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Barbara Sciascia

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.

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Barbara Sciascia

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  1. Status of Kl3 analysis Charged Kaon Meeting 10 March 2005 - LNF Barbara Sciascia

  2. 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(Kp0en) and BR(Kp0mn) • Conclusions

  3. 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 f-peak-scan. • Absolute BR(Kl3) measurement via a Tag technique. • Use 2 Tag: Km2 + m-trigger • Kp2 + p0-trigger • 2 Tag  2 Charge 4 independent samples. • Counting Kl3 from the fit of a m2 distribution. • Effciency from MC + correction from Data/MC

  4. m- K- g K+ e+ g Tag selection • track from IP, momentum cut: • 70 MeV pK  130 MeV • decay vertex in fiducial volume: • 40cm  rVTX  150 cm • daughter track extrapol. to EMC • 2-body decays identified in kaon • rest frame: 3s cut around p peak • p(mm) = 236 MeV • p(mp) = 205 MeV • For Kpp0 events look for a • p0 from vertex using the D(dt) • technique. • Emc Trigger satisfied by • muon cluster (e30%) • p0 clusters (e90%) Tag events with a Kmn or Kpp0

  5. m- K- g K+ e+ g Signal selection • 1-prong kaon decay vertex in the fiducial volume (40cm  rVTX  150 cm) • daughter track extrapol. to EMC • Reject two-body decays: p(mp)  195 MeV • p0 search: 2 neutral clusters in EmC, with ToF matching the K decay vertex (d(dt)<3st) • Spectrum of charged daughter mass, m2, from TOF measurement: Kl3 selection tdecayK = tlept -Llept /(bleptc) = tg-Lg/c • Fit with a linear combination of Ke3 and Km3 shapes, and background contribution.

  6. Signal selection-2 Spectrum of m2lept for 2001-2002 data-set, Tag K+m2 Kpp0 Kpp0p0 K nucl.int..

  7. Background rejection-1 Kpp0, pmn Kp0en Kpp0p0 Kp0mn Kpp0p0 P(MeV) Emiss-Pmiss (MeV) • Kpp0 + early pmn give a m2lept under the Km3 peak: • p0 momentum from a kinematic fit • Evaluation of missing momentum • Cut on momentum of the secondary track in the Pmiss rest frame (P>90 MeV) Kpp0p0 + p0Dalitz decay, give a m2lept under the Ke3 peak; they are rejected cutting on Emiss-Pmiss spectrum (<90MeV) (p0 momentum from a kinematic fit)

  8. Background rejection-2 • The previous cuts reject 96% of background events • The efficiency on the signal is: about 50% for both Ke3 and Km3 Kpp0p0 Kpp0 K nucl.int. The residual background is about 1.5% of the selected Kl3 sample

  9. Fit of m2 distribution • Fit of the sample: • Tag K+p2, 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. Counting of the events • Number of events selected for each tag (2001+2002 runs): • The m or the p0 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. The ingredients of the measure Tag bias correction Fit results N(Kl3)  (eTAG(i) BR(i)) 1 aC BR(Kl3) = NTAG(1-fNI)eTAG(Kl3)eSELE Cosmic veto/T3 correction (4 samples) K nucl. int.correction [e(KAON+VTX+TRK) e(TCA)e(p0)]DATA eSELE= eSELE_MC [ e(KAON+VTX+TRK) e(TCA)e(p0) ]MC

  12. 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- Use “global 1-prong” efficiency as a function of the transversal Vtx position (rVTX). Measure efficiencies on Data and MC and correct with Data/MC on a period-by-period basis Period=12 (2002) K+ K- Period=3 (2001)

  13. Track-to-cluster association efficiency-1 The track-to-cluster (TCA) association efficiency is evaluated usingKL charged decays, specifically KLe3 and KLm3, identified by kinematical selection. The efficiency is evaluated in bin of track momentum and impinging angle. Positrons MC DATA Ptrack(MeV) Negative muons

  14. Track-to-cluster association efficiency-2 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. Electrons and Positrons 2001 Data/MC ratio cos(q) Electrons and Positrons 2002 cos(q)

  15. Single photon efficiency-1 • Select events with Km2 or Kp2 tag. • Unbias for the trigger: require Emc-trigger to m- or p0-clusters, following the tag. • Ask for a Kp2 selection (p* cut) in the signal side. • Get bp0 from the missing momentum at vertex. • Look for a p0-photon from the vertex, excluding clusters already used by the tag or connected to a track.

