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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 Blessing Meeting – 19 December 2007
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(Kl3) 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 p0gg decay vertex Blessing Meeting – 19 December 2007
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
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
Efficiency evaluation Blessing Meeting – 19 December 2007
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 p0gg decay • the K- track of the tagging side is extrapolated to the signal hemisphere to build the virtual K+ helix • photon candidates of p0gg 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 p0gg 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
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
Results Blessing Meeting – 19 December 2007
Result on 2002 DATA sample c2/ndf = 154/156 P(c2 ,ndf)= 0.52 p*(MeV) p*(MeV) Blessing Meeting – 19 December 2007
pp0 mn p*(MeV) p*(MeV) Zoom on peaks Blessing Meeting – 19 December 2007
Fit residuals Residuals Fit - Data p*(MeV) Normalized residuals Blessing Meeting – 19 December 2007
Result using Tag Km2 * Updated Blessing Meeting – 19 December 2007
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
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
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
Result using Tag Kp2 Blessing Meeting – 19 December 2007
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
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
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
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