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Status of K l3 analysis. Charged Kaon Meeting 10 March 2005 - LNF. Barbara Sciascia. 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. - PowerPoint PPT Presentation
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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
3 Barbara Sciascia –10 Mar 05 - LNF
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
4 Barbara Sciascia –10 Mar 05 - LNF
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
5 Barbara Sciascia –10 Mar 05 - LNF
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
6 Barbara Sciascia –10 Mar 05 - LNF
Signal selection-2
Spectrum of m2lept for 2001-2002 data-set, Tag K+2
K00
K0
K nucl.int..
7 Barbara Sciascia –10 Mar 05 - LNF
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)
8 Barbara Sciascia –10 Mar 05 - LNF
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
9 Barbara Sciascia –10 Mar 05 - LNF
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.
10 Barbara Sciascia –10 Mar 05 - LNF
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.
11 Barbara Sciascia –10 Mar 05 - LNF
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
12 Barbara Sciascia –10 Mar 05 - LNF
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
13 Barbara Sciascia –10 Mar 05 - LNF
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
14 Barbara Sciascia –10 Mar 05 - LNF
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.
Dat
a/M
C r
atio
Electrons and Positrons 2002
cos()
cos()
15 Barbara Sciascia –10 Mar 05 - LNF
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.
16 Barbara Sciascia –10 Mar 05 - LNF
Single photon efficiency-2
• 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.
17 Barbara Sciascia –10 Mar 05 - LNF
Single photon efficiency-3
• 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.
18 Barbara Sciascia –10 Mar 05 - LNF
Single photon efficiency-4
• 2001-2002 Data, and kpm04 and all_phys MC have been used.
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Single photon efficiency-5
• The Data/MC ratio of efficiencies is used to correct MC photon energies.
• Barrel and Endcaps are corrected separately.
20 Barbara Sciascia –10 Mar 05 - LNF
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.
21 Barbara Sciascia –10 Mar 05 - LNF
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.
22 Barbara Sciascia –10 Mar 05 - LNF
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.)
23 Barbara Sciascia –10 Mar 05 - LNF
Systematics
Verbose
24 Barbara Sciascia –10 Mar 05 - LNF
Dat
a/M
C r
atio
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()
25 Barbara Sciascia –10 Mar 05 - LNF
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
26 Barbara Sciascia –10 Mar 05 - LNF
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.
27 Barbara Sciascia –10 Mar 05 - LNF
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
28 Barbara Sciascia –10 Mar 05 - LNF
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
29 Barbara Sciascia –10 Mar 05 - LNF
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 =
30 Barbara Sciascia –10 Mar 05 - LNF
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%.
31 Barbara Sciascia –10 Mar 05 - LNF
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
32 Barbara Sciascia –10 Mar 05 - LNF
Kaon nuclear interactions-2
VTX(cm)
Dat
a/M
C r
atio
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
33 Barbara Sciascia –10 Mar 05 - LNF
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)
34 Barbara Sciascia –10 Mar 05 - LNF
Fit of m2 distribution-2
The residuals in each period, show the same trend.
35 Barbara Sciascia –10 Mar 05 - LNF
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
36 Barbara Sciascia –10 Mar 05 - LNF
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.