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Search for Singletop production

Search for Singletop production. Univ. of Tsukuba S Kim, K Nakamura. Introduction Double tag Kinematics TODO. Motivation of Double tag. t-channel. |V tb |. |V tb |. s-channel. Large amount of Background for this channel. About half of the background comes from

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Search for Singletop production

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  1. Search for Singletop production Univ. of TsukubaS Kim, K Nakamura • Introduction • Double tag • Kinematics • TODO

  2. Motivation of Double tag 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 ! At least 1tag 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

  3. Event Selection • Lepton ID Standard tight lepton selection of lepton+jet group. 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 But event selection of this talk is unexacting… We will move into gen6 soon!

  4. Double tag

  5. Double tag performance Pretag at least 1 tag category A) category B) A) + B) s-channel 100% 64.2% 17.5% 11.9% 29.4% Wbb 100% 52.4% 11.1% 8.6% 19.7% ttbar 100% 57.2% 12.0% 8.9% 20.9% Mistag 100% 1.92% 0.05% 0.11% 0.16% Wcc 100% 13.2% 0.5% 1.5% 2.0% We can use two type of b-tagging methods. SECVTX : Lxy based alg. JETPROB: d0(each track) based alg. We can use below two categories of double tag. A) SECVTX + SECVTX B) SECVTX + JETPROB (not include category A) Performance for the 2-jet-bin

  6. Process Event Yield @L=955 pb-1 At least 1tag category A) + B) Wbb 162.80±48.69 61.21 Wcc 60.71±16.95 9.5 Wc 76.54±17.94 #1.9 Total Heavy flaver 300.05±83.08 72.61 Non-W 19.98±4.77 #0.49 Mistags 133.36±10.67 3.3 Total data-based background 453.40±83.90 76.4 WW 4.96±0.39 #0.6 WZ 7.56±0.50 ZZ 0.24±0.02 Z->ee 1.28±0.10 Z->mm 5.59±0.44 Z->tt 4.88±0.38 ttbar l+j 37.37±2.47 8.57 ttbar DIL 19.27±1.32 12.10 Total MC-based background 81.14±2.95 21.3 Single Top s-channel 15.44±0.98 7.07 Single Top t-channel 22.36±1.81 ---

  7. s-channel specific kinimatics study

  8. S-channel single top event @ CM Frame n l t W* b b ambiguity Selection of bjet from top quark t-channel : tagged jet -> 95% s-channel : tagged jet -> 53% top mass resolution +15 GeV Selection of neutrino Pz solution 30% … no solution CDFNOTE Mlnb : for 4 cases This Top Mass constraint gave some bias to Mlnb distribution??

  9. Likelihood Function for neutrino Pz 2 solution case 0 or 1 solution case Move three parameters: METx METy PnZ

  10. PnZ @GenLev PnZ *Qlep @Sim n n l- l+ t t W*- W*+ b b P P d - u u - d +Z b b ---- W*+ ---- W*- ---- correct ---- wrong correct wrong PnZ PnZ PnZ*Qlep

  11. Good agreement! recPnZ recPnZ genPnZ genPnZ 2 solutions : no solution = 71.6% : 28.4% Probability to choose correct solution : 75.2% (of 2 solutions case)

  12. Likelihood Function for bbbar ambiguity Using L5 jet No b jet correction Sim Lev Sim Lev -- from top -- from W* -- from top -- from W* bjet Pt Mlb

  13. cosfb x Qlep @ Wstar Rest Frame n n l- l+ t t W*- W*+ f b b P P f +Z b b tb production process has the V-A coupling, so it is easy for the b-jet to be produced in the direction of quark in proton, and bbar-jet to be produced in the direction of anti-quark in anti-proton @ the Wstar rest frame. cosfangle shown in upper figure times lepton charge is the powerful variable to select b-jet which is directory produced from Wstar.

  14. cosfb distribution bjet from top bjet from W* Gen Lev ----W*+ ---- W*- bjet from W* bjet from top Sim Lev

  15. cosfb x Qlep distribution Sim Lev Gen Lev -- from top -- from W* -- from top -- from W* Use these distribution as the Probability Density Function

  16. bbbar ambiguity Correct choice : 81% ! Mlnb distribution

  17. Likelihood for Event Selection signal Wbb MbbGeV MbbGeV PtbbGeV PtbbGeV

  18. Mlnb distribution at the best significance L=955fb-1 Before event selection After event selection S/N=6.0/61.7 S/sqN=0.75 S/N=5.4/39.3 S/sqN=0.86

  19. Summery&ToDo • Double tag including s+j tagging has a potential to improve the s/n ratio and significance. • This shows an expected performance • We examine some kinematics variables for eliminating ambiguity and background rejection. • We find a lot of effective variables. To Do in a couple of weeks • Signal selection will be reconfirmed with gen6. To Do in 3 months • We will improve JetProb tagger. • Estimation of Data based background • second lepton veto study? • make results for 1.2 or 2 fb-1 data • ………

  20. Backup

  21. Top Quark Production @ =1.96 TeV ppbar • ttbar pair production • SingleTop production sttbar=7.3±0.5±0.6±0.4 pb-1 ssingle=2.86±0.28 pb-1 stat syst lumi g W±

  22. Motivation of SingleTop Search |Vtb| |Vtb| • Produced electroweakly coupling • Direct access to W-t-b vertex • ssingletop~G(tbW)~|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 • Non-SM phenomena • Heavy W’ boson • Anomalous W-t-b coupling …… t-channel s-channel

  23. W* mass n l t W* b MW*2> Mt2+Mb2~ Mt2 b ^ MW* =q2=s W* has the mass as small as possible to keep larger than Mt…??

  24. cosfb x Qlep @ Wstar Rest Frame n n l- l+ t t W*- W*+ f b b P P f +Z b b cosfb x Qlep Sim Lev cosfb ----W*+ ---- W*- -- top -- other top other Sim Lev

  25. MW* @Sim Using L5 jet No b jet correction

  26. Likelihood … correlation check MW* PnZ *Qlep

  27. MET Double Gaussian

  28. Using L5 jet n l t W* b b B-jet Pt distribution No b jet correction Gen Lev Sim Lev -- top -- other -- top -- other Use these distribution as the Probability Density Function

  29. Using L5 jet n l t W* b b Mlb distribution No b jet correction Gen Lev Sim Lev -- top -- other -- top -- other Use these distribution as the Probability Density Function

  30. Parameter correlation These figure shows some correlations between the Likelihood parameters…… But Likelihood is only used as the choosing bbbar ambiguity, so we use this likelihood !

  31. Top Specific Correlation Factor gen P – Rec P Rec P p0=2.12 p1=23.3 p2=0.057 p0=1.83 p1=24.8 p2=0.032 p0=1.31 p1=25.0 p2=0.081 From takeuchi-san From takeuchi-san From takeuchi-san Xaxis value of each bin is weighted mean distribution

  32. W boson direction at the W* rest frame Dominant channel of Wbb background is t-channel like upper right feynman diagram. -> W boson direction is close to p or pbar direction

  33. Signal W W f b f b t t d u d P P u W*- W*+ +Z @ Wstar Rest Frame b b Wbb b b b b u d u d f d u d u P P f + - + - +Z W W @ Wbb Rest Frame

  34. cosfw distribution generator level … w/ acceptance cut simulated

  35. cosfwxQlep distribution We can use this variable for event selection !

  36. Mtop(lnb) distribution At least 1 tag Double tag

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