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Updates on BR(K + π + π 0 ) E. De Lucia
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Transcript of Updates on BR(K + π + π 0 ) E. De Lucia
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
Updates on BR(KUpdates on BR(K++ππ++ππ00))
E. De LuciaE. De Lucia
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 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(KN.B. This decay enters in the normalization of BR(Kl3) by NA48, ISTRA+, E865l3) 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:Method:
The starting pointThe starting point
• Global efficiency TRK+VTX from neutral vertex technique:
asymmetric p*(0) cut (old method) ~~12% correction from mc_method/mc_true 12% correction from mc_method/mc_true + 11% Kl3 contamination11% Kl3 contamination
d_fromClu cut (new method) ~~1% correction from mc_method/mc_true 1% correction from mc_method/mc_true + 3% Kl3 contamination3% Kl3 contamination
• The shape for the The shape for the peak: old vs new method peak: old vs new method
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
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
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
MCMETHOD
MCTRUE
DATA ε
εε
1) peak: p*( mass) distribution from “-cluster” sample
2) peak: p*( mass) distribution requiring the
3) 3-body decays: p*( mass) distribution from MC
fit windowp* cut
tagb x cut)*(pε
1N
N)ππBR(K
DCTAG
FITππ0
tagb estimated from MC kpm04
The methodThe method
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
New vs Old efficiency New vs Old efficiency (method)(method)
New (d_fromClu cut)New (d_fromClu cut) Old ( p*(Old ( p*(00)asymmetric cut ))asymmetric cut )
P*0(MeV)
K X 0
K
Kl3
zoom @ peakzoom @ peak
10.5
11.5
p* 18 MeV
P* 0(MeV)
d
(cm
)
true 0 decays
true 3 bodies decays
d_fromClu cutd_fromClu cut
routinetta fro
m Paolo M.
routinetta fro
m Paolo M.
extrapolate from the neutral vtx to EMC with two-body hyp. then evaluate the distance to the closest cluster {d_fromClu }
30 cm
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
New vs Old efficiency New vs Old efficiency (correction)(correction)
mc method/mc true ~ 1.01
MC for true 0
MC from methodDATA from method
DCDC
DC DC (p*>p*CUT =180 MeV)
New (d_fromClu cut)New (d_fromClu cut) Old ( p*(Old ( p*(00)asymmetric cut ))asymmetric cut )
mc method/mc true ~ 0.88
p*(p*(0)asymmetric cut0)asymmetric cutd_fromClu cut (cm)d_fromClu cut (cm)
- -1.5-0.5
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
)( 0MCshape
))peak(p( * 0MCshape
New vs Old efficiency New vs Old efficiency (contamination)(contamination)
OldOld
selected 0 decaystrue 0 decays
P*+ (MeV)
New New
Contamination from Kl3decays in the distribution of the momentum of the charged decay particle in the kaon rest frame assuming the pion mass
P*+ (MeV)
~11%~11%
~3%~3%
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
old shapeold shape•The final shape is obtained from a bin by bin MC correction• Comparison with the DATA shape with cos
selection DATA
π0)(vtxshapeπ0)(shape
π0)x(vtxshape MC
MCDATA
p* (MeV)
π0)(vtxshapeDATA
)cosπ0(vtxshapeDATA *
p* (MeV)
MC
)cosπ0(vtxshapeMC *
)true( 0 shapeMC
Larg
e MC
Larg
e MC
corre
ctions n
eeded
corre
ctions n
eeded
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
The new The new shapeshape
Neutral vtx selection d_fromClu < 28 cm charged vtx from signal selection
green = mc truered = selected
p*(MeV)
Smaller M
C
Smaller M
C
Correcti
on needed
Correcti
on needed
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
Fit results Fit results (with 1/3 of first 100 pb(with 1/3 of first 100 pb--
1 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 0 peakstarting point of the fit window p*+ = 180 MeV/c
normalized residuals
residuals
p*(MeV) p*(MeV)
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
Systematic effect (I)Systematic effect (I)Using previously defined ~35 pb-1 and varying the starting point of the fit window (p*CUT ) andthe d_fromClu cut for theefficiency evaluation New shapeNew shape
p*p*CUT CUT
165 -> 190 MeV/cBR/BR 0.2 %
DC DC
d_fromClu cut 26 -> 32 cmBR/BR 0.56%
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
Systematic effect (II)Systematic effect (II)Using ~35 pb-1 previously definedand comparing the results obtained with the new and theold 0 shapes
new vs old shapeBR/BR 0.33 %
new
old
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
Fit result Fit result (with 2/3 of first 100 pb(with 2/3 of first 100 pb--
1 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 0 peakstarting point of the fit window p*+ = 180 MeV/c
normalized residuals
residuals
p*(MeV) p*(MeV)
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
First result First result (with 2/3 of first 100 pb(with 2/3 of first 100 pb-1 -1 ))
Reduction of the systematic uncertainty from
• the efficiency evaluation varying d_fromClu cut
BR/BR 0.56% 0.4 %ButBut
Increase of the systematic uncertainty from
•the starting point of the fit window (p*CUT )
BR/BR 0.20% 0.38 %
•the 0 shape
BR/BR 0.33% 0.76 %
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
First result First result (2/3 vs 1/3 of first 100 pb(2/3 vs 1/3 of first 100 pb-1 -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 0 peakstarting point of the fit window p*+ = 180 MeV/c
normalized residuals
residuals
p*(MeV)normalized residuals
residuals1/3 sample1/3 sample
2/3 sample2/3 sample
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
New vs Old shape New vs Old shape (with 2/3 of first 100 (with 2/3 of first 100 pbpb-1 -1 ))
Using the new method for the efficiency and the old shape for the 0 peakstarting point of the fit window p*+ = 180 MeV/c
NEW OLD
residuals
normalized residuals p*(MeV) p*(MeV)
E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007
New vs Old New vs Old Shape: output of the Shape: output of the fitfit
With the new shape
The number of 0 increases
The difference is larger intwo sub-samplesdetailed 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 Lucia Neutral and Charged Kaon Meeting – 27 February 2007
ConclusionsConclusionsThe quality of the fit on the peaks is poor
The disagreement on the 0 and peaks signalsthe difference between DATA and MC resolutions
The population of each bin of the p*+ distribution used forthe 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)2) increase the bin width for the MC bin by bin corrections3) ….