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Barbara Sciascia

K  semileptonic decays: status report. Charged Kaon Meeting October, 26 st - LNF. Barbara Sciascia. Outline. Tag bias Cosmic veto/T3 correction Efficiency determination: e ( p 0 ). m -. K -. g. K +. e +. g. Tag selection. Tag events with a K   m  n : track from IP

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Barbara Sciascia

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  1. K semileptonic decays: status report Charged Kaon Meeting October, 26st - LNF Barbara Sciascia

  2. Outline • Tag bias • Cosmic veto/T3 correction • Efficiency determination: e(p0)

  3. m- K- g K+ e+ g Tag selection • Tag events with a Kmn: • track from IP • momentum cut: • 70 MeV pK  130 MeV • decay vertex in fiducial volume: • 40cm  rVTX  150 cm • 2-body decay identified in kaon rest frame: • p(mm): 3s cut • track pointing into the calorimeter • Associated cluster on the Barrel with E>90 MeV (e99%) • Emc Trigger satisfied by muon cluster (30%) Absolute BR measurement via a Tag technique.

  4. m- K- g K+ e+ g Signal selection • Kl3 selection: • 1-prong kaon decay vertex in the fiducial volume • 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: Absolute BR measurement via a Tag technique. tdecayK = tlept -Llept /(bleptc) = tg-Lg/c • 2 further kinematical cuts to reject background from Kt and Kp2 decays.

  5. Selection efficiency Tag bias correction Fit results N(Kl3)  (eTAG(i) BR(i)) 1 aC BR(Kl3) = NTAGeTAG(Kl3)eSELE Cosmic veto/T3 correction 3 samples [e(KAON+VTX+TRK) e(TCA)e(p0)]DATA eSELE= eSELE_MC [ e(KAON+VTX+TRK) e(TCA)e(p0) ]MC

  6. Measuring BR(Kl3) • 12 Tag samples: Km2 + m-trigger • Kp2 + p0-trigger • Km2 + Global_Emc-trigger • Counting Kl3 from fit. • KPM04 MC production. • Tag bias: trigger and kinematics stability checked • Cosmic veto correction • Selection efficiencies: • Tracking: global, from Paolo Massarotti; • syst. at 0.3% level. • Track-to-Cluster: from neutral kaons (Paolo Branchini). • p0: from single photon efficiency • (work is in progress, Simone dell’Agnello).

  7. Tag bias: stability wrt tag kine selection • Stability of tag-bias value wrt the cut around the “p* 2-body peak” • Select events with a n-s cut around the peak: • 236 MeV for Km2, m-trig • 205 MeV for Kp2, p0-trig • TB stable within the errors (now: 3s cut for both Ke3 and Km3).

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. (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 0.1% for all samples. • The contribution to the final error is negligible (10-4) Ke3 Km3 m2(MeV2)

  13. p0-from-vertex efficiency - Old Kp2 kinematic selection MC DATA • P0 reconstruction efficiency is estimated as a function of p0 momentum, from Kpp0 decays. • DATA/MC ratio is flat: • 97.70  0.09 % Pmiss (MeV) eDATA/eMC

  14. 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.

  15. 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.

  16. 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.

  17. Single photon efficiency-4 • 40 pb-1 of 2002 Data and 2002 MC all_phys have been used. • Data and MC have different resolutions in p* and in cluster selection variables.

  18. Conclusions • The tag bias is stable wrt the kinematical cut applied for the selection of the different tag samples. • A first study of the trigger efficiency for K events has been presented, using two different metod. The agreement between MC and Data is very good within the errors • The evaluation of the correction due to the cosmic veto has been presented. • Work is in progress for the p0 efficiency: single-photon efficiency correction applied on MC. • The NEW KPM04 MC reduces the MC statistics contribution to the BR measurements by a factor 3. • The study of the systematics related to efficiency determination has to be completed, taking correlations into account.

  19. Spare slides Spare slides

  20. On the way towards p0 efficiency Emin(MeV) Emin(MeV) pp0kine(MeV) Kpp0 (MC) Kl3 (MC) • Single-photon efficiency measured with Kp2 events. • The low component of the p0 momentum spectrum for Kl3 events span a region of Eminwhich is fully contained in the Emin range of Kp2 decays. • Plenty of statistics to minimize contribution to efficiency error.

  21. Single photon efficiency. Data/MC-Old

  22. Single photon efficiency. Data/MC-New • 20 pb-1 of Data and MC (KPM04)

  23. A note on Kpm MC statistics • The errors on Kl3 BR measurements are at 2% level. • They are dominated by the Kpm MC statistics • As an example: • BR(K+e3) = (4.8xx  0.110)% • with: 0.110 %  (0.033 0.102 0.025)% From the fit [e(KAON+VTX+TRK) e(TCA)e(p0)]DATA eSELE= eSELE_MC [ e(KAON+VTX+TRK) e(TCA)e(p0) ]MC • A Kpm-MC campaign with 1/1 MC statistics wrt to Data will lower the MC sample contribution to the error from 2% to  0.5%

  24. KPW04 - Conclusions • A selection has been presented aiming at measuring absolute Kl3 BR, on a sample of Km2 tagged decays. • The signal events has selected using a ToF technique (m2lept spectrum is obtained). • Further kinematic cuts are applied to reduce residual background contamination. • Result of the fit on the m2leptspectrum gives a yield of 200k Ke3 decays on the whole 2001-2002 data sample. • Selection efficiency is taken from MC, with DATA/MC correction for what concern K+Vtx+Trk, TCA and p0 efficiencies. • The contributions to the fractional error on BR(Ke3) are 0.6% from the fit and 1% from the efficiency • A first attempt has been performed in order to extract the slope of the form factor l+ from a fit of the Dalitz plot of Ke3 decay. • The study of the systematics related to efficiency determination has to be completed, taking correlations into account.

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