effect negligible (see K+m+n(g)) • time stability on 2002 data  Neutral and Charged Kaon Meeting – 7 May 2007

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