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Single Top search

Single Top search. K. Nakamura Univ. of Tsukuba. Contents. Motivation Current Study and CDF NOTE Signal/Background Sample Lepton ID Jet Energy Correction MET Correction Event selection B-tagging Summery and Plan. - Signal acceptance study using S+J B-tagging. Motivation. |V tb |.

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Single Top search

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  1. Single Top search K. Nakamura Univ. of Tsukuba Contents • Motivation • Current Study and CDF NOTE • Signal/Background Sample • Lepton ID • Jet Energy Correction • MET Correction • Event selection • B-tagging • Summery and Plan - Signal acceptance study using S+J B-tagging

  2. Motivation |Vtb| |Vtb| • Produced electroweakly coupling • Direct access to W-t-b vertex • ssingletop~|Vtb|2 • Top-polarization study and V-A structure of EW top interaction • Background study for SM Higgs search • Exactly the same final state as WH->Wbb • Background of all channels to use W+njet background • Probe b-quark PDF (t-channel) • Non-SM phenomena • Heavy W’ boson • Anomalous W-t-b coupling …… t-channel s-channel But… Cross section is small (~40% of stt) Larger background cause of W+2jets bin Not established a significant evidence yet …

  3. Current Study and CDF NOTE Event selection and MC validation • Signal Acceptance and Monte Carlo based backgrounds (CDF 7863) • Validation of single-top signal samples (CDF 7701) Anlysis with 0.7 fb-1 (CDF 8112) • Non-W and W+njets (n=1,2,3) background estimation • Neural network b-tagger (CDF 7816) • Kinematics fitter for top quark reconstruction (CDF 749) • Construct discriminates with Neural network with Likelihood ratio Result Projections for Single Top Sensitivity Phys. Rev. D 71, 012005 (2005)

  4. Signal Sample Generator : Mad Event Event : single top s-channel LO Top Mass : Mt=175 GeV Catalin Ciobanu 11/10/2005, Top Properties Workshop

  5. Lepton ID Standard tight lepton selection of lepton+jet group. Detail is in appendix Electron Et>20 GeV Isolated Conversion Veto Muon Pt>20 GeV/c Isolated Cosmic Veto

  6. Jet Energy Correction Level4 Jet Energy Correction – not to apply abs correction Et>15 GeV, Eta < 2.8 MET Et Et is corrected with lepton and Level4 jets Phi Et>20 GeV Et/Pt(n) Phi/Phi(n) L4 Jet … 0.8 L5 Jet … ~1

  7. Event Selection Cross check This is t-channell result but… (96%) (90%) (25%) (24%) (24%) (24%) (23%) (21%)

  8. B-tagging Performance of SecVtx and JetProb b-tagging Number of events of under histogram include W+njet (n>0) final state For the statistics of the signal double SecVtx tag is applied, about 70% statistics are increased to use S+J tagging.

  9. Jet multiplicity distribution of b-tag performance SecVtx JetProb 19.2% 64.7% 13.6% 2.1% 0.3% Cross check • Use Jprob<0.05 cuts for Jet Prob. Jet multiplicity distribution after b tag (CDF 7863) Good agreement !?

  10. Double tag SecVtx + SecVtx SecVtx + JetProb About 68 % statistics of the 2 tag events is increased to use S+J tagging We can use 30% of tight jets to combine s+s & s+j tagging >>> about half of at least 1 secvtx tag

  11. W+nP Background n=2,3 W+2P 13 W+3P 30 Statistics of the background is small… But we confirmed ~10 times rejection power

  12. Summery and Plan • Double tag included s+j tagging has potential to improve s/n ratio and significance. • statistics of the signal is increased 1.68 x s-s tag • We can use 30% of tight jets to combined s-s s-j tag • About 10 times rejection power is estimated with W+nP sample. • Detail of signal selection will have to be confirmed. • We will apply this double-tag method to other “non-b” background like 3jets . • We will estimate signal significance and discovery potential as the function of luminosity…… Because of just started , we have many “TO DO”……

  13. Backup

  14. CEM ele ID PHX ele ID

  15. m ID

  16. Gen info after geometrical cuts lepton electron muon L5 MET correction

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