Top studies Philippe Doublet Thibault Frisson, Roman Pöschl, François Richard Réunion de groupe ILC - LAL - 22/02/2011

Introduction : why top ? Top : – known particle, – heaviest SM fermion (EWSB connections)  extra-dimensions – detector challenges  b-tagging, jets, lepton tracking… tb W +  b l + v = 1b jet + 1 top-like-sign lepton ILC, 500 GeV We study : semileptonic top decays, i.e. tt  bWbW  b(lv)b(qq) Signature = 4 jets (2 b) + 1 lepton Direct decay : no hadronisation  b qq = 1b jet + 2 light jets from a W

A hint of theory : extra-dimensions Higgs on IR brane for gauge hierarchy problem SM fermions have different locations along the 5th dimension Fermion-boson couplings = wavefunctions overlaps Overlaps leptons – Higgs in the 5th dimension generate good Yukawa couplings with O(1) localisation parameters tR0tR0 e0e0 Aµ0Aµ0 H y (5th dim.) 0πRπR UV brane (M Pl ) IR brane (TeV) bulk Aµ1Aµ1 u0u0

Aim : measure t R and t L couplings L/R couplings affected by localisation on the brane via Z-Z’ mixing Δg(t R )/g(t R ) Δg(t L )/g(t L ) SM 0,0 Djouadi -34%,-1% Hosotani +18%,-7% Gherghetta -20%,-20% Carena 0,-20% Observables connected to g(t R ) and g(t L ) ?  A LR and A FB

A LR and A FB Definitions : A LR = (polar. flip) A FB = (direction) Error : ΔA = Conclusion : only need to count top events for A LR Corollary : Reconstruct at most 1 top direction for A FB tt  {bW}{bW}  {b(lv)}{b(qq)} : reconstruct the hadronic top

Semileptonic channel Clean and easy signature : 1 lepton + at least 1 b jet – Remark : lepton = e/µ and τ  e/µ adds statistics Backgrounds ? – Worst : ZWW (Z  bb) but under control (MC level) – Hadronic top (bbqqqq): needs to be done – All the rest should be fine σ(tt) ≈ 600 fb at 500 GeV (≈ 180 fb for SL top into e and µ) ZWW (Z  bb) ≈ 8 fb ZWW/top separation at MC level

Lepton finding : method 1.Topology forced to 4 jets  the lepton is embedded in one jet 2.Check all leptons in jets (  lepton id.) 3.Ours is either leading or isolated in its closest jet (  cuts) Case 1 : leadingCase 2 : isolated

Lepton finding : efficiencies and purities Tracking inefficiencies : Muon = 94.4 % % = 1.8 % (|cos θ|>0.97) Electron = 93.5 % % = 5.8 % (TPC disk,|cos θ|>0.97) ParticleEfficiencyBad leptonPurity Muon93.6%2.9%97.1% Electron89.7%3.9%96.1%

Efficiencies : angular and energetic Effiencies under control : – Tracking worse at large angles and in the TPC disk – Leptons with small energies are suppressed by isolation cuts

B-tagging on top events We require to find 1 b jet, highest btag > 0.5 One b found  comes with a second b Jet with the highest B tag among the 4 Real B jet Light jet (negligible) Btag > 0.5 : Purity = 98% Efficiency = 91% 0.5 Excellent angular coverage (for the best B jet)

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

A look at reconstructed tops 2 b jets + 2 light jets ( = W ) Keep top closest to : – E top = 250 GeV and M top = 172 GeV Only 2 possible combinations for the top = (b 1 W) or (b 2 W) Reconstructed mass without effort (not our goal), just a cross-check An idea of top direction… (P e- = +100%) ALR = – 0.41 expected… Whizardise…

Conclusion and perspectives Measurement of top asymetries in the semileptonic channel – Lepton and first B jet very efficient and pure – τ channel helps with statistics – Check full hadronic top Need to look further into top reconstruction Use angular distributions of leptons for CPV and complementary studies Réunion de groupe ILC - LAL - 22/02/2011