1. Diphoton+X 2015: Overview of Plans and Goals
Bruce Schumm
SCIPP
On Behalf of the Photon+X Working Group
La Plata, LPNHE Paris, Milano, Tokyo Tech, UCSC
03 June 2015

2. 8 Tev Results Draft includes Diphoton Photon+b Photon+jets Photon+l
Exercise of mushing all four results together in a single paper was taxing but worthwhile
 Can we work more closely together to make the combined paper easier and more natural to write?
June

3. Photon + X Group Organization
New Photon+X Twiki (thanks to Hernan)
Meetings (plan on 90 min) Mondays 16:30 CERN time
Chaired on rotating basis by Photon+X contact people
Leonardo Carminati (Milano)
Bruce Schumm (UCSC)
Hernan Wahlberg (La Plata)
June

4. Photon + X Group Commonality
TASKS POTENTIALLY COMMON TO ALL GROUPS
SM MC samples
xAOD framework issues
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?)
Common systematics tasks?
Common journal submission
June

5. 8 TeV Gluino-bino model limits 8 TeV Wino-bino model limits
Diphoton Analysis
8 TeV Gluino-bino model limits
8 TeV Wino-bino model limits
June

6. Tasks Overview KEY: DONE UNDERWAY UPCOMING Code/Infrastructure
xAOD
Derivations
Higher-level infrastructure (Ryan’s package)
Events variables (MET with photons, etc.)
Event selection
Preliminary studies
Optimization
Backgrounds
QCD
Electroweak
Irreducible
Models
SM samples
Strong & EW signal
Full vs. fast sim
(More on this in a moment)
May

7. Focus Points for Diphoton Analysis
As before, optimize separately for low/high bino mass for both strong (gluino) and EW (wino) production
Assume same a*e (about 12%) and expected #events limits (3 events for strong and 5 events for weak production)
Assume 1.5 fb-1 luminosity at 13 TeV
Mass of focus point is that giving cross section of
3 events = (1.5 fb-1) * (gluino) * (0.12)  gluino = 17 fb
5 events = (1.5 fb-1) * (wino) * (0.12)  wino = 28 fb
 Mgluino = 1500 GeV Mwino = 600 GeV
June

8. Diphoton Analysis Issues
Not planning to use SUSY derivations (using EXOT10)
Next big step to get underway is optimization; for this we await completion of the MC samples
Only need four signal focus points (40,000 events)  Can we get highest priority for these points?
Also need , -jet, W, Z, tt, W and Z samples in order to perform optimization
June

9. Starting to work on backup note
June

10. Thoughts About Diphoton Analysis Timeline
Optimization should take ~2 weeks once MC samples are available (July 1?)
Background estimate techniques in place on roughly the same time scale
Except for QCD background, approaches largely identical to those of the 8 TeV analysis, but almost all rely on controls making use of 13 TeV data
Will develop control samples with limited initial data but will need to run through full data set and assemble estimated when the full sample becomes available.
June

11. 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)
May

12. Gluino-Bino Grid (not quite final version)
May

13. Wino-Bino Grid (also not quite final)
May

14. 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
May

15. 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?
May

16. 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
May

17. 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.
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!
May

18. 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
May

19. 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?
May

20. 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
???
March

21. 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
March

22. 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)
March

23. 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?
March

24. 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”.
March

25. 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.
March