Barbara Sciascia

1 Barbara Sciascia –10 Mar 05 - LNF Barbara Sciascia Barbara Sciascia

Status of KStatus of Kl3 analysisl3 analysis

Charged Kaon Meeting Charged Kaon Meeting 10 March 2005 - LNF10 March 2005 - LNF

2 Barbara Sciascia –10 Mar 05 - LNF

Outline

• Introduction• Tag: Selection and Tag bias.

• Signal: Selection and Fit procedure

• Efficiency: From MC. Data/MC corrections for Tracking, Track-to-Cluster, and Photon efficiencies.

• Systematics: Tag bias, Filfo, Cosmic veto/T3, Trigger, and K nuclear interaction corrections.

• Preliminary results: BR(K0e) and BR(K0

• Conclusions


Introduction

• Data sample: 2001+2002, w/o data quality.• MC: use both kpm04 and all_phys productions.• For handiness divided in 12+1 periods: 5 for the 2001 data, 7 for the 2002 data, 1 for the 2002 -peak-scan.

• Absolute BR(Kl3) measurement via a Tag technique.• Use 2 Tag: K2 + -trigger K2 + 0-trigger• 2 Tag 2 Charge 4 independent samples.• Counting Kl3 from the fit of a m2 distribution.• Effciency from MC + correction from Data/MC


Tag selection

KK

KK

ee

• track from IP, momentum cut: 70 MeV pK 130 MeV• decay vertex in fiducial volume: 40cm VTX 150 cm• daughter track extrapol. to EMC• 2-body decays identified in kaon rest frame: 3 cut around p peak p(m) = 236 MeV p(m) = 205 MeV• For K0 events look for a 0 from vertex using the (t) technique.• Emc Trigger satisfied by muon cluster (30%) 0 clusters (90%)

Tag events with a K or K0


Signal selection 1-prong kaon decay vertex in the

fiducial volume (40cm VTX 150 cm)

daughter track extrapol. to EMC Reject two-body decays: p(m) 195 MeV 0 search: 2 neutral clusters in

EmC, with ToF matching the K decay vertex (t)<3t)

Spectrum of charged daughter mass, m2, from TOF measurement:tdecay

K = tlept -Llept /(leptc) = t-L/c

KK

KK

ee

Fit with a linear combination of

Ke3 and K3 shapes, and background contribution.

Kl3 selection


Signal selection-2

Spectrum of m2lept for 2001-2002 data-set, Tag K+2

K00

K0

K nucl.int..


Background rejection-1

K00 + 0Dalitz decay, give a m2

lept under the Ke3 peak; they are rejected cutting on Emiss-Pmiss spectrum (<90MeV) (0 momentum from a kinematic fit)

K0 + early give a m2lept

under the K3 peak:• 0 momentum from a kinematic fit • Evaluation of missing momentum• Cut on momentum of the secondary track in the Pmiss rest frame (P>90 MeV)

Emiss-Pmiss (MeV)

K00

K0,

K0e

K0

K00

P(MeV)


Background rejection-2

• The previous cuts reject 96% of background events• The efficiency on the signal is: about 50% for both Ke3 and K3

K00

K0

K nucl.int.

The residual background is about 1.5% of the selected Kl3 sample


Fit of m2 distribution

Fit of the sample: • Tag K+2, Sig K-l3 • Data 2001+2002• MC kpm04 + all_phys

The residuals of the fit signal different Data-MC resolution and possibly a Data-MC shift.


Counting of the events

Tag K+2 Tag K+2 Tag K-2 Tag K-2

NTAG 22 451 780 8 770 461 23 038 024 8 389 453

Tag K+2 Tag K+2 Tag K-2 Tag K-2

NKe3 67 022 331 26 774 215 71 188 345 25 942 211

NK3 42 096 282 16 586 179 44 925 293 16 465 180

Number of events selected for each tag (2001+2002 runs):• The or the 0 clusters satisfy the EMC trigger requirement.• No cosmic veto or T3 selected events.

Number of events selected for each signal divided per tag:• Output of the fit• Fitting all the 2001-2002 sample, or fitting each period separately and adding together the events found, gives the same grand total within the errors.


The ingredients of the measure

BR(Kl3) = N(Kl3) (TAG(i) BR(i)) 1 NTAG(1-fNI) TAG(Kl3) SELE

Fit results Tag bias correction

[(KAON+VTX+TRK) TCA) 0)]DATA

(4 samples)

[(KAON+VTX+TRK) TCA) 0) ]MC

SELE= SELE_MC

C

Cosmic veto/T3correction

K nucl. int.correction


Kaon+vertex+track efficiency

Reconstruction efficiency for kaon 1-prong decay chain from events with a neural vertex reconstructed along the expected kaon decay path (from the TAG)

K+ K-

K+ K-

Period=12 (2002)

Period=3 (2001)

Use “global 1-prong” efficiency as a function of the transversal Vtx position (VTX).

