Top Quark Asymmetries Measurement at ILC - Research Insights
Explore the asymmetries of the top quark at the International Linear Collider (ILC) through detailed measurements and analyses presented at the LCWS Granada conference in September 2011 by Philippe Doublet and team. Discover intriguing findings related to the top quark, flavor hierarchy, and Randall-Sundrum models. Gain insights into the measurement methods and motivations guiding this cutting-edge research.
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Measuring the asymmetries of the top quark at the ILC Philippe Doublet Roman P schl, Fran ois Richard + Thibault Frisson & J r my Rouene LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Plan 1. Motivation 2. Measurement method 3. Efficiencies 4. Results LCWS Granada, Sept. 2011 Philippe Doublet - LAL
The top quark and flavor hierarchy Geography in Randall-Sundrum models Top to Z couplings 1. MOTIVATION LCWS Granada, Sept. 2011 Philippe Doublet - LAL
The top quark and flavor hierarchy Flavor hierarchy ? Role of 3rd generation ? Top quark : no hadronisation clean and detailed observations Redo measurements of ALRand AFBwith the top LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Geography in Randall-Sundrum models e0 IR brane (TeV) UV brane (MPl) 0 t b H A 0 t0R L bulk y (5th dim.) 0 R Higgs on IR brane for gauge hierarchy problem SM fermions have different locations along the 5th dimension Overlaps leptons Higgs in the 5th dimension generate good Yukawa couplings with O(1) localisation parameters LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Top to Z couplings Several RS models predict modified left gZ(tL) and right gZ(tR) top couplings to Z (Z-ZKK mixing, ) g(tL)/g(tL) g(tR)/g(tR) SM 0,0 Djouadi [1] -34%,-1% Hosotani [2] +18%,-7% Carena [4] 0,-20% Gherghetta [3] -20%,-20% LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Observables Top quark cross section Measurement with the ILD detector Reconstruction within the ILD framework Requirements 2. MEASUREMENT METHOD LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Observables L R ( ) ( ) N e N e top top (tt), ALR and AFB : ALR= (e-polar flip) L R + ( ) ( ) N e N e top top (cos ) 0 (cos ) 0 N N top top AFB= (top direction) + (cos ) 0 (cos ) 0 N N top top Semileptonic decay mode : tt (bW)(bW) (bqq)(blv) Gives top charge l = e, Allows reconstruction of the top quark From ALR and AFB, one deduces gZ(tL) and gZ(tR) couplings LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Top quark cross section (tt) 600 fb at 500 GeV with 500 fb-1 Ntotal ~ 570k events Semileptonic ~ 34% Almost background free ? Major background = other top channels find 1 isolated lepton WW no b quark bb simple topology Major background : ZWW (Z bb) 8 fb, same topology Small but needs to be subtracted 500 Process tt bb WW ZZ ZWW Philippe Doublet - LAL ALR(%) 36.7 62.9 98.8 31.0 89 LCWS Granada, Sept. 2011
Measurement with the ILD detector ILD optimised for Particle Flow technique (i.e. reconstruct every particle in a jet) 3.5 T B-field Performances : Vertexing : IP = 5 m (+) 10 m/p(GeV)sin3/2 Tracking : (1/pT) < 5.10-5 GeV-1 Granular calorimetry : E/E ~ 30%/ E LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Reconstruction whithin the ILD framework Full simulation is done with the ILD detector under GEANT4 (Mokka software) Objects reconstructed with Particle Flow algorithm (Pandora) Data used : samples prepared for the LOIs LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Requirements 2 light quarks = W Hadronic top to reconstruct b tt bbqqlv (l=e, ) Need at least 1 b jet (vertex) Find 1 lepton (tracking) Method : Find a lepton Force 4 jets clustering Find at least 1 (or 2) b jets Form the top with one b jet + 2 non-b jets left, lepton charge gives the opposite sign of the top e- e+ anti top b neutrino isolated lepton gives top charge LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Identification of leptons Isolation Efficiencies and purities of the selected lepton Efficiencies : angular and energetic B tagging 3. EFFICIENCIES LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Isolation In reconstructed events, look at the true (MC) lepton : Events forced to 4 jets tt bbqqlv : 4 jets + 1 lepton Define : z = Elepton/Ejet xT = pT/Mjet Lepton is : 1. Leading (high z) 2. At high pT 3. Not isolated optimise cuts on z and xT True lepton embedded inside a jet LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Results of isolation cuts Leading Red = leptons in semileptonic top events Large pT Blue = leptons in full hadronic top events = leptons from b 0.6 Cut here Kinematic limit of pT = Mjet/2 0.25 Not isolated (lepton from b) LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Efficiencies : angular and energetic Good efficiency with ~ full angular coverage Effiencies under control : Tracking worse in very forward regions Leptons with small energies are suppressed by isolation cuts Efficiency = 87.9% Contamination = 0.3% LCWS Granada, Sept. 2011 Philippe Doublet - LAL
B tagging Vertex detector measure offset, multiplicity and mass of jets to separate b from c decays B Good angular coverage Interaction point 4 jets 2 highest Btag = b1 & b2 2 light jets = W Limitation of B tagging = B decay length LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Top reconstruction Cross section and ALR Problem with the top reconstruction Origin of the problem Precisions reached Conclusions and prospects 4. RESULTS LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Top reconstruction 2 top candidates : (b1+ W) or (b2+ W) Retain candidate with minimal d = (Mcand-Mt) / mt + (Ecand-Ebeam) / Et + (MWrec-MW) / mw W = 4.2 GeV t = 7.1 GeV ~ 25 MeV precision on Mt LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Cross-section and ALR = N/( L), L = 500fb-1 After background suppression : Efficiency = 72.7 % + Contamination = 4.6 % (mostly full hadronic top pairs) (tt SL)unpol. = 159.4 fb Whizard : (tt SL)unpol. = 159.6 fb (-0.1%) P(e-e+)= ( 80%, 0) / = 0.39% (stat.) ALR = 0.435 ALR = 0.37 expected Whizard problem ? However, interest lies in relative uncertainty P(e-e+)= ( 80%, 0) ALR/ALR = 1.24% (stat.) LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Problem with the top reconstruction Angular distributions for e-Land e-Revents No migration ? Relative errors : -5.2% (AFBtR) -40.4 % (AFBtL) 1.1 % (stat.) LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Solving the problem d = (Mcand-Mt) / mt + (Ecand-Ebeam) / Et + (MWrec-MW) / mw quality of the candidate 1. Is it due to the reconstruction ? Cut on the quality of the candidate (particle flow) Efficiency in e-L: x60% relative systematics : 40% 20 % 2. Is is intrinsic ? Effect of helicity structure of the decays Ambiguous solutions Seen with partonic reco. parton limit LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Precisions reached Correction on AFBtL= dominant systematic (reco. + intrinsic) - Good PFA + b tagging are essential - 20% correction on AFBtLcan be done on a well tuned MC AFBtR AFBtL QZtL QZtR Pe-/ Pe+ (80% / 0) ALR stat. error 1.3% 1.2 % 1.4 % 1.0 % 1.9 % Possible to probe some RS models with MKK~ 2.8 TeV up to 25 TeV LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Conclusion and prospects Impact of detector & reconstruction performances on a complex channel : lepton + 4 jets with 2 b jets Final efficiency = 72.7% Contamination = 4.6% (Major backgrounds are other top channels) and ALRcan be known at 0.4% and 1.3% statistical uncertainty (systematics guaranteed small due to large purity) Problem in reconstructing the direction of the top Reconstruction needs improvements or leads to efficiency losses Intrinsic problem with AFBtLneeds excellent Monte Carlo AFBtR/Lknown with 1.2/1.4% statistical uncertainty Study of AFBto enter the DBD for the ILD in 2012 LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Top physics : LHC and ILC Top couplings : bibliography 5. ADDITIONAL MATERIAL LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Top physics : LHC and ILC 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 t with 50 MeV error, 0.4% on cross section LC unique to measure tRand tLZ couplings at % (ND>4) LHC > 10 times worse ILD LOI LCWS Granada, Sept. 2011 Philippe Doublet - LAL
Top couplings : bibliography [1] : Djouadi et al., Nuclear Physics 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 B Volume 759, Issues 1-2, 18 December 2006, Pages 202-227 LCWS Granada, Sept. 2011 Philippe Doublet - LAL
