Updates on BR(K + π + π 0 ) E. De Lucia

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E. De Lucia Neutral and Charged Kaon Meeting – 27 February 2007 Updates on BR(K Updates on BR(K + + π π + + π π 0 0 ) ) E. De Lucia E. De Lucia

description

Updates on BR(K +  π + π 0 ) E. De Lucia. The starting point. PDG fit ‘06 BR(K ±  p ± p 0 ) = (20,92 ± 0.12)% D BR/BR = 5,7x10 -3 CHIANG ’72 BR(K ±  p ± p 0 ) = (21,18 ± 0.28)% D BR/BR = 1,3x10 -2 N.B. This decay enters in the normalization of BR(K  l3) by NA48, ISTRA+, E865. - PowerPoint PPT Presentation

Transcript of Updates on BR(K + π + π 0 ) E. De Lucia

Page 1: 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

Page 2: Updates on BR(K +  π + π 0 ) E. 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

Page 3: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 4: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 5: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 6: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 7: Updates on BR(K +  π + π 0 ) E. De Lucia

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%

Page 8: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 9: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 10: Updates on BR(K +  π + π 0 ) E. De Lucia

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)

Page 11: Updates on BR(K +  π + π 0 ) E. De Lucia

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%

Page 12: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 13: Updates on BR(K +  π + π 0 ) E. De Lucia

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)

Page 14: Updates on BR(K +  π + π 0 ) E. De Lucia

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 %

Page 15: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 16: Updates on BR(K +  π + π 0 ) E. De Lucia

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)

Page 17: Updates on BR(K +  π + π 0 ) E. De Lucia

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

Page 18: Updates on BR(K +  π + π 0 ) E. De Lucia

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) ….