Measure efficiencies on Data and MC and correct with Data/MC on a period-by-period basis


Track-to-cluster association efficiency-1

Negative muons

PositronsThe track-to-cluster (TCA) association efficiency is evaluated usingKL charged decays, specifically KLe3 and KL3, identified by kinematical selection.

The efficiency is evaluated in bin of track momentum and impinging angle. Ptrack(MeV)

MC

DATA


Track-to-cluster association efficiency-2

Electrons and Positrons 2001

The ratio of DATA/MC efficiency, computed as a function of the secondary track momentum and of the angle at the impinging point, is plugged into the computation selection efficiency.

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Electrons and Positrons 2002

cos()

cos()


Single photon efficiency-1

• Select events with K2 or K2 tag.• Unbias for the trigger: require Emc-trigger to - or 0-clusters, following the tag.• Ask for a K2 selection (p* cut) in the signal side. • Get 0 from the missing momentum at vertex.• Look for a 0-photon from the vertex, excluding clusters already used by the tag or connected to a track.



• Starting with K2+ selection, estimate the energy and the position of the “other photon”. • Look for a cluster close to the other photon.• “Close to” criteria: 1- distance between cluster and estimated position. 2- opening angle between estimated and cluster direction from the vertex.



• Measurement o the single photon efficiency as a function of estimated energy ot the photon, separately for different tags (K2 or K2) and charges.• The efficiency behaviour at high energy (similar to the KL0 measurement) indicate a not correct acceptance definition.



• 2001-2002 Data, and kpm04 and all_phys MC have been used.



• The Data/MC ratio of efficiencies is used to correct MC photon energies.

• Barrel and Endcaps are corrected separately.


Absolute BR(Ke3) measurement

Tag K-2Tag K+2 Tag K-2Tag K+2

Tag BR(Ke3) BR (UNCOR CORR) %

Tag K+2 5.185 0.053 (0.032 0.041)Tag K+2 5.203 0.075 (0.053 0.053)Tag K-2 5.237 0.048 (0.030 0.038)Tag K-2 5.231 0.075 (0.054 0.053)

• “Bare” efficiencies about 7% both for Ke3 and K3 in each tag sample.

• Uncorrelated errors between the 4 tag samples: Nsig, TB, CosmicVeto/T3, MC stat. used for efficiency evaluation.• Correlated error: TCA, Tracking, Photon efficiency corrections of MC efficiency.

• 2/nDof = 0.51 for the 4 measurements, uncorr. errors only.


Absolute BR(K3) measurements

Tag K-2Tag K+2 Tag K-2Tag K+2

Tag BR(K3) BR (UNCOR CORR) %

Tag K+2 3.599 0.051 (0.030 0.041)Tag K+2 3.538 0.067 (0.048 0.047)Tag K-2 3.726 0.051 (0.030 0.042)Tag K-2 3.760 0.071 (0.051 0.050)

• 2/nDof = 5.73 for the 4 measurements, uncorr. errors only.

• Nsig is evaluated in each sample separately, using the SAME FIT PROCEDURE systematic errors from the fit common to all samples.

• Agreement between different tags; separation between different charges.


Systematics: short mode • BR(K3): difference between charges check TCA correction for .

• Tag bias estimated from MC. • Contributions to the systematic error from: Trigger, Cosmic veto / T3, Filfo, and Kine selection.• A first and very conservative estimation of the contribution to syst. err. ranges from 0.18% to 0.44%, following tag and signal channels.

• Cosmic veto/T3 correction (C) evaluated directly on Data; negligible contribution to the systematic error (about 0.02%)

• Kaon nuclear interactions: some study to be finalized.

• Fit procedure: bad 2, bad residual distribution, period-dependent bkg…

• Systematic error from Data/MC efficiency corrections: work is in progress. The contribution from tracking is about 0.3% (P.M.)


Systematics

Verbose


Dat

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TCA efficiency: quality check

Muons 2001

cos()

The DATA/MC correction for TCA efficiency, is very different for positive e negative muons.

This difference is not present in the SpaGatti TCA efficiency corrections.

Try to measure TCA correction directly from decays in K2 events

Muons 2002

cos()


Trigger: EMC/DC-1

DC/EMC

EMC/DC

• Measure EmC-trigger efficiency wrt the DC trigger: (EMC/DC) (errors are statistical only)

Data MC

K 94.982 0.003 95.130 0.006

K 95.129 0.003 95.188 0.006

• (EMC/DC) is stable within the errors wrt the threshold requirement at the 2nd level DC trigger.

