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Study of top quark production in the semileptonic decay mode at the ILC

Study of top quark production in the semileptonic decay mode at the ILC. Philippe Doublet Roman Pöschl François Richard. Plan. Motivation Measurement method Efficiencies Results. The top quark and extra dimensions Geography and compositeness Top couplings. 1. motivation.

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Study of top quark production in the semileptonic decay mode at the ILC

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  1. Study of top quark production in the semileptonicdecay mode at the ILC Philippe Doublet Roman Pöschl François Richard

  2. Plan • Motivation • Measurementmethod • Efficiencies • Results

  3. The top quark and extra dimensions Geography and compositeness Top couplings 1. motivation

  4. The top quark and extra dimensions • Top quark : no hadronisation clean and detailed observations • Randal – Sundrummodelswithextra dimensions provide an elegantway to address the hierarchyproblem • A geographicalinterpretationof Yukawacouplingsisgiven • Thesemodelscanbeseen as dual to composite models(AdS/CFT correspondence) • In thesemodels, the top quark and the Higgs are compositeobjects

  5. Geography and compositeness • Higgs on IR brane for gauge hierarchyproblem • SM fermions have different locations along the 5th dimension • Overlaps leptons – Higgs in the 5th dimension generate good Yukawacouplingswith O(1) localisation parameters e0 t0 IR brane (TeV) UV brane (MPl) H Aµ0 bulk y (5th dim.) 0 πR

  6. Top couplings • Several RS modelspredictmodifiedleftgZ(tL) and right gZ(tR) top couplings to Z (via Z-ZKKmixing) Δg(tL)/g(tL) Δg(tR)/g(tR) SM 0,0 Djouadi [1]-1%,-34% Hosotani [2] +18%,-7% Carena [4] 0,-20% Gherghetta [3] -20%,-20%

  7. Observables Top quark cross section Measurementwith the ILD detector Reconstruction whithin the ILD framework Requirements Methodadopted 2. Measurementmethod

  8. Observables • Our goal : measuregZ(tL) and gZ(tR) precisely • Use of the simulation for the ILD detector at the ILC (1000fb-1) : top producedat500 GeV • How : measureσ(tt), ALR and AFB • From ALR and AFB, one deducesgZ(tL) and gZ(tR) couplings • Semileptonicdecaymode : tt(bW)(bW)(bqq)(blv) Gives top charge Allows reconstruction of the top quark

  9. Top quark cross section • σ(tt) ≈ 600 fbat 500 GeV(≈ 180 fb for SL top into e and µ) • Major background : ZWW (Zbb)≈ 8fb, sametopology • Almost background free

  10. Measurementwith the ILD detector • ILD optimised forParticle Flow technique(i.e. reconstructeveryparticle in a jet) • 3.5 T B-field • Performances : • Vertexing : σIP = 5 µm (+) 10 µm/p(GeV)sin3/2θ • Tracking : σ(1/pT) < 5.10-5GeV-1 • Granularcalorimetry : σE/E = 30%/√E

  11. Reconstruction whithin the ILD framework • tt(bW)(bW)(bqq)(blv) = semileptonicdecay mode • 1000 fb-1weregeneratedwithWhizard (6f final states e.g. bbcseve) • Full simulation isdonewith the ILD detector under GEANT4 (Mokka software) • « Objects » reconstructedwithParticle Flow algorithm (Pandora) • Data used : samplesprepared for the LOIs

  12. Requirements • ttbbqqlv (l=e,µ) • Needat least 1 b jet (vertex) • Find 1 lepton (tracking) • Method : • Find a lepton • Force 4 jets clustering • Findat least 1 (or 2) b jets • Form the top withone b jet + 2 non-b jets left, lepton charge gives the opposite sign of the top

  13. Methodadopted • In this talk : • Review of lepton selectionefficiency • Major backgrounds discussed : ZWW, ttbbqqτv • Full study for later : • Hadronic top (not checkedyet) • Add all other backgrounds (purity) • Report on systematics of the observables

  14. Identification of leptons Isolation Efficiencies and purities of the selected lepton Efficiencies : angular and energetic 3. Efficiencies

  15. Indentification of leptons • Ratherloosecuts : • Muon oftenpicks a small pion cluster in the calorimeters • Same for electron / photon • Impose isolation criteria for lepton insideits jet

  16. Isolation • In reconstructedevents, look at the true (MC) lepton : • Events forced to 4 jets • ttbbqqlv : 4 jets + 1 lepton • Define : • z = Elepton/Eclosest jet • pT in the closest jet • Lepton is : • Leading (high z) • Or isolated (highpT) • Not leading or isolated O(1%) True lepton embeddedinside a jet

  17. Isolation • Sameview for identified leptons (muons here) • Isolation criteria : (rejects BlvX, • + highest z and mis-ids) (if Nleptons>1) Remark : studydonewithperfecttracking best efficiencyachievable

