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Blessing of the final result Blessing of the final result on BR(Kon BR(K++ ++0 0 (())))

E. De LuciaE. De Lucia

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Normalization sample is given by K-tag Number of K±±0 decays 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±0 control sample identified from 0 decay vertex

The absolute BR(KThe absolute BR(K) measurement) measurement

Measurement of Measurement of BR(KBR(K++++0 0

(())A new measurement is crucial in order to perform the fit to KA new measurement is crucial in order to perform the fit to K±± BR’s: BR’s:

only Kl3 and Kl3/K2 measured recently Kl3 and K2 are strongly correlated the available measurement dates back to Chiang ‘72 BR(K±±0) = (21,18 ± 0.28)% BR/BR = 1,3x10-2

but no radiative corrections & no correlations available

This decay enters in the normalization of BR(KThis decay enters in the normalization of BR(Kl3) by NA48, ISTRA+, E865 used for Vus l3) by NA48, ISTRA+, E865 used for Vus

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1)1) ttag on one side with Kag on one side with Kpreselection

-zPCA 20cm - PCA 10cm - pK (70,130) MeV

selection - VTX (40,150) cm - dp (-320,-120) MeV - p(m) (180,270) MeV

self-triggering tag (2 trigger sectors fired)

2) look for signal on the other sidelook 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 selectionSignal selection

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MCMETHOD

MCTRUE

DATAcut εε

ε)*ε(p

fit windowp* cut Tag bias estimated from MC kpm04

The methodThe method peak p*( mass) distribution from DATA control sample selected using

calorimetric information only + bin by bin MC corrections peak p*( mass) distribution from DATA control sample selected using

calorimetric information only + bin by bin MC corrections3-body decays p*( mass) distribution from MC smeared

p*(MeV)

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Efficiency evaluationEfficiency evaluation

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0

E,t,x

±

E,x,t

K tagt

pK

pKt0

xK

E,t,x

lK

d_fromClu

1) the K- track of the tagging side is extrapolated to the signal hemisphere to build the virtual K+ helix

Efficiency: control sample Efficiency: control sample selection selection K± X±0 decays in the signal FV are identified by their 0 decay

3) step along the virtual helix of the K+ to find the point giving the best evaluation of the the 0 decay vertex ( -like variable using s invariant mass and t, tDECAY(0)- tDECAY(K))

2) photon candidates of 0 decay among the neutral clusters with: 24° < CLU < 156o and t < tCLU < t + 70 ns

4) Estrapolate from the decay vertex, xK, to EMC with two-body hyp and evaluate the distance to the closest cluster and apply d_fromClu < 30 cm

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Efficiency: DATA vs MCEfficiency: DATA vs MC

MC for true 0

MC from methodDATA from method

DC (p*>p*CUT =180 MeV)

d_fromClu cut (cm)d_fromClu cut (cm)

DCDC

N.B.N.B. The geometrical acceptance,needed for efficiency evaluation from The geometrical acceptance,needed for efficiency evaluation from MC MC

If we ask for: efficiency control sample

selection decay vertex from signal selection

3% contamination from Kl3 decays3% contamination from Kl3 decaysselected 0 decaystrue 0 decays

p*+ (MeV)

0.00130.9896εεMCMETHOD

MCTRUE

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ResultsResults

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0.00050.3176cut)*(pεDC

Result on 2002 DATA Result on 2002 DATA samplesample

syststatTB 0.00010.00051.0106C 1,912818,347NFITππ

0.00031.0005CCRV

0.00030.98191/CFFFilfo

p*(MeV)

12,113,686 NTAG

p*(MeV)

ndf = 154/156 P(ndf)= 0.52

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Zoom on peaksZoom on peaks

p*(MeV)

p*(MeV)

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Fit residualsFit residualsResiduals Fit - Data

Normalized residuals

p*(MeV)

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Result using Tag KResult using Tag K22

* Updated

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Systematic effect (I): KSystematic effect (I): K±± lifetime in MClifetime in MCThe 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 obtainedvarying 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%BR/BR = 0.12%

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Systematic effect (II): FV Systematic effect (II): FV lower bound lower bound The requirement on the position of the signal decay vertex in the transverse plane (VTX) is: VTX(min) < VTX < VTX(max) VTX(min) = 40 cm VTX(max) = 150 cm

The resolution on the “neutral” vertex used for DC wrt the kine value is neu 1.5 cm at VTX(min) = 40 cm.

We have moved VTX (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%BR/BR = 0.17%

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Cross-check(I): tagging with Cross-check(I): tagging with KK2 2 The two tags, Tag K2 and Tag K2 , exhibit very different corrections

due to the FILFO filter

Therefore the measurement of BR(K++0()) with the Tag K2 provides us an excellent cross-check of BR(K++0()) done with the Tag K2 (*)

(*) the same efficiency has been used

0.00050.3182cut)*(pεDC 1,678621,612NFITππ

FFFilfo 1/C

9,352,915 NTAG

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Result using Tag KResult using Tag K22

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Cross-check (II): measure Cross-check (II): measure BR(KBR(K2(2())))

For the efficiency evaluation and correction, we have followed the same strategy used for our published paper and used the “-cluster” sample.

From the fit of the p* distribution we can extract the number of K2 decays with p*>225 MeV, integrating the K shape

statTB 0.00021.0164C 2,4432,443,780NCUT*P

12,113,686 NTAG 0.00070.9984ε

εMCMETHOD

MCTRUE

stat0.0963.63))(BR(K

CCC

1

cut)*(pε1

N

N)BR(K

CRVFFTBDCTAG

CUTP*)(

CFF = 1.0001 0.0003 CCRV = 1.0005 0.0003

syststat 0.150.0963.66))(BR(K KLOE ’06: PLB 632

we have measured -0.034 correlation between BR(Kwe have measured -0.034 correlation between BR(K2) and BR(K2) and BR(K2)2)

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Conclusions (I)Conclusions (I)

PDG06

Kτ

syststat0 0.00080.00050.2065))γ(ππBR(K

The measurement of the absolute BR(K+0()), inclusive of final

state

radiation, has been presented using both K2 and K2 tags:

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+0()) has been measured.

The weighted average of these two results, accounting for correlations is:

The BR dependence on the lifetime value has been measured

@MC

Kτ

@PDG06

Kτ

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Conclusions (II)Conclusions (II)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

KLOE BR(K±±0) = (20,65 ± 0.05stat ±0.08syst)% BR/BR = 4,6x10-3

FLAVIANET BR(K±±0) = (20,644 ± 0.080)% BR/BR = 3,9x10-3

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Conclusions (III)Conclusions (III)

BR(K2): PDG06 = (20,92 ± 0.12)% KLOE = (20,65 ± 0.05stat ±0.08syst)%

BR(Ke3)

BR(K3)

The impact of the KLOE BR(K2) on the BR(Kl3) measurements using as normalization the K2 channel (NA48/2 and ISTRA+). Comparison with what obtained with PDG BR(K2) and KLOE BR(Kl3)