First attempt at reweighting Powheg+Pythia → Powheg+Herwig in W→μν events

2 Statistics ● AOD/D3PD statistics for W → μ -- ν: ● Powheg+Pythia: 17M ● Powheg+Herwig: 3M ● Much smaller statistics in secondary samples hurts the uncertainty on C_W ● Powheg+Herwig EVGEN sample = 17M ● Can we reweight Powheg+Pythia to Powheg+Herwig at EVGEN level, and then use “reweighted” Powheg+Pythia instead? ● First try today: 2D reweighting in mu_p T x nu_p T

3 mu_pT nu_pT Scale factor to convert Powheg+Pythia → Powheg+Herwig 1D version of the scale factor: mu_pT Note that the scale factor spans the entire phase space (not just fiducial)

4 First test: looking at truth-level, fiducial region What's going on here? The “Powheg+Pythia(reweighted)” looks nothing like Powheg+Herwig, while the default Powheg+Pythia is almost exactly the same? Explanation: ah, but we apply W p T reweighting, which brings Powheg+Pythia and Powheg+Herwig into a good agreement without the need for extra kinematic reweighting mu_pT Black = Powheg+Herwig Red = Powheg+Pythia Green = Powheg+Pythia(reweighted) Ratios of Powheg+Pythia and Powheg+Pythia(reweighted) to Powheg+Herwig

5 First test: looking at truth-level, fiducial region, NOT using W p T reweighting We see here that if W pT reweighting is NOT applied, then the default Powheg+Pythia differs from Powheg+Herwig. In that case, kinematic mu_pt x nu_pt improves agreement. For the next few slides, I disable W p T reweighting. mu_pT Black = Powheg+Herwig Red = Powheg+Pythia Green = Powheg+Pythia(reweighted) Ratios of Powheg+Pythia and Powheg+Pythia(reweighted) to Powheg+Herwig

6 Lepton p T and neutrino p T at truth-level, fiducial region mu_p T nu_p T At truth-level, Powheg+Pythia(reweighted) and Powheg+Herwig look similar. What about detector level? Muon pT (same plot as last slide)Neutrino pT

7 Lepton p T and neutrino p T at reco- level mu_p T MET At reco-level, Powheg+Pythia(reweighted) and Powheg+Herwig still have similar muon p T spectra. But MET shows ~2% disagreement around the 25 GeV cut. This is despite the fact that neutrino p T is compatible at truth level. Muon pT (same plot as last slide)Neutrino pT

8 Effect on C_W ● What this all means for C_W factors: – Here, W p T reweighting is NOT applied ● Powheg+Herwig = ± 0.04 % ● Powheg+Pythia = ± 0.02 % ● Powheg+Pythia(reweighted) = ± 0.02 % ● EVGEN-level kinematic reweighting only slightly improves the agreement in C_W ● Still large residual difference, perhaps due to reco-level MET difference between Pythia and Herwig?

9 ONE LAST TRY ● What if we try to reweight based on Truth_MET, rather than neutrino momentum? ● The hope is that differences due to hadronization between Pythia and Powheg are reflected already at the level of Truth_MET

10 TRUTH_MET: definitions I tried reweighting with two definitions: Definition 1: NonInt Definition 2: (Int + Muons)

11 MET at reco-level mu_p T MET Conclusions: even if reweighting is based on Truth_MET, the reco-level spectra are still deferent between Powheg+Pythia and Powheg+Herwig, MET, reweighting via Truth_MET definition 2MET, reweighting via Truth_MET definition 1