1. Resolved ttbar analysis status
Thijs Cornelissen (Wuppertal)

2. 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

3. 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%

4. Event yields, electron

5. Event yields, muons

6. 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

7. 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

8. 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

9. 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