1. Update from the Photons + MET Group Bruce Schumm UC Santa Cruz / SCIPP 26 August 2010 SUSY/MET Meeting

2. 26 August 20102 This presentation is largely informal and unofficial Vacation/conferences: no official strategizing session yet Some opinions/thoughts will be presented, but are only from a subset of the group Intended to prompt discussion, or at least show the issues we’re considering as we re-group

3. 26 August 20103 305 nb -1 Analysis: not approved! Single-  Two-  Statistics dictated that we concentrate on a single-photon analysis, even though we expect to require two photons in the photons+MET analysis to reject SM backgrounds (e.g. setting GMSB limits).

4. 26 August 20104 Why not approved? Main (QCD) background scaling not understood –K factors and ad-hoc scaling factors –Mis-id rates –Dijet vs.  +jet contributions –MET spectrum too hard? Could not benchmark against direct photon analysis at low MET Non-standard analysis steps (isolation)? No independent constraints on mis-ID rates (jet  )

5. 26 August 20105 Some Developments Since Late July

6. Photon Purity for GMSB Photon Sample  Benchmark analysis against Direct Photon study Daniel Damiani

7. 26 August 20107 Direct Photon Note Purity Method Method for photon purity calculation was taken from ATLAS-CONF-2010-077 A two dimensional side-band background subtraction was used to measure the purity Two sets of cuts were reversed: –Tight Photon Strip Isem cuts DeltaE Fracm Wetalc DEmaxs1 –Isolation Etcone40 – (underlying event correction) 5 GeV used as reversed cut Underlying event correction was on average about 500 MeV

8. 26 August 20108 Direct Photon Note Purity Method

9. 26 August 20109 Direct Photon Note Purity Method Formula used to calculate the purity in direct photon note: Data set used: 15.8nb -1 Extracted purity 0.72±0.07 for tight photons with p T > 20 GeV

10. 26 August 201010 Purity Measurement – GMSB Sample Used 305 nb -1 of 7 TeV data Same shower shape cuts were reversed Direct photon note-like isolation cut –Etcone40 5GeV –N A : 20226 N B : 5023 M A : 460 M B : 213 –Purity – 0.64  Compare to 0.72 GMSB note isolation cut –Etcone20/et 0.125 –N A : 12355 N B : 9081 M A : 201 M B : 405 –Purity – 0.46

11. Breakdown of Background Sources  Data-driven background estimation strategy may be source-dependent Andrea Bangert

12. 26 August 201012 Where from Here? One thought: 10 pb -1 prototype analysis (i.e. 2010 data set) 10 pb -1 not enough to improve, e.g. on Tevatron GMSB (SPS8) limits Should be enough to –Develop analysis (background estimation) techniques –Prepare for publishable limit –[Generate PhD theses]

13. 26 August 201013 10 pb -1 “proto”-Analysis Scaling up, would have 50-100 diphoton events Perform analysis optimized for scaled- back limit (MET, HT cuts); fast-MC-based re-optimization underway Would likely circumvent issues encountered in late July (second photon likely to greatly suppress QCD backgrounds)

14. 26 August 201014 Summary The strong and weak production mechanisms contribute as we had come to suspect There is a third intermediary type of events, but its cross section is very small Strong production component is already pretty small at Λ=90 for 7 TeV and drops off quite quickly from there No real revelations here but at least it conforms what we had suspected was going on