(EMC/DC) Data


Trigger: EMC/DC-2

CTRGData MC Truth

K 92.752 0.003 92.896 0.007

K 92.949 0.003 93.007 0.007

• From MC, evaluate the correlation factor, CTRG, between DC and EmC Trigger• Correct (EMC/DC) from data, using CTRG • Compare with MC truth (errors are statistical only):

• Difference at the 0.1 % level (0.14% for K and 0.06% for K)• First check of the reliability of Tag-bias measurement for what concern Emc-global-trigger.


Trigger: “Two-emisphere method”-1 • “Two-emisphere method” (KLOE memo 223) successfully used in studying trigger efficiency in neutral kaon analyses

KK

KK

ee

•Define: EMC=1 P(Tag=1)P(DarkSide=0) where:

- P(Tag=1): probability for the selected “Tag Emisphere” of firing only one trigger sector (here the -cluster)

- P(DarkSide=0): probability for “the rest of the event” (included machine bkg clusters) of not firing any sectors


Trigger: “Two-emisphere method”-2•The “division of the event” has a degree of arbitrarity which can be kept under control defining a MAX and a min probability for the selected list of clusters: P P; with P = PMAX PMin

• Good agreement within the errors between MC and Data• Reliability of the method: 0.8% of difference wrt the MC truth• Correcting data with factor C = EMC(MC)/EMC(MCtruth) we get EMC(Data) values in very good agreement with Mctruth.

• Good check of trigger effectson tag-bias evaluation.

EMC(Data) EMC(MC)

K 91.96 0.23 92.21 0.25

K 92.09 0.25 92.27 0.25

EMC (MCtruth)

92.896 0.007

93.007 0.007

CEMC(Data)

K 92.64 0.23

K 92.83 0.25


Cosmic ray veto – T3 correction

• The correction factor C can be evaluated directly on data, using T3 and Cosmic veto flags.

m2(MeV2)

Ke3 K3

•

• CT is evaluated in each Tag sample separately.• To evaluated CS a raw cut is applied in the m2 distribution to separate Ke3 and K3 events.• C is of the order of 1.0013 1.0025 for all samples.• The contribution to the final error is negligible (104)

(1+CS/S)

(1+CT/T)

C =


Tag bias

1- K Trig

2- K0 0-Trig

K () K ()

Ke3 -1.70 0.07 0.04 0.08

K -1.09 0.09 0.85 0.09

K () K ()

Ke3 0.49 0.13 2.51 0.14

K 1.20 0.17 3.09 0.17

• Good stability of tag-bias value wrt the cut around the “p* 2-body peak” : negligible contribution to the syst. error.• Small contribution to syst. error from FilFo and from the Trigger• Negligible contribution to syst. error from Cosmic veto/ T3 correction.• A very conservative estimation of the contribution to syst. err. ranges from 0.18% to 0.44%.


Kaon nuclear interactions

This fraction is about 1.7% for positive tags, 0.005% for negative tags (46 periods of about 10 pb-1, the last contains -scan runs).

Use fNI value to correct Ntag: Ntag Ntag(1- fNI)

Tag K-2

Tag K+2

Tag K-2

Tag K+2

fNI(%)

fNI(%)

For each Tag, evaluate the fraction fNI of “signal kaon” which has a nuclear interaction (from MC truth).

periods

periods


Kaon nuclear interactions-2

VTX(cm)

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Use a “special” (1 mm step fit) neutral vertex distribution to compare the kaon nuclear interaction in Data and MC.

From the Data/MC ratio, apparent excess on Data in correspondence of Beam pipe and Inner DC wall. Possibly different Data/MC resolution effect?

More investigation needed.

Beam pipe Inner DC wall


Quality of fit of the m2 distribution

The residuals for all the Tag samples show the same trend.

Tag K-2

Tag K+2

Tag K-2

The 2/nDoF distribution for the 12 periods (nDof ranges from 180 to 222)


Fit of m2 distribution-2

The residuals in each period, show the same trend.


Quality of fit of the m2 distribution-3The distribution of background fraction under Ke3 and K3 peaks (fit output) show a dependence from the period.

Tag K-2Tag K+2 Tag K-2

Correlation matrix: Ke3 - K3: about 4% Ke3 - Bkg: about 2%K3 - Bkg: about 30%

Without bkg rejection was:Ke3 - K3: about 4% Ke3 - Bkg: about 10%K3 - Bkg: about 80%

Tag K+2


Conclusions

• The measurement of the Ke3 and K3 absolute branching ratios has been presented.• 4 tag samples, on priciple independent, have been used.• The errors (fit procedure, efficiency evaluation and correction, MC stat. Used, Cv/T3 correction ) range from 1.0% and 1.4%, Ke3 and K3 in each sample.

• The 4 measurements show a good agreement for the Ke3• The Km3 measurements separate per charge: possible effect from the TCA correction for muons.

• First evaluation of the systematic error for the Tag bias and for the Cosmic veto/T3 corrections.

• The study of the systematics related to efficiency determination has to be completed.

Barbara Sciascia

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