Diphoton+MET 2015: Overview of Path towards First Results

1. Diphoton+MET 2015: Overview of Path towards First Results A living document… Bruce Schumm SCIPP 18 May 2015

2. Timelines I • Is this still the best guess? • 50 nsec running • Few pb-1 by end of May (but trigger in commissioning) • As much as 1 fb-1 by end of June • 2-3 fb-1 by end of August • can use for CONF NOTE • 25 nsec running • 10 fb-1 end of October • For journal publication • Proposal: Push/optimize for 2-3 fb-1 result

3. Timelines II • If we push for “August” result… • Analysis walkthrough beginning of June • ~2 Hr process, with much discussion • Expected to present unblinding case during walkthrough, up to necessary lacunae associated with data-driven studies • Editorial Board formed at that point • Draft of support note expected at that point •  Seems unlikely. Grids probably not event ready. Instead just present status

4. Tasks Overview • Code/Infrastructure [Some done] • xAOD • Derivations • Higher-level infrastructure (Ryan’s package) • Events variables (MET with photons, etc.) • Event selection • Preliminary studies • Optimization • Backgrounds • QCD • Electroweak • Irreducible • Overlap (?) • Models [Largely done] • SM samples • Strong & EW signal • Full vs. fast sim?

5. Models • SM samples defined; generation underway. Much overlap with other groups; much hard work by Milano group! • Gluino, wino grids defined • All BF and decay length issues resolved • Fast Sim sufficiently validated • Of order ~2m events at 10K/point, more or less approved • Final validation step (generator-level filter to ensure two binos in each event) underway • Need this soon! (optimization)

6. Gluino-Bino Grid (not quite final version)

7. Wino-Bino Grid (also not quite final)

8. Backgrounds - QCD • Prior approach was to assume real diphotons are 7525% of low-MET background • Diphoton MC used to estimate high-MET contribution • Pseudophoton control sample scaled to remainder of low-MET events used to estimate -jet contribution • Using 8 TeV data to explore new approach (ABCD method with pseudophotons and relaxed isolation); preliminary results expected soon • If this doesn’t work, will need to fall back to old pseudophoton control-sample technique

9. Backgrounds - EW • Estimate with e control sample scaled by e fake rate • Need to select e control sample • Tag&probe study of e fake rate underway [Giacomo] MAYBE: • W MC suggests that ~25% of EW background doesn’t arise from e fakes • Some of this may be accounted for in QCD background • Some of QCD background may include e fake events • Prior approach was to include 25% systematic error on the EW background • Perform QCD/EW background overlap study?

10. Backgrounds - Irreducible • W contribution estimated via l control sample and simultaneous fit with SR • Question about comparison w/ VBFNLO expectation • Need to develop control sample and explore • Z contribution from Sherpa, scaled to VBFNLO (via MadGraph) in relevant kinematic region • Big difference between VBFNLO and Sherpa not understood (Sherpa much larger) • Need to revisit

11. TASKS POTENTIALLY COMMON TO ALL GROUPS SM MC samples xAOD framework issues (not completely sure what I mean by this…) Code snippets reflecting agreed-upon object definitions Isolation variable code Pseudophoton object definition code e->gamma fake rate study dPhi studies (one-sided or two-sided?) MAYBE? Common derivation (probably not since different triggers)? Common systematics tasks?

12. Code/Infrastructure • xAOD-based analysis: TokyoTech, UCSC need to catch up • Derivations followed through upon by Milano (status?) • Higher-level statistics and • plotting utility (Ryan…) • Past quantities that have required • study (do we need to look into • these?) • MET • Isolation definition • ???

13. Event Selection: Preliminary Studies • In past, formal optimization was last step, considering only M_eff (or HT) , MET • Individual, preliminary studies used to establish • Photon PT cut; see e.g. https://indico.cern.ch/event/165989/contribution/0/material/slides/0.pdf • Δφ-MET : make use of or not; cut value. Should we also cut on (Δφ-MET - )? • Δφjet-MET : cut value. Should we also cut on (Δφjet-MET - )? • For 8 TeV, used Meff vs. MET visualization plane (see below) • Will need signal grid points for this already!

14. Optimization: 8 TeV Approach • Last step done by inspection of Meff (or HT) vs MET plane • Can be confounded by statistics; also look at background and signal stats over same plane • See 8 TeV backup note WP2 Optimization NO YES

15. Optimization: The Conundrum • How to estimate backgrounds when final background estimates not available? • For 8 TeV analysis optimization, backgrounds estimated by • QCD background estimated by scaling 1 tight + 1 non-isolated pseudophoton sample to 2 tight pseudophoton sample with no Meff (HT) cut for 0 < 60 < MET (DATA) • EW background estimated by scaling e sample by uniform 2% e scale factor (DATA) • W, Z from MC • SUSY group will accept leaving final data-driven step and quick reoptimization before unblinding. Or, pre-optimize as a function of one to-be-determined background value

16. What SRs to Create? • For 8 TeV Analysis • Strong production: High Meff; backgrounds near 0 • EW production: Intermediate HT; backgrounds 1-2 events • Low mass bino, high mass bino for both • SP1, SP2, WP1, WP2 • Also: Model-independent SR (MIS), no Meff (HT) cut. Based on choosing MET cut at which EW and QCD backgrounds about the same (~1 event each)

17. Model-Independent SR (?) 8 TeV analysis: at MET=250, Meff = 0 backgrounds about same EW QCD Question: Should we rethink? What do we really want to do to minimize chance that we miss a signal? Hmmm…. How do we think about this?

18. What Physics Could Hide Signal with Dominant BF into Photons and DM? Degenerate SUSY scenarios? No – energy has to go somewhere. We would see it in photons and/or MET. Photons will not be soft because decaying state will either be high-mass or boosted. Low photonic BF? Would need to accelerate single-photon analyses. Not really practical. Long-lived scenarios? Need to re-create non-pointing photon reconstruction. Probably no competition from CMS here anyway. Perhaps most likely scenario is lower-than-expected cross section from non-SUSY process. Probably best addressed by what was done before, or perhaps just use no Meff or Ht cut and use lower MET cut of the other, model-dependent SRs. Could perhaps also maintain low photon ET cut but that could be a “can of worms”.

19. Wrap UP • I haven’t mentioned limit setting within HistFitter • Immediate motivation is to get to unblind before or simultaneous with CMS • I’m not assuming we’ll necessary be setting limits! • Our work is cut out for us. Thoughts? • We should start writing the skeleton of the backup note. If anyone is itching to do this, by all means. Otherwise, I’m very happy to do that.