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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 – 27 February 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 neutral 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 Neutral and Charged Kaon Meeting – 27 February 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 – 27 February 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 tagb estimated from MC kpm04 Neutral and Charged Kaon Meeting – 27 February 2007

  5. true pp0 decays d (cm) routinetta from Paolo M. d_fromClu cut true 3 bodies decays P* p0(MeV) New vs Old efficiency (method) New (d_fromClu cut) Old ( p*(p0)asymmetric cut ) extrapolate from the neutral vtx to EMC with two-body hyp. then evaluate the distance to the closest cluster {d_fromClu } K  X p0 K p p0 Kl3 sp* 18 MeV 30 cm zoom @ peak P*p0(MeV) 0.5s 1s 1s 1.5s Neutral and Charged Kaon Meeting – 27 February 2007

  6. New vs Old efficiency (correction) New (d_fromClu cut) Old ( p*(p0)asymmetric cut ) eDC MC for true pp0 MC from method DATA from method -s 0 -1.5s -0.5s eDC (p*>p*CUT =180 MeV) p*(p0)asymmetric cut d_fromClu cut (cm) mc method/mc true ~ 1.01 mc method/mc true ~ 0.88 Neutral and Charged Kaon Meeting – 27 February 2007

  7. selected pp0 decays true pp0 decays New vs Old efficiency (contamination) Contamination from Kl3decays in the distribution of the momentum of the charged decay particle in the kaon rest frame assuming the pion mass Old ~11% P*p+ (MeV) New ~3% P*p+ (MeV) Neutral and Charged Kaon Meeting – 27 February 2007

  8. pp0 old shape • The final shape is obtained from a bin by bin MC correction • Comparison with the DATA shape with cosq*pp selection DATA MC Large MC corrections needed p* (MeV) p* (MeV) Neutral and Charged Kaon Meeting – 27 February 2007

  9. The new pp0shape • Neutral vtx selection • d_fromClu < 28 cm • charged vtx from signal selection green = mc true red = selected p*(MeV) Smaller MC Correction needed Neutral and Charged Kaon Meeting – 27 February 2007

  10. Fit results (with 1/3 of first 100 pb-1 ) Consider the first 100 pb-1 and use 1 pb-1 every 3 pb-1  ~35 pb-1 (to account for different data taking conditions) With the new method for the efficiency and the new shape for the pp0 peak starting point of the fit window p*p+ = 180 MeV/c residuals p*(MeV) p*(MeV) normalized residuals Neutral and Charged Kaon Meeting – 27 February 2007

  11. New shape Systematic effect (I) Using previously defined ~35 pb-1 and varying the starting point of the fit window (p*CUT) and the d_fromClu cut for the efficiency evaluation eDC d_fromClu cut 26 -> 32 cm dBR/BR 0.56% p*CUT 165 -> 190 MeV/c dBR/BR 0.2 % Neutral and Charged Kaon Meeting – 27 February 2007

  12. new old Systematic effect (II) Using ~35 pb-1 previously defined and comparing the results obtained with the new and the old pp0 shapes new vs old shape dBR/BR 0.33 % Neutral and Charged Kaon Meeting – 27 February 2007

  13. Fit result (with 2/3 of first 100 pb-1 ) Consider the first 100 pb-1 and use 2 pb-1 every 3 pb-1 With the new method for the efficiency and the new shape for the pp0 peak starting point of the fit window p*p+ = 180 MeV/c residuals p*(MeV) p*(MeV) normalized residuals Neutral and Charged Kaon Meeting – 27 February 2007

  14. First result (with 2/3 of first 100 pb-1 ) • Reduction of the systematic uncertainty from • the efficiency evaluation varying d_fromClu cut • dBR/BR 0.56%  0.4 % • But • Increase of the systematic uncertainty from • the starting point of the fit window (p*CUT) • dBR/BR 0.20% 0.38 % • the pp0 shape • dBR/BR 0.33% 0.76 % Neutral and Charged Kaon Meeting – 27 February 2007

  15. First result (2/3 vs 1/3 of first 100 pb-1 ) Consider the first 100 pb-1 and use 2 pb-1 every 3 pb-1 With the new method for the efficiency and the new shape for the pp0 peak starting point of the fit window p*p+ = 180 MeV/c residuals 2/3 sample 1/3 sample residuals p*(MeV) normalized residuals normalized residuals Neutral and Charged Kaon Meeting – 27 February 2007

  16. New vs Old shape (with 2/3 of first 100 pb-1 ) Using the new method for the efficiency and the old shape for the pp0 peak starting point of the fit window p*p+ = 180 MeV/c NEW OLD residuals p*(MeV) p*(MeV) normalized residuals Neutral and Charged Kaon Meeting – 27 February 2007

  17. New vs Old pp0Shape: output of the fit 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 – 27 February 2007

  18. Conclusions • 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 – 27 February 2007