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Measuring the branching ratio of the K 0 0 decay. KLOE Memo n° 279 – December 2002 E. Gorini, M. Primavera, A. Ventura. A. Ventura – 61 st KLOE General Meeting – Tor Vergata – 19-20/12/2002. ’ : World data vs. KLOE data. ’ K ± ± 0 0. Analyzed DATA sample
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Measuring the branching ratioof the K 00 decay KLOE Memo n° 279 –December 2002 E. Gorini, M. Primavera, A. Ventura A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
’ : World data vs. KLOE data ’ K±±00 • AnalyzedDATA sample • 112 pb–1(Aug-Sep 2002) • Monte Carlo samples • 1.5107all events • 7.5 105’ decays PDG(units 10–2) 1.73±0.04 (fit) 1.77±0.07 (average) Datarec DBV-14 reconstruction A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
’ event topology • Two tagging strategies: • K0“K’’ • K “K’’ 0 Self-triggering required for the tags + K+ – K– • EMC trigger • kpmfilt “tag” algo • Cluster splitting recovery • Track to cluster optimized 0 0 A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
Measurement of BR(’) Ntag = number of tagged events bckg = background fractions ’sel = efficiency to select ’ given the tag BR(0) = (98.7980.032)% CV = trigger cosmic veto efficiency FILFO = FILFO algorithm efficiency (1 – /’) = “tag bias” A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
Event selection • K/ Kself-tag • A K track according to any kpmfilt algo • A 2-track vertex with K@ r>25cm • Daughter track momentum: p*<135 MeV • 4 clusters on-time with vertex: Ei > 15 MeV , |(t–r/c)|<4 • Etot < 450 MeV K } vtx } clu Etot A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
Efficiency evaluation (I) All the efficiencies have been extracted on data by means of various Samples of Normalization. Systematic errors take into account the differences between the two tags used. MC has been used only for estimating background fractions. Tracking and vertexing • Only EMC variables used • Kseparately estimated for K+ and K–( nuclear interaction) v K = 0.466 0.001stat 0.003syst • vtxdependence onpstudied vtx = 0.539 0.001stat 0.003syst p A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
Efficiency evaluation (II) Clustering Aclu Aclu4 = 0.799 0.001stat 0.003syst • 4onTdepends on the tag { 4onT= 0.695 0.004 4onT= 0.744 0.004 E (MeV) • Studied systematics on the |(t–r/c)|<4cut • Checked wrong on-time cluster probability on data • Etot = 0.9942 0.0014 A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
Background evaluation Estimations on MC corrected by comparing with data • Tags: bckg = 0.37% bckg = 0.21% • Signal contaminations from: - Main K decays 0.46% - Kl400 decays 0.17% - Nuclear interactions 0.10% - Other rare K decays 0.03% - Other decays ~10–5 - Bhabha, “monotracks” ~10–5 bckg’ = (0.750.11)% A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
Systematics and corrections 4onT • Dependence of BR on the neutral cluster definition • Splitting recovery tuning • Minimum energy cut Emin>15 MeV • Differences in K and K tags for track/vertex efficiencies Ntag’/Ntag 0.74 0.72 0.7 13 15 17 Emin (MeV) Cosmic Veto : CV /CV’ = 0.99860.0008 FILFO algorithm: |FILFO /FILFO’ – 1| < 10–3 A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002
Results and perspectives BR(’) = (1.8070.008stat0.018syst)% Contributions to the total error (10–3 units) K,cluand many systematics coincide for Kee A. Ventura – 61st KLOE General Meeting – Tor Vergata – 19-20/12/2002