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

E. De Lucia Neutral and Charged Kaon Meeting – 7 May 2007

Updates on BR(KUpdates on BR(K++ππ++ππ00))

E. De LuciaE. De Lucia


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 K±X±0 decay 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 investigating on the results obtainedinvestigating on the results obtained


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


MCMETHOD

MCTRUE

DATA ε

εε

1) peak: p*( mass) distribution from “-cluster” sample2) peak: p*( mass) distribution requiring the

3) 3-body decays: p*( mass) distribution from MC

N.B. for 1) and 2) bin by bin MC corrections are applied.

fit windowp* cuttagb estimated from MC kpm04

The methodThe method

tagb

1

cut)*(pε1

N

N)ππBR(K

DCTAG

FITππ0


MC bin by bin correction: MC bin by bin correction: old old shapeshapeThe final shape used in the fit (shapeshapeFITFIT) is obtained applying a bin by bin MC correction to shape from the DATA control sample (shapeshapeDATADATA), accounting for distortions due to the control sample selection

DATA

π0)(vtxshapeπ0)(shape

π0)x(vtxshapeshape MC

MCDATA FIT

p* (MeV)

π0)(vtxshapeDATA

Larg

e MC

Larg

e MC

corre

ctions n

eeded

corre

ctions n

eeded


X0 decay vtx selection d_fromClu < 28 cm vertex from signal selection

green = mc truered = selected

p*(MeV)

Smaller M

C

Smaller M

C

Correcti

on needed

Correcti

on needed

MC bin by bin correction: MC bin by bin correction: new new shapeshape


Conclusions: Conclusions: last meetinglast meetingThe 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)1) smearing the MC true distribution of p*smearing the MC true distribution of p*+ with the resolution+ with the resolution measured on DATA (using the measured on DATA (using the from EMC selection)from EMC selection)2) increase the bin width for the MC bin by bin corrections3) ….


Output of the fit: Output of the fit: last meetinglast meeting

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


Output of the fit: Output of the fit: todaytoday

sub-sample

Looking at the 7 sub-samples of 25 pb-1 each of 2002 data

Now the raw counters Now the raw counters from the two shapes from the two shapes are in agreementare in agreement


Output of the fit: Output of the fit: last last meetingmeeting

p*(MeV)

residuals

normalized residuals

Old shapeOld shape

p*(MeV)

residuals


New shapeNew shape

25 pb-1


Output of the fit: Output of the fit: todaytoday

p*(MeV)

residuals


Old shapeOld shape

p*(MeV)

residuals


New shapeNew shape

25 pb-1

We have improved the quality of fit and the residualsWe have improved the quality of fit and the residuals


What have been doneWhat have been done1)Smearing parameters to be applied to the MC momenta have been obtained from the simultaneous fit of the p*distributions from data control samples of 0 and decays 2) Check the number of events used for the bin by bin correction evaluation.

Then going back to the fit of p*distribution to extract NFIT

a) for and 0 shapes, the smearing parameters have been used to evaluate the MC bin by bin corrections

b) for the shape of 3-body decays, the MC smeared distribution is used


MC smearingMC smearing

Applying a smearing to the MC momenta in the lab:the 0 peak in the p* distribution from DATA is very well reproduced while the peak still exhibits a disagreement

sample sample

DATA MC

DATA MC

p*(MeV)


MCMETHOD

MCTRUE

DATADC εε

εcut)*(pε

tagb

1

cut)*(pε1

N

N)ππBR(K

DCTAG

FITππ0

Results on 2002 DATA Results on 2002 DATA samplesample

syststat 0.00010.00051.0106tagb

p*(MeV)

0.06521.048)ππBR(K 0

1912818347NFITππ

12113686 NTAG

MeV 180 cut*p


MCMETHOD

MCTRUE

DATADC εε

εcut)*(pε

tagb

1

cut)*(pε1

N

N)ππBR(K

DCTAG

FITππ0

Results on 2002 DATA Results on 2002 DATA samplesample

syststat 0.00010.00051.0106tagb

0.06521.048)ππBR(K 0

1912818347NFITππ

12113686 NTAG

MeV 180 cut*p

Fractional Uncertainty

on BR(K0())

Signal counting + Shape Stat 0.23%

Global efficiency 0.15%

Efficiency MC correction 0.13%

Tag bias 0.05%

Total 0.30%

0.00131.0105εεMCMETHOD

MCTRUE


Peaks on 2002 DATA Peaks on 2002 DATA samplesample

p*(MeV)

p*(MeV)


Systematic effect (I)Systematic effect (I)Using the 2002 data sample and varying: the starting point of the fit window (p*CUT ) the d_fromClu cut for the efficiency evaluation

p*p*CUT CUT

165 -> 190 MeV/cBR/BR 0.06 %BR/BR 0.06 %

DC DC

cut 28 (26*) -> 32 cmBR/BR 0.24 %BR/BR 0.24 % (0.39%)

(*) distorts the distribution used for efficiency evaluation


Systematic effect (II)Systematic effect (II)Using the 2002 data sample and comparing the results obtained with the New and the Old 0 shapes

New vs Old shapeNew vs Old shapeusing the same d_fromClumaximum differencemaximum differenceBR/BR 0.16 %BR/BR 0.16 %

new

New vs Old shapeNew vs Old shaped_fromClu = 30 cmand p*= 180 MeVBR/BR 0.07 %BR/BR 0.07 %

old


Time stabilityTime stabilityLooking at the 7 sub-samples of 25 pb-1 each of 2002 datawe have checked the time stability of the measurement

sub-sample

p0 = 0.21042 ± 0.0005


Using the whole DATA sample:

13

13

64

64

FLAGT

TAGTAG

FLAGTSIGSIG

TAG

SIG

xNN

xNN

N

N

BR(K0()) BR x CT3

CT3 = 0.9994 0.0003

BRT3FILTER negligible O(10-6)

T3FILTER correction T3FILTER correction


SIGTAG

TAGFILFOC

1

1iFILFO

iAFILFO

iAFILFO

i NN

N

CFILFO = 1.00006 0.00032 (DATA)CFILFO = 0.99967 0.00015 (MC)

Using the same set of runs for DATA and MC from BR(K()) studies:

In agreement within the errorsIn agreement within the errors

BRFILFO = 3x10-4BR(K0()) BR x CFILFO

FILFO correctionFILFO correction

The evaluation of CFILFO using exactly the signal selection is ongoing


Conclusions and check listConclusions and check list The quality of the fit has been improved applying smearing parameters to the MC momenta measured in the lab. A preliminary measurement of BR(K0()) has been presented Final corrections from cosmic ray veto and FILFO to be applied The evaluation of systematic uncertainties is ongoing:

systematic effects from the selection cuts used for the efficiency control sample (now we have evaluated only for d_fromClu cut) acceptance correction (use mc true value) and efficiency with

K±X±0 decay vertex sample in FV and before DC inner wall systematic effects from the fit :

shape 0 new vs old shape 3 body decays shape starting point of the fit window (p* cut)

cosmic ray veto effect FILFO effect negligible (see K++()) time stability on 2002 data

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

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