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Few days before submitting the BR( ’) paper to Physics

Few days before submitting the BR( ’) paper to Physics Letters B (December 2003), an objection was raised to our evaluation of the ratio of tagging efficiencies in ’ (called “ tag bias ”). A dedicated meeting of K  group + F.Bossi was

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Few days before submitting the BR( ’) paper to Physics

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  1. Few days before submitting the BR(’) paper to Physics Letters B (December 2003), an objection was raised to our evaluation of the ratio of tagging efficiencies in ’ (called “tag bias”). • A dedicated meeting of K group + F.Bossi was held in Lecce (January 2004) in order to understand the discrepancies between different evaluations of “tag bias”. Misalignments in MC versions used in the analysis (2002) and later (2003) were found to be partially responsible for this. It was decided to wait for the last MC campaign (2004) to re-compute “tag bias” and re-check all the steps in the analysis which could be affected by such misalignments. • Since then, we have used all the MC releases produced in the meantime to:1)estimate the “tag bias”,2)check the consistency of our efficiency evaluation method and 3)understand the effect of the different MC scenario on the definition of the samples of normalization.

  2. N’tag Ntag 1 – ’ 1 – tag 1 BR(0)2 Rb’ KvtxAclu44onTEtot BR(’)= • Monte Carlo versions used : • “Old” MC  2002 production (analysis) • “New” MC 2003 production • “SuperNew” MC Feb 2004 (bugs on radiatives) • “HyperNew” MC Mar 2004 (bugs fixed) All ingredients in BR(’) have been recomputed one by one. No relevant differences wrt KLOE Note #187 found, except for: • Factor Rb’ introduced in BR formula (tag bias) • Ontime-clusters efficiency 4onTre-computed on data following the hints given by last MC’s

  3. Bias induced on signal selection • The so-called “Tag Bias” Rb includes effects from: • *) Event Trigger, *) Cosmic Veto, *) Event Classification, • *) Tag selection, *) Self-triggering conditions • It has been computed on Monte Carlo, as it was • discussed and decided last January in Lecce • Good agreement among various releases of last MC’s • Systematics on Rb evaluated from MC as fluctuations • among different MC releases Rb(K++00)2 = 1.1016  0.0082  0.0069 Rb(K++00)2 = 1.0587  0.0059  0.0047 Rb(K––00)2 = 1.0983  0.0081  0.0083 Rb(K––00)2 = 1.0544  0.0059  0.0080

  4. K+dcontamination (LAST MC’s): >12% (2 tag), >7% (2 tag) but… Efficiency of finding 4 ’s ontime Previously efficiencies were found to be : by imposing “Base”-cuts for K+d : 4 clusters such that: K+dcontamination (OLD MC): 3% (2 tag), 2% (2 tag)

  5. Data – MC comparison : Energies (I) Emin Emin+E’’ E’’’+Emax Emax

  6. Data – MC comparison : Energies (II) Etot E’’ M12 E’’’

  7. Data – MC comparison : Energies (III) E3 + E4 E1 + E2 E4= | E3+E4 – E1–E2| t’12

  8. Data – MC comparison : t2 Triangular cut : 360 – E4(MeV) < 40 t2 t2= min{[(t’1k2+t’2k2)/2]1/2}k=3,4

  9. Data – MC comparison : E4vs. t2 Triangular cut : 360 – E4(MeV) < 40 t2 Data E4 t2 MC Triangular cut : 360 – E4(MeV) < 40 t2 E4 t2

  10. Efficiency of finding 4 ’s ontime (now) Besides “Base”-cuts, further “strict” cuts are imposed for K+d The 4 clusters are such that: • Cuts have been tuned on LAST MC’s in order to • let the efficiency on new K+d reproduce the true 4onT • Systematic error evaluated by studying the sensitivity to cuts’ definitions Then, applying this additional set of cuts, efficiencies are found to be

  11. Conclusions BR(K++00)2 = ( 1.768  0.024  0.023 ) % BR(K++00)2 = ( 1.759  0.021  0.021 ) % BR(K––00)2 = ( 1.729  0.024  0.027 ) % BR(K––00)2 = ( 1.788  0.021  0.030 ) % BR(K++00) = ( 1.764  0.019  0.021 ) % BR(K––00) = ( 1.759  0.019  0.023 ) % BR(K00)2 = ( 1.748  0.017  0.021 ) % BR(K00)2 = ( 1.774  0.015  0.019 ) % BR(K00) = ( 1.765  0.013  0.022 ) % It was BR(K00) = ( 1.810  0.013  0.017 ) % on previous paper draft • KLOE Note #187 & Paper draft (= KLOE Note #190)updated

  12. Evaluation of 4onT through MC 4onT = Measured efficiency in K+d SoN P = Purity of K+d SoN after “strict” cuts (9596%) bckg = Efficiency of background of K+d  = Fraction of signal lost after “strict” cuts (7%) 4onT (rejected signal) true R = (65%) 4onT (total signal) true Strategy Cuts have been tuned on last MC’s so that 4onT and 4onT coincide true

  13. About K and vtx By using OLD-MC parameters: K = 0.46630.0032 By usingHYPERNEW-MCparameters: K = 0.46320.0032 where Pbckg goes from 1.6% (OLD) to 12% (HYPERNEW) On last MC’s vdoes not change even if background is increased v(MC)= 0.60060.0062 v(MC)= 0.60580.0058 computed on signal only computed on signal+ 12%bckg

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