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Blessing of the final result on BR(K +  p + p 0 ( g ) ) E. De Lucia

Blessing of the final result on BR(K +  p + p 0 ( g ) ) E. De Lucia. Measurement of BR(K +  p + p 0 ( g) ). A new measurement is crucial in order to perform the fit to K ± BR’s: only Kl3 and Kl3/K p 2 measured recently Kl3 and K p 2 are strongly correlated

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Blessing of the final result on BR(K +  p + p 0 ( g ) ) E. De Lucia

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  1. Blessing of the final result on BR(K+ p+p 0 (g))E. De Lucia Blessing Meeting – 19 December 2007

  2. Measurement of BR(K+p+p 0 (g)) • A new measurement is crucial in order to perform the fit to K± BR’s: • only Kl3 and Kl3/Kp2 measured recently • Kl3 and Kp2 are strongly correlated • the available measurement dates back to Chiang ‘72 BR(K±p±p0) = (21,18 ± 0.28)%DBR/BR = 1,3x10-2 • but no radiative corrections & no correlations available This decay enters in the normalization of BR(Kl3) by NA48, ISTRA+, E865 used for Vus The absolute BR(Kp2) measurement • Normalization sample is given byK-m-n tag • Number of K±p±p0decays from the fit of the distribution of the momentum of the charged decay particle in the kaon rest frame assuming the pion mass (p*) • Selection efficiency related to Drift Chamber information only and measured directly on DATA using the K±X±p0 control sample identified from p0gg decay vertex Blessing Meeting – 19 December 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) Blessing Meeting – 19 December 2007

  4. fit window p* cut The method mn peak p*(p mass) distribution from DATA control sample selected using calorimetric information only + bin by bin MC corrections pp0 peak p*(p mass) distribution from DATA control sample selected using calorimetric information only + bin by bin MC corrections 3-body decays p*(p mass) distribution from MC smeared Tag bias estimated from MC kpm04 p*(MeV) Blessing Meeting – 19 December 2007

  5. Efficiency evaluation Blessing Meeting – 19 December 2007

  6. d_fromClu Ep,xp,tp xK p± pK lK Kmn tag tm t0 pK p0 Eg,tg,xg Eg,tg,xg Efficiency: control sample selection K± X±p0 decays in the signal FV are identified by their p0gg decay • the K- track of the tagging side is extrapolated to the signal hemisphere to build the virtual K+ helix • photon candidates of p0gg decay • among the neutral clusters with: • 24° < qCLU < 156o and tf < tCLU < tf + 70 ns 3)step along the virtual helix of the K+ to find the point giving the best evaluation of the the p0gg decay vertex ( c2-like variable using gs invariant mass and Dt, tDECAY(p0)- tDECAY(K)) 4) Estrapolate from the decay vertex, xK, to EMC with two-body hyp andevaluate the distance to the closest clusterand apply d_fromClu < 30 cm Blessing Meeting – 19 December 2007

  7. true pp0 decays selected pp0 decays p*p+ (MeV) MC for true pp0 MC from method DATA from method eDC (p*>p*CUT =180 MeV) d_fromClu cut (cm) Efficiency: DATA vs MC • If we ask for: • efficiency control sample selection • decay vertex from signal selection • 3% contamination from Kl3 decays eDC N.B. The geometrical acceptance,needed for efficiency evaluationfrom MC Blessing Meeting – 19 December 2007

  8. Results Blessing Meeting – 19 December 2007

  9. Result on 2002 DATA sample c2/ndf = 154/156 P(c2 ,ndf)= 0.52 p*(MeV) p*(MeV) Blessing Meeting – 19 December 2007

  10. pp0 mn p*(MeV) p*(MeV) Zoom on peaks Blessing Meeting – 19 December 2007

  11. Fit residuals Residuals Fit - Data p*(MeV) Normalized residuals Blessing Meeting – 19 December 2007

  12. Result using Tag Km2 * Updated Blessing Meeting – 19 December 2007

  13. Systematic effect (I): K± lifetime in MC The geometrical acceptance is taken from MC simulation and its value is strongly related to the charged kaon lifetime. The relation between BR and lifetime values has been obtained varying the lifetime in a range of ±1% around the value used in our MC According to the present uncertainty of the KLOE lifetime measurement K± /K± = 0.24% we get:BR/BR = 0.12% Blessing Meeting – 19 December 2007

  14. Systematic effect (II): FV lower bound The requirement on the position of the signal decay vertex in the transverse plane (rVTX) is: rVTX(min) < rVTX < rVTX(max)rVTX(min) = 40 cm rVTX(max) = 150 cm The resolution on the “neutral” vertex used for eDC wrt the kine valueis rneu  1.5 cm at rVTX(min) = 40 cm. We have moved rVTX (min) from 38 to 42 cm using 1 cm steps, evaluating signal count, efficiency and correction to the efficiency. The contribution to the systematic uncertainty is BR/BR = 0.17% Blessing Meeting – 19 December 2007

  15. Cross-check(I): tagging with Kp2 The two tags, Tag Km2 and Tag Kp2 , exhibit very different corrections due to the FILFO filter Therefore the measurement of BR(K+p+p0(g)) with the Tag Kp2 provides us an excellent cross-check of BR(K+p+p0(g)) done with the Tag Km2 (*) (*)the same efficiency has been used Blessing Meeting – 19 December 2007

  16. Result using Tag Kp2 Blessing Meeting – 19 December 2007

  17. KLOE ’06: PLB 632 Cross-check (II): measure BR(Km2(g)) • From the fit of the p* distribution we can extract the number of Km2 • decays with p*>225 MeV, integrating the Km2shape For the efficiency evaluation and correction, we have followed the same strategy used for our published paper and used the “m-cluster” sample. CFF = 1.0001  0.0003 CCRV = 1.0005  0.0003 • we have measured -0.034 correlation between BR(Kp2) and BR(Km2) Blessing Meeting – 19 December 2007

  18. Conclusions (I) • The measurement of the absolute BR(K+p+p0()), inclusive of final state radiation, has been presented using both Km2 and Kp2 tags: • The weighted average of these two results, accounting for correlations is: @ • The BR dependence on the lifetime value t has been measured @ • The measurement of BR(K++()) using the fit of the p* distribution has been performed and it is in agreement with our published value. The correlation factor with BR(K+p+p0()) has been measured. Blessing Meeting – 19 December 2007

  19. Conclusions (II) 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 KLOE BR(K±p±p0) = (20,65 ± 0.05stat ±0.08syst)%DBR/BR = 4,6x10-3 FLAVIANET BR(K±p±p0) = (20,644 ± 0.080)%DBR/BR = 3,9x10-3 Blessing Meeting – 19 December 2007

  20. Conclusions (III) • The impact of the KLOE BR(Kp2) on the BR(Kl3) measurements using as • normalization the Kp2 channel (NA48/2 and ISTRA+). • Comparison with what obtained with PDG BR(Kp2) and KLOE BR(Kl3) BR(Ke3) BR(Km3) BR(Kp2): PDG06 = (20,92 ± 0.12)% KLOE = (20,65 ± 0.05stat ±0.08syst)% Blessing Meeting – 19 December 2007

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