Issues and Run-II Musings About the  +MET Analysis

1. Issues and Run-II Musings About the +MET Analysis Osamu Jinnouchi (Tokyo Tech), Ryan Reece (SCIPP), Sheena Schier (SCIPP), Bruce Schumm (SCIPP) Prepared for the Inclusive Strong Production Sept 2014 Oxford SUSY Workshop Live Page

2. NOTE!!! This set of slides covers all the areas of the review within this single set. However, the sections are clearly separate out, and the background material provided by the other sections will likely help anyone reviewing them to understand what they are. Apologies…

3. Conference Note public in early January 2014: Search for Supersymmetry in Diphoton Events with Large Missing Transverse Momentum in 8 TeV pp Collision Data with the ATLAS Detector ATLAS-CONF-2014-001 Final result in preparation

4. Diphoton+MET Personnel (beginning of R2) Osamu Jinnouchi, Tokyo Tech Faculty Ryan Reece, UCSC/SCIPP Post-doc Sheena Schier, UCSC/SCIPP Ph.D. Graduate Student Bruce Schumm Faculty XXX, Tokyo Tech Unnamed Masters Student Possible additional contributors (encouragement welcome!) Khliesh Mistry, U. Pennsylvania Ph.D. Graduate Student Brig Williams, U. Pennsylvania Faculty

5. Summary of SRs SP (WP): Strong (Weak) production 1 (2): High- (low-) mass bino production MIS: Selection driven purely by expected background studies

6. Summary of Backgrounds Data Driven Data Driven Data-scaled MC Pure MC

7. Opening Note: Diphoton+MET Triggers • All Diphoton+MET SRs require two tight photons with ET > 75 GeV • However, QCD control region makes use of a subset of [loose-tight] (as well as tight) photons with ET > 50 GeV • The QCD control samples are statistically limited • In RUNI, we used 2g40_loose trigger • RUN2 proposal is medium photons of 35 and 25 GeV • We have not had a chance to study the effect of the potential reduction in control sample sizes due to going from loose to medium.

8. Section I: Data Driven Backgrounds Background A: QCD • Define various control samples • “t”  require 1 tight, iso photon • “g” = pseudophoton (reverse two PID bits) • “g” can be isolated or not • QCDg • QCDg+iso • QCDtg • QCDtg+iso • QCDtg+iso reproduces  MET dist well but limited statistics • QCDtg reproduces QCDtg+iso well at high MET, fair stats • QCDg provides high statistics but has higher tails

9. Section I: Data Driven Backgrounds Background A: QCD • Background estimated by applying all cuts save MET and then scaling control sample (QCDtg) to  distribution • Could work on quality of control sample agreement with  distribution (study effect of relaxing isolation requirement, etc.) • Could revisit contribution from true  background which does not have jet   fake and might have different MET distribution (but was seen to be small in prior versions of analysis) • Could think about new approach… ?

10. Section I: Data Driven Backgrounds Background B: Electroweak Me (converted photon) Me (unconverted photon) • Estimated via dedicated e control sample scaled by measured e fake rate (fairly standard) • Studies show 25% of W/Z/t- backgrounds do not have e fake, but some of this expected to be incorporate in “QCD” background estimate •  Adopt +-25% systematic uncertainty. Want to reduce with further study.

11. Section I: Data Driven Backgrounds Background C: W Irreducible Background Concern: very large K factor arises from elimination of a cancellation when gluon radiation included Associated with higher values of W system recoil (pT,l) Our selection places all our W background at high values of pT,l Our MC model (Alpgen) not a full NLO model  Constrain W contribution from data NLO LO

12. Section I: Data Driven Backgrounds Background C: W Irreducible Background Constrain W K-factor for pT,l > 100 Constrain K-factor with dedicated l control sample W contribution (white) includes x3 “enhancement factor” relative to Alpgen Actual analysis makes use of simultaneous fit to control and signal region, but in limit of 0 signal, W floats up to about x3 in fit.

13. Section I: Data Driven Backgrounds Background C: W Irreducible Background However: *) Subsequent MC-based studies by Ben Kaplan showed good agreement between Alpgen and a full NLO calculation https://indico.cern.ch/event/319991/contribution/3/material/slides/0.pdf *) A direct measurement (data!) of W production in the SM Working Group, although in a slightly less restricted kinematic space (looser selection cuts) support the x3 enhancement factor at some level  Needs to be resolved Ben Kaplan  Can we use VBFNLO as a generator for our W background samples?

14. Section II: Direct Use of MC Use A: Direct Estimate of Z Background • Makes use of Sherpa for kinematic distributions • Sherpa cross section corrected by ratio of Sherpa cross section to MadGraph NLO cross section calculation over same kinematic region • Result used directly to estimate Z backgrounds to both signal and l control regions • Scale uncertainty of 50% assumed – can this be reduced with further study? • Consider data-driven Z study • Does SM group have corresponding analysis?

15. Section II: Direct Use of MC Use B: Estimating Backgrounds to l Con-trol Sample • W, Z Z and ttbar- backgrounds to the l control sample are estimated directly from the MC • All appropriate K-factors are used • In the control region pT,l they are small

16. Section II: Direct Use of MC Potential Use C: Possible tt Background At 13/14 TeV, might the tt start to contribute at an appreciable level?  Need to explore this, perhaps even with new (?) dedicated MC sample.

17. Section III: Signal Studies – Pointing vs. Non-Pointing Photons • For prompt photon analyses (ours!), there is a tension between the bino decay length for low bino mass and direct decays of strongly produced states (gluinos, squarks) to gravitinos for high bino masses. • Finessed by fine tuning of the coupling between SM and gravitational sectors – we have always felt this to be a bit unnatural • Have talked for some time about making the bino lifetime a third dimension in the parameters space (e.g. a parameter space in the three dimensions of gluino mass, bino mass and bino lifetime) • This would involve generating 3D grids and combining the prompt diphoton+MET and non-prompt-photon analyses • Note that CMS already makes use of 3D parameter spaces – gluino mass, squark mass, bino mass – but the idea of having bino lifetime be a parameters in this manner would be both natural and unique to ATLAS.

18. Section IV: Early Data Strategy Trigger Perspectives • For Run 1 (8 TeV) we used 2g40_loose (two >40 GeV loose EM objects) • Our offline SR selections made use of tight photons down to 75 GeV • Our offline CR selections made use of tight and loose photons down to 50 GeV (lower ET needed to procure statistics • For our future analysis, we believe that the appropriate trigger will be • 2gXX_loose • where XX is as low as possible. It would be good to know ASAP what XX might be expected to be.

19. Section IV: Early Data Strategy Follow-up on Run I Excess (?) • Our WP2 selection identified 5 events over a background of 2.4  0.6 • 1.6 sigma excess • May not warrant special attention but in the spirit of due diligence we point this out.