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Single Top search

Single Top search. - Significance study using S+J B-tagging. K. Nakamura Univ. of Tsukuba. Motivation. |V tb |. |V tb |. Produced electroweakly coupling Direct access to W-t-b vertex s singletop ~|V tb | 2 Top-polarization study and V-A structure of EW top interaction

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Single Top search

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  1. Single Top search - Significance study using S+J B-tagging K. Nakamura Univ. of Tsukuba

  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) (CDF 8286) Anlysis with 0.7 fb-1 (CDF 8112) NEW • 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. Backgrounds • Data based background Non-W Mistags Wbb Wcc Wc • MC based background

  5. Event Selection • Lepton ID Standard tight lepton selection of lepton+jet group. Detail is in appendix Muon Electron Pt>20 GeV/c Isolated Cosmic Veto Et>20 GeV Isolated Conversion Veto • Jet Energy Correction Level4 Jet Energy Correction – not to apply abs correction Et>15 GeV, Eta < 2.8 • MET Et is corrected with lepton and Level4 jets Et>20 GeV

  6. Signal/Background Expectation @1fb-1

  7. NN discriminants The 2 jets bin networks have 14 input variables.  The 14 input variables for 2 jet bin networks are shown in backup slide

  8. NN b-tagger This NN b-tagger is applied to jets that are already tagged by SecVtx tagger.

  9. Likelihood Function Analysis t-channel Likelihood function uses 7 variables s-channel Likelihood function uses 6 variables

  10. Motivation of our analysis t-channel |Vtb| |Vtb| s-channel Large amount of Background for this channel. About half of the background comes from Mistags and Wc(c). Double tag is the powerful method to reject these background for s-channel ! CDF NOTE 8112 But, statistics of the signal is limited by low efficiency of double tag. We plan to apply “tight” + “loose” b-tagging S+J SecVtx JetProb

  11. Signal Sample Generator : Mad Event Event : single top s-channel LO Top Mass : Mt=175 GeV Name : ttop0oNew Background Sample Generator : Alpgen + pythia Event : W(->e)+nP W(->mu)+nP (n = 0,1,2,3,4) Name : ltop0n - ltop4n ltop0m – ltop4m

  12. Estimated b-tag performance of each method for s-channel SecVtx Use Jprob<0.05 30% events in 2-jet bin can be tagged as s+s or s+j. >>> which corresponds to 46% of at least 1 secvtx tagged events in 2-jet bin.

  13. W+nP Background with MC sample e2 e2 e2 e2 e1 e1 e1 e1 e3 e3 e3 e3 e4 e4 e4 e4 Mistag Matrix At least 1 S 2 S Over estimate SS+SJ Under estimate SS+SJ Null-corr 100%-corr

  14. W(->e)+nP Background n=0,1,2,3,4 over under

  15. over under W+nP Normalized to 0.7 fb-1 ~1/40

  16. s-channel significance 99.7 (46%) 11.4 (14%) 2.2 (2.5%) 0.56(2.5%) 4.8 (2.5%) 113.3 26.7 7.3 (46%) s-channel 26.0 (46%) 0.74 (25%)

  17. Summary • Double tag including s+j tagging has a potential to improve the s/n ratio and significance. • 30% events in 2-jet bin can be tagged as s+s or s+j tag • The fraction of s+s or s+j tagged events is 46% of at least 1 tag events • According to very rough estimation, • Detail of signal selection will be confirmed. • We will examine some kinematics variables for background rejection. • We will estimate the sensitivity for single-top production as a function of integrated luminosity…… improve CDFNOTE Double tag Plan

  18. Backup

  19. CEM ele ID PHX ele ID

  20. m ID

  21. MC based background

  22. Non-W background

  23. Mistag background

  24. W+HF background

  25. NN input

  26. t-channel Likelihood valuables

  27. 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

  28. 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

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

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

  31. 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.

  32. 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 !?

  33. W(->m)+nP Background n=0,1,2,3,4 over under

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