Resolved ttbar analysis status Thijs Cornelissen (Wuppertal)

Introduction Aim of resolved analysis is to reconstruct ttbar system with standard antiKt4 jets 4 jets, lepton, missing ET Rel. 17 resolved ttbar analysis brings several improvements compared to Rel. 16: New lepton isolation ‘mini isolation’ JVF (‘jet vertex fraction’) cut on jets JVF is pT weighted fraction of tracks in jet that are compatible with primary vertex Wuppertal involvement in Rel. 17 analysis: Cut flows, event yields QCD fit

Cut flows Cut flow with standard ttbar selection was validated early February Despite this, cut flow exercises in resonance analysis dragged on for a long time Selection was frozen very late (around ICHEP) New recipes and scale factors take time to implement and debug between groups (mini isolation in particular) Some prescriptions by top reco group ambiguous or inconsistent, missing ET in particular My production suffered from missing/incomplete/wrong versions of runs Central D3PD production contained duplicate runs, IMO very confusing Overall, my take is there were too many people/groups trying to reach agreement on too many different versions of the cut flow Status of cut flow itself (next slides): data OK (slightly larger differences with electrons than in muons), ttbar shows differences ~2%

Event yields, electron

Event yields, muons

Lepton isolation Standard isolation criteria do not work in highly boosted events E.g. standard muon isolation prescription only ~50% efficient in Z’ 2 TeV events Track based relative isolation already performs much better, ~90% efficient Choice was to use new ‘mini isolation’ which is even more efficient, ~95% Track based relative isolation with pT dependent cone size: DR=10 GeV / pT muons electrons

Ttbar reconstruction Two methods to reconstruct ttbar system in resolved analysis: dRmin and c2 dRmin starts with four hardest jets, tries to remove jets from ISR/FSR by cutting on dR to closest jet c2 method uses W and top mass constraints to select right combinations of jets Both methods still used in Rel. 17 analysis In Rel. 16 analysis, dRmin method was preferred because it showed less pileup dependence In Rel. 17 analysis, c2 gives slightly better expected limits c2 drmin

Systematics Some systematics are strongly constrained by data (error apparently overestimated): JES, JVF, QCD normalization List of systematics so long (16 NP in JES alone) that limit setting cannot handle it anymore Limits now based on reduced list: no lepton systematics, reduced JES

Conclusions Resolved analysis now in good shape Expected limit around 1.7 TeV for leptophobic Z’ Previous limits: 860 GeV (resolved, 2 fb-1), 1.15 TeV (boosted, 2 fb-1) Improved limit due to more data, but also improvements in analysis (lepton isolation in particular) Analysis missed ICHEP, now on critical path for TOP2012 Latest schedule: unblind ~now, circulate internal note 20/8, WG approval 23/8