Diphoton+MET: Z( ) Cross Section

1. Diphoton+MET: Z() Cross Section Max Baugh, Ryan Reece, Bruce Schumm SCIPP 15 May 2017

2. ISSUE • Z background contributions are small; we have always estimated them directly from MC • Z simulated with SHERPA MC  Leading order + parton-shower corrections • Nominal Cross section taken from metadata • There exists an NLO calculation (Bozzi et al., arXiv:1107.3149v1 [hep-ph]) with theoretically controlled uncertainties • Project: Compare total cross sections from Bozzi and Sherpa and come to some conclusion or other

3. FURTHER ISSUE • SHERPA sample generated at 13 TeV with certain cuts • Bozzi calculation for 14 TeV with other cuts • Biggest difference is photon pT cut (30 GeV for Bozzi and 50 GeV for SHERPA), then beam energy • Must figure out a way to compare apples to apples • Approach: Use MadGraph to reproduce Bozzi, then change MadGraph cuts to compare to SHERPA and hope for agreement. • We don’t see agreement (and we didn’t in Run I either; too small to worry about for our strong production 2015 analysis)

4. MadGraph vs. Bozzi Thanks to UCSC grad Max Baugh for doing the work (will include him on the Note) Cuts used in 14 TeVBozzi calculation: • pT,> 30 GeV; || < 2.5 • R > 0.4 • Various parton-photon separation cuts that shouldn’t make any difference at leading order (and seem not to) Results for total Leading Order Z(ll) cross section, per species l of neutrino: ~5% agreement

5. Now apply SHERPA cuts to MadGraph Cuts used in 13 TeV SHERPA generation: • pT,> 50 GeV; || < 9999. • R > 0.2 • M > 10 GeV • “Photon isolation cut” Apply cuts in black to 13 TeV Z() MadGraph calculation (couldn’t figure out how to easily apply green cuts, but note that those would lower the MadGraph result further. (Again, per neutrino species)

6. Compare Bozzi to Sherpa via MadGraph Cuts used in 13 TeV SHERPA generation: • pT,> 50 GeV; || < 9999. • R > 0.2 • M > 10 GeV • “Photon isolation cut” Apply cuts in black to 13 TeV Z() MadGraph calculation (couldn’t figure out how to easily apply green cuts, but note that those would lower the MadGraph result further. (Again, per neutrino species)

7. Another Note Compare W(e) to Z() at next-to-leading order (Bozzi vs. Bozzi), for 30 GeV pT cut • Again, per lepton species • Direct from paper; no need for MadGraph • Full NLO calculation • For the W background, we have a confirming control region  Naively, we expect Z to be significantly smaller than W

8. NOT YET!!

9. The Gluino-Bino Grid

10. New: minimum background uncertainty of b = 0.2 events

11. Optimization: (mgluino,mbino) = (1500,100)

12. Optimization: (mgluino,mbino) = (1500,1300)

13. Optimization Results Results suggest single SR with the following selection cuts: • pT > 75 GeV • (jet,MET) > 0.5 • Etmiss > 175 GeV • Meff > 1500 GeV Relative to the 8 TeV analysis, we have • Introduced background uncertainty in the optimization • Have x10 less luminosity This seems to lessen emphasis on ultra-low background, lead to optimization point that is very inclusive of the signal, de-emphasizing the differences between the two focus points.

14. Background Estimation • EW (e  ) Background • e   fake rate estimation • QCD (jet  ) Background • Irreducible Background • Wgg (via control sample) • Zgg (via Sherpa normalized to Bozzi et al)

15. e   Fake Rate Slightly new approach: no distinction between “tag” and “probe”; instead, just look at ee and e pairs within the Z mass region Consider both electron and photon objects down to 25 GeV ee e

16. e   Fake Rate Continued • Form 2D grids in , pT • Two entries for ee events; only photon for e events • Ratio of grids gives fake rate as a function of , pT • Have required e+e- to be back-to-back; may limit pT reach of study • Are looking into removing this requirement

18. QCD Background Estimate • Old approach: • “Data” in above plot is pseudophoton control sample •  is from MC • Use MET shape of pseudophoton sample, after subtracting off  contribution, to estimate QCD background

19. Approach: “ABCD” Method for jet Fakes • Real diphoton background from  MC, scaled to get correct MET shape for MET < 100 GeV • Jet   contribution from date-driven fake factor via “ABCD” method Pseudo-photon selection from monophoton analysis Fake factor definitions

20. Nominal QCD Model • Scale isolated pseudophotons with Fake Factor • Real diphoton contribution directly from SHERPA  Force MET agreement by re-weighting in MET, 0 < MET < 100.

21. Diphoton Scale Factors • Normalize in range 0 < MET < 100; use number from last bin for MET > 100 • Validation Region 100 < MET < 175 • Signal Region MET > 175

22. QCD Model After Reweighting • Agreement maintained in M_eff

23. QCD Background: 2 Approaches Approach 2 Relax Meff cut to 700 GeV • 8% of events above MET > 175 For Meff > 1500, 0.20.2 events for any MET. If uncorrelated, Nfake = 0.020.02 events Approach 1 See 0 events in SR from either diphoton MC (real diphoton) or isolated pseudophotons (jet fakes) Scale Poisson 68% UL (1.14 events) by lum*reweight or fake rate Nreal < 0.01 events Nfake < 0.25 events Concerns about MET/Meff and Isolation/ID correlations • Be conservative • NQCD = 0.05+0.20-0.05 events

24. W Control Sample

25. W Control Sample

26. Other Measurements of W Production From the SM Group:

27. Z Background Estimated directly with SHERPA MC Yield in signal region is 0.02 events Not really susceptible to systematic concerns; just say NZ = 0.02  0.02 events

28. Overall Background Estimate

29. Summary/Outlook Still working on one or two small refinements • Impose diphoton trigger on Z sample used for electron->photon fake-rate estimate, and require medium rather than tight electron • Compare SHERPA MC to Madgraph to possibly reduce Z background uncertainty (but is already negligible) • Fix holes in documentation Moving on to evaluating signal systematics and limit-setting formalism Essentially ready to request unblinding approval

30. Monophoton Pseudophoton Def’n