Also use VBF jets to compute the PU jet ID sF

[ktht]

Before it slips off from my mind: need to include preselected VBF jets when computing the PU jet ID SF. Although it's a bit of an open item as to which jet collection should we use:

1. VBF jets that pass just the preselection;
2. VBF jets that pass the preselection and are cleaned wrt leptons;
3. VBF jets that pass the preselection, and are cleaned wrt leptons and other jets.

I think that 2. is the most accurate choice here because it would be more-or-less on the same footing with the cuts that the central jets are required to pass when entering the SF calculation.

[ktht]

Regarding VBF jets, I think there's a bug in SL channel. Here the VBF jets are cleaned wrt the W->jj jets as identified by the JPA:

hh-bbww/bin/analyze2_hh_bb1l.cc

Line 1948 in e150814

cleanedJetsAK4_vbf = jetCleanerAK4_dR08(cleanedJetsAK4_wrtHbb, overlaps);

The AK4 jets that are cleaned wrt the selected H->bb AK8 jet is done here:

hh-bbww/bin/analyze2_hh_bb1l.cc

Line 1698 in e150814

cleanedJetsAK4_wrtHbb = jetCleanerAK4_dR12(selJetsAK4, std::vector<const RecoJetBase*>({ selJetAK8_Hbb }));

But the jets that enter the cleaning are central jets:

hh-bbww/bin/analyze2_hh_bb1l.cc

Line 1314 in e150814

const std::vector<const RecoJet*> selJetsAK4 = jetSelectorAK4_wPileupJetId(cleanedJetsAK4_wrtLeptons, isHigherPt);

I believe this is by a mistake. I'll reorganize the code a bit because in the synchronization we agreed to record the number of VBF jets:

• after the selection;
• after the selection and cleaning wrt the fakeable leptons,
• after the selection, cleaning wrt the fakeable leptons, and wrt other jets.

[veelken]

Hi Karl,

sorry, I don't understand where you see a problem. The AK4 jets that are selected by the JPA are central AK4 jets (|eta| < 2.4). The VBF jets are cleaned wrt the AK4 jets selected by the JPA in these lines:

hh-bbww/bin/analyze2_hh_bb1l.cc

Lines 1942 to 1957 in e150814

	// select VBF jet candidates
	std::vector<const RecoJet*> cleanedJetsAK4_vbf;
	if ( selJetAK8_Hbb ) {
	std::vector<const RecoJetBase*> overlaps;
	if ( selJet1_Wjj ) overlaps.push_back(selJet1_Wjj);
	if ( selJet2_Wjj ) overlaps.push_back(selJet2_Wjj);
	cleanedJetsAK4_vbf = jetCleanerAK4_dR08(cleanedJetsAK4_wrtHbb, overlaps);
	} else {
	std::vector<const RecoJetBase*> overlaps;
	if ( selJet1_Hbb ) overlaps.push_back(selJet1_Hbb);
	if ( selJet2_Hbb ) overlaps.push_back(selJet2_Hbb);
	if ( selJet1_Wjj ) overlaps.push_back(selJet1_Wjj);
	if ( selJet2_Wjj ) overlaps.push_back(selJet2_Wjj);
	cleanedJetsAK4_vbf = jetCleanerAK4_dR08(cleanedJetsAK4_wrtLeptons, overlaps);
	}
	const std::vector<const RecoJet*> selJetsAK4_vbf = jetSelectorAK4_vbf(cleanedJetsAK4_vbf, isHigherPt);

This looks correct to me.

[ktht]

This part is ok, the problem I think is that cleanedJetsAK4_wrtHbb originates from

hh-bbww/bin/analyze2_hh_bb1l.cc

Line 1698 in e150814

cleanedJetsAK4_wrtHbb = jetCleanerAK4_dR12(selJetsAK4, std::vector<const RecoJetBase*>({ selJetAK8_Hbb }));

where selJetsAK4 are defined here:

hh-bbww/bin/analyze2_hh_bb1l.cc

Line 1314 in e150814

const std::vector<const RecoJet*> selJetsAK4 = jetSelectorAK4_wPileupJetId(cleanedJetsAK4_wrtLeptons, isHigherPt);

The jetSelectorAK4_wPileupJetId selector does not include jets beyond the acceptance region:

hh-bbww/bin/analyze2_hh_bb1l.cc

Lines 644 to 645 in e150814

	RecoJetCollectionSelector jetSelectorAK4_wPileupJetId(era, -1, isDEBUG);
	jetSelectorAK4_wPileupJetId.getSelector().set_pileupJetId(apply_pileupJetID);

So, if I'm reading the code correctly, it only considers central jets as the VBF jets in the boosted category.

[ktht]

The pT cut on VBF jets was set to 30 GeV in commit 8d614f1 but there is no explanation why the pT cut was raised:

hh-bbww/bin/analyze2_hh_bb2l.cc

Line 650 in e150814

jetSelectorAK4_vbf.getSelector().set_min_pt(30.);

Was this cut taken from bbtautau analysis, maybe?

In any case, the pT cut in our gitlab is still at 25 GeV, so I'll change it back to 25 in my PR, too. Other groups have already synchronized in the VBF jet variables, but we're not.

edit: indeed, the pT > 30 GeV cut was mentioned in bbtautau AN (AN2018/121v4, L291)

[veelken]

Hi Karl,

the VBF jet pT > 30 GeV cut was indeed taken from the HH->bbtautau analysis (cf. slide 5 of https://indico.cern.ch/event/963619/contributions/4118889/attachments/2149275/3623492/statusReport_24_11_2020.pdf ). I would prefer if we keep using the 30 GeV cut for VBF jets, if we can convince the Aachen and Louvain groups to switch to 30 GeV, for two reasons:

1. It will make the documentation and combination of datacards easier if we use the same VBF jet cuts as the HH->bbtautau analysis
2. The VBF jets are reconstructed outside of the tracking acceptance, so are more affected by pileup and potential miscalibration and/or noise of the calorimeters. My understanding is that the official JetMET recommendation is to use jets of pT > 30 GeV (for b-jets/jets within the tracking acceptance, we get permission to reduce the pT threshold to 25 GeV, because central jets depend more on the track reconstruction and are less affected by pileup and potential miscalibration and/or noise of the calorimeters)

[ktht]

Thank you, Christian. I had no strong preference before because we already apply PU jet ID cut also on the VBF jets, so reducing the pT cut by 5 GeV shouldn't make much difference. But I take your point that it's best to keep the common definitions across different HH analyses as similar as possible. I'll let the other groups know that we should use pT > 30 GeV cut for the VBF jets.