  16. Single photon efficiency-2 • Starting with Kp2+g 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. Single photon efficiency-3 • Measurement o the single photon efficiency as a function of estimated energy ot the photon, separately for different tags (Kp2 or Kp2) and charges. • The efficiency behaviour at high energy (similar to the KLppp0 measurement) indicate a not correct acceptance definition.

  18. Single photon efficiency-4 • 2001-2002 Data, and kpm04 and all_phys MC have been used.

  19. Single photon efficiency-5 • The Data/MC ratio of efficiencies is used to correct MC photon energies. • Barrel and Endcaps are corrected separately.

  20. Tag K+m2 Tag K+p2 Tag K-m2 Tag K-p2 Absolute BR(Ke3) measurement • “Bare” efficiencies about 7% both for Ke3 and Km3 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. • c2/nDof = 0.51 for the 4 measurements, uncorr. errors only.

  21. Tag K+m2 Tag K+p2 Tag K-m2 Tag K-p2 Absolute BR(Km3) measurements • 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. • c2/nDof = 5.73 for the 4 measurements, uncorr. errors only.

  22. Systematics: short mode • BR(Km3): difference between charges  check TCA correction for m. • 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 (aC) evaluated directly on Data; negligible contribution to the systematic error (about 0.02%) • Kaon nuclear interactions: some study to be finalized. • Fit procedure: bad c2, 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. Systematics Verbose

  24. TCA efficiency: quality check 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 pm decays in Kp2 events Muons 2001 cos(q) Data/MC ratio Muons 2002 cos(q)

  25. Trigger: EMC/DC-1 • Measure EmC-trigger efficiency wrt the DC trigger: e(EMC/DC) (errors are statistical only) e(EMC/DC) Data • e(EMC/DC) is stable within the errors wrt the threshold requirement at the 2nd level DC trigger. DC/EMC EMC/DC

  26. Trigger: EMC/DC-2 • From MC, evaluate the correlation factor, CTRG, between DC and EmC Trigger • Correct e(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. m- K- g K+ e+ g Trigger: “Two-emisphere method”-1 • “Two-emisphere method” (KLOE memo 223) successfully used in studying trigger efficiency in neutral kaon analyses • Define: eEMC=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 m-cluster) - P(DarkSide=0): probability for “the rest of the event” (included machine bkg clusters) of not firing any sectors

  28. 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  dP; with dP = 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 = eEMC(MC)/eEMC(MCtruth) we get eEMC(Data) values in very good • agreement with Mctruth. • Good check of trigger effects • on tag-bias evaluation.

  29. (1+CS/S) aC = (1+CT/T) Cosmic ray veto – T3 correction • The correction factor aC can be evaluated directly on data, using T3 and Cosmic veto flags. • CT is evaluated in each Tag sample separately. • To evaluated CS a raw cut is applied in the m2 distribution to separate Ke3 and Km3 events. • aC is of the order of 1.0013 1.0025 for all samples. • The contribution to the final error is negligible (10-4) Ke3 Km3 m2(MeV2)

  30. Tag bias 1- Kmn m-Trig 2- Kpp0p0-Trig • 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. Kaon nuclear interactions For each Tag, evaluate the fraction fNI of “signal kaon” which has a nuclear interaction (from MC truth). fNI(%) Tag K+m2 Tag K+p2 This fraction is about 1.7% for positive tags, 0.005% for negative tags (46 periods of about 10 pb-1, the last contains f-scan runs). Use fNI value to correct Ntag: Ntag Ntag(1- fNI) periods fNI(%) Tag K-m2 Tag K-p2 periods

  32. Kaon nuclear interactions-2 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. rVTX(cm) Data/MC ratio Beam pipe Inner DC wall

  33. Quality of fit of the m2 distribution The residuals for all the Tag samples show the same trend. Tag K+m2 Tag K-m2 The c2/nDoF distribution for the 12 periods (nDof ranges from 180 to 222) Tag K-p2

  34. Fit of m2 distribution-2 The residuals in each period, show the same trend.

  35. Quality of fit of the m2 distribution-3 The distribution of background fraction under Ke3 and Km3 peaks (fit output) show a dependence from the period. Correlation matrix: Ke3 - Km3: about 4% Ke3 - Bkg: about 2% Km3 - Bkg: about 30% Without bkg rejection was: Ke3 - Km3: about 4% Ke3 - Bkg: about 10% Km3 - Bkg: about 80% Tag K+m2 Tag K+p2 Tag K-m2 Tag K-p2

  36. Conclusions • The measurement of the Ke3 and Km3 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 Km3 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.

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