E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Updates on BR(K +  π + π 0 ) E. De Lucia

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 PDG fit ‘06 BR(K ±  ±  0 ) = (20,92 ± 0.12)%  BR/BR = 5,7x10 -3 CHIANG ’72 BR(K ±  ±  0 ) = (21,18 ± 0.28)%  BR/BR = 1,3x10 -2 N.B. This decay enters in the normalization of BR(K  l3) by NA48, ISTRA+, E865 Self-triggering K -    tag Fitting the distribution of the momentum of the charged decay particle in the kaon rest frame assuming the pion mass (p*) Method: The starting point Global efficiency  TRK+VTX from K ±  X ±  0 decay vertex technique:  asymmetric p*(  0 ) cut (old method) ~12% correction from mc_method/mc_true 11% Kl3 contamination ~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 ~1% correction from mc_method/mc_true + 3% Kl3 contamination The shape for the   peak: old vs new method The shape for the   peak: old vs new method investigating on the results obtained investigating on the results obtained

E. De LuciaNeutral and Charged Kaon Meeting – 7 May )tag on one side with K  preselection -  z PCA   20cm -  PCA  10cm - p K  (70,130) MeV selection -  VTX  (40,150) cm - dp  (-320,-120) MeV - p  (m  )  (180,270) MeV self-triggering tag (2 trigger sectors fired) look for signal on the other side 2) look for signal on the other side vertex in fiducial volume  VTX  (40,150) cm kaon track can be extrapolated to the I.P. (time info) Signal selection

E. De LuciaNeutral and Charged Kaon Meeting – 7 May )  peak: p*(  mass) distribution from “  -cluster” sample 2)   peak: p*(  mass) distribution requiring the   3) 3-body decays: p*(  mass) distribution from MC N.B. for 1) and 2) bin by bin MC corrections are applied. fit window p* cut tagb estimated from MC kpm04 The method

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

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007  X  0 decay vtx selection  d_fromClu < 28 cm  vertex from signal selection green = mc true red = selected p*(MeV) Smaller MC Correction needed MC bin by bin correction:   new shape

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Conclusions: last meeting The quality of the fit on the peaks is poor The disagreement on the  0 and  peaks signals the difference between DATA and MC resolutions The population of each bin of the 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: 1)smearing the MC true distribution of p*  + with the resolution measured on DATA (using the  from EMC selection) measured on DATA (using the  from EMC selection) 2) increase the bin width for the MC bin by bin corrections 3) ….

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Output of the fit: last meeting With the new shape The number of  0 increases The difference is larger in two sub-samples detailed investigation needed The number of  remains stable sub-sample Looking at the 7 sub-samples of 25 pb -1 each of 2002 data

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Output of the fit: today sub-sample 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

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

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

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 What have been done 1)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  0 and  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 N   FIT a) for  and  0 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

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 MC smearing Applying a smearing to the MC momenta in the lab: the  0 peak in the p* distribution from DATA is very well reproduced while the  peak still exhibits a disagreement   sample  sample DATA MC DATA MC p*(MeV)

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Results on 2002 DATA sample p*(MeV)

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Results on 2002 DATA sample Fractional Uncertainty on BR(K  0 (  )) Signal counting + Shape Stat0.23% Global efficiency0.15% Efficiency MC correction0.13% Tag bias0.05% Total0.30%

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Peaks on 2002 DATA sample   p*(MeV) 

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 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 p* CUT 165 -> 190 MeV/c  BR/BR 0.06 %  DC cut 28 (26 * ) -> 32 cm  BR/BR 0.24 %  BR/BR 0.24 % (0.39%) (*) distorts the distribution used for efficiency evaluation

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Systematic effect (II) Using the 2002 data sample and comparing the results obtained with the New and the Old  0 shapes New vs Old shape using the same d_fromClu maximum difference  BR/BR 0.16 % new New vs Old shape d_fromClu = 30 cm and p*= 180 MeV  BR/BR 0.07 %  old

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 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 sub-sample p0 = ±

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 Using the whole DATA sample: BR(K  0 (  ))  BR x C T3 C T3 =   BR T3FILTER negligible O(10 -6 ) T3FILTER correction

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 C FILFO =  (DATA) C FILFO =  (MC) Using the same set of runs for DATA and MC from BR(K  (  )) studies: In agreement within the errors  BR FILFO = 3x10 -4 BR(K  0 (  ))  BR x C FILFO FILFO correction The evaluation of C FILFO using exactly the signal selection is ongoing

E. De LuciaNeutral and Charged Kaon Meeting – 7 May 2007 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  0 (  )) 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 ±  0 decay vertex sample in FV and before DC inner wall  systematic effects from the fit :   shape   0 new vs old shape  3 body decays shape  starting point of the fit window (p* cut)  cosmic ray veto effect  FILFO effect negligible (see K +  + (  ))  time stability on 2002 data