Update from the Photons + MET Group

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

2. 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. 305 nb-1 Analysis: not approved! Single- 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). Two-

4. 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. Some Developments Since Late July

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

7. 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) < 3 GeV (> 5 GeV used as reversed cut • Underlying event correction was on average about 500 MeV

8. Direct Photon Note Purity Method

9. 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 pT > 20 GeV

10. 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<3 GeV and Etcone40>5GeV • NA: 20226 NB: 5023 MA: 460 MB: 213 • Purity – 0.64  Compare to 0.72 • GMSB note isolation cut • Etcone20/et <0.1 and Etcone20/et>0.125 • NA: 12355 NB: 9081 MA: 201 MB: 405 • Purity – 0.46

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

12. 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. 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. 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