  18. Efficiencies and purities of the lepton • Trackinginefficiencies : • Muon = 94.4 % - 92.6 % = 1.8 % (|cos θ|>0.97) • Electron = 93.5 % - 87.7 % = 5.8 % (TPC disk,|cos θ|>0.97)

  19. Efficiencies : angular and energetic • Effienciesunder control : • Trackingworseat large angles and in the TPC disk • Leptons withsmallenergies are suppressed by isolation

  20. Results Cross section and ALR Conclusions and prospects 4. Results

  21. Results • Simulation donewith full e+e- polarisation i.e. P(e+e-)=(±1, ±1)  P(e+e-)=(±30%, ±80%) • ZWW isverysmall ( < 1%) : • canbemeasured : veto on b (Z  uu, dd, ss, cc) • and substracted • Comment on ttbbqqτv : • Lepton of τlvvdecayreconstructed ( ≈ 35% of τevents) • Addsstatistics for σ(tt), ALRand AFB (wherehadronic top direction willbereconstructed)

  22. Cross-section and ALR • σ = N/(εL), L = 500fb-1 • σ(ttSL)unpol. = 159.4 fb, Δσ/σ = 0.37% (stat.) • Whizard : σ(ttSL)unpol. = 159.6 fb (-0.1%) • P(e+e-)= (±30%, ±80%)  Δσ/σ= 0.28%/0.42% (stat.) • ALR = 0.435, ΔALR/ALR = 0.54% (stat.) • ALR = 0.37 expected… Whizardproblem ? • However, interest lies in relative uncertainty • P(e+e-)= (±30%, ±80%)  ΔALR/ALR= 0.69% (stat.)

  23. Conclusion and prospects • To find a lepton (e,µ) in a semileptonicenvironmentefficiency > 88% , purity > 98% • Major backgrounds seemunder control (ZWW and ttbbqqτv) • Furtherchecks of backgrounds e.g. top full hadronicdecaysneeded • σ and ALRcanbeknownat 0.4% and 0.7% statisticaluncertainty (systematicsguaranteedsmall due to large purity) • One stepbeyond : reconstruct the hadronic top quark to measure AFB, mtop • Next : add background and check purity (cutbasedanalysisforeseen)

  24. Extractefficiency and purity of the selected lepton Addingelectrons and muons Top physics : LHC and ILC Angular distribution : top vs lepton Finding ZWW in bbqqlvevents Comparative distributions ZWW/tt Semileptonic taus : tt  bbqqτv Full hadronic tops Top couplings : bibliography 5. Additionalmaterial

  25. Extractefficiency and purity of the selected lepton • Count number of selected leptons with the previouscriteria (atreconstructedlevel) • Wedefinex = Proba of good lepton choseny = Proba of mis-id. • How to migrate ? • Highest z : 90.7 % good • x = 92.6% • y = 6.9 % • After migration : 1.2 % of bad muons x(1-y)+ y(1-x) Negligible (1-x)(1-y) xy

  26. Addingelectrons and muons • Now : takeanykind of lepton • highest z candidate amongindentified muons and electrons • Efficiencyexpectedhigher, but purityshoulddecrease

  27. LC 1 pb, LHC 1nb but for gluon couplings only Very good s/b at ILC and energy/momentum conservation allows to reconstruct modes with a neutrino Mt and Gt with ≈50 MeV error, 0.4% on cross section LC unique to measure tR and tL Z couplings at % (ND>4) LHC > 10 times worse Top physics : LHC and ILC ILD

  28. Angular distribution : top vs lepton • For P(e-) = +1 (e-R) : correlationbetween directions of the lepton and its top • For P(e-) = -1 (e-L) : anticorrelation

  29. Finding ZWW in bbqqlvevents • Using the MC table of bbqqlv, t1 = blv (top lepton) and t2 = bqq (top jet) are reconstructed • Tag : top or ZWW • Top eventistagged if oror • Check on Mbb Z peak in ZWW events, < 2%

  30. Comparative distributions : ZWW/tt • At MC level, top and ZWW events are separated • Lepton distributions : • Angular • Energetic • ZWW clearlynegligible • Needs to besubstracted to reachpermilprecision

  31. Semileptonic taus : tt  bbqqτv • A lepton isfound in 1/3 of semileptonic tau events • Addsstatistics for measurements but cannot use lepton

  32. Full hadronic tops • Ycutexpected to beenough to separatesemileptonic tops fromhadronicones… Maybe not enough. Try y56.

  33. Top couplings : bibliography • [1] : Djouadi et al., NuclearPhysics B, Volume 773, Issues 1-2, 25 June 2007, Pages 43-64 • [2] : Hosotani et al., Prog. Theor. Phys. 123 (2010), 757-790 • [3] : Cui, Gherghetta et al., arXiv:1006.3322v1 [hep-ph] • [4] : Carena et al., Nuclear Physics BVolume 759, Issues 1-2, 18 December 2006, Pages 202-227

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