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Significance of Single Top Study Using B-Tagging Methodology at University of Tsukuba

This study at Tsukuba University focuses on the significance of single top quark production using B-tagging techniques. The research aims to understand the coupling of top quarks with W bosons and investigate non-Standard Model interactions. By analyzing t-channel and s-channel processes, the study explores the potential of anomalous W-t-b couplings and the presence of heavy W’ bosons. Experimental results and projections offer insights into background rejection strategies and the sensitivity of single top production with integrated luminosity. Novel techniques such as neural networks and kinematic fitting enhance the analysis of top quark events.

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Significance of Single Top Study Using B-Tagging Methodology at University of Tsukuba

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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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