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Update on Diphoton and MET Analysis Techniques for 7 TeV and 8 TeV Data

This update discusses the methodologies and optimization strategies employed in the analysis of diphoton and missing transverse energy (MET) signals, specifically focusing on the transitions from 7 TeV to 8 TeV data. It highlights significant adjustments made to observation parameters, including the adaptation of signal regions for strong and electroweak production, while integrating model-independent selection criteria. Attention is given to the estimation of backgrounds from QCD and electroweak processes, aiming to refine the precision of signal measurements.

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Update on Diphoton and MET Analysis Techniques for 7 TeV and 8 TeV Data

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  1. Diphoton + MET Analysis Update Bruce Schumm UC Santa Cruz / SCIPP 24 January 2014 Editorial Board Meeting

  2. Gauge Mediation Grids for 7 TeV Analysis squark/bino grid gluino/bino grid For 2012 (8 TeV) Data: Replace “constrained” SPS8 grid with wino/bino grid Bino = 10 Wino = degenerate triplet 1 and 20 Production through 1 20 and 1+ 1- “SPS8” Trajectory

  3. 2011 Signal Regions ETmiss = LocHadTopo HT = Scalar sum of all transverse energy (no ETmiss)  = minimum angle between photon and MET Strong production; high-mass bino Strong production; low-mass bino Electroweak production • For 2012: Include additional observables, for certain signal regions: • MEFF (or “HT-prime”) = HT + ETmiss • j = minimum angle between jet and ETmiss • Also: ETmiss is now EGamma10NoTauLoosePhotonRef

  4. 2012 Optimization Strategy • Strong Production (SP1, SP2) • Largely the same as for 2011 analysis • Explore MEFF, j, removal of no-pixel hit requirement for conversion tracks • Tweak cuts for higher mass scales • MEFF somewhat preferable; j provides no apparent advantage • As for 2011, optimal point is largely background-free • Optimize for (mgluino,mbino) = (1300,1050) and (1300,150) • Electroweak Production (WP1, WP2) • No real preference for MEFF, but highly correlated with ETmiss so use HT. • As for strong production, two SRs (low-mass, high-mass bino) •  helps for high-mass bino SR; j helps for low-mass bino SR • Optimal point will have few-event background • Optimize for (mwino,mbino) = (600,500) and (600,100) NEW: Model-Independent Selection (MIS) • Cut at MET for which total background approach the ~1-event level

  5. for strong-production optimization Used wino_bino_600_500, wino_bino_500_100 for weak production > Used background distributions alone for model-independent selection

  6. Re-Examination of No Pixel-Hit Requirement Figure of merit for 1300_150 Point; Removing events for which converted tracks have pixel hits Figure of merit for 1300_150 Point  Remove no-pixel-hit requirement

  7. 1300_1050 (SP1) Optimization Figure of Merit Number of signal events (20 fb-1) Chosen point • Avoid pitfalls: • Rapidly falling signal • Fluctuating backgrounds (above “dips” in FOM) SP1 Optimum: (MET,MEFF) > (250,1500)

  8. Explore (,jet)MET Cuts for SP1 Selection ,MET > 0.5 jet,MET > 0.5 SP1 • Choose (MET,MEFF) = (250,1500) with ,MET > 0.5 • Statistics not so good, but see • Improvement with ,MET cut • Degradation with jet,MET cut

  9. Model-Independent Selection Apply cut jet,MET > 0.5 EW background QCD background No cut on HT or MEFF; just choose point on horizontal (MET) axis for which the backgrounds approach the ~1 event level  MET > 250 GeV

  10. Signal Selection Results

  11. Status of Background Estimation • QCD Backgrounds • EW Backgrounds from e Fakes • Irreducible Backgrounds • Irreducible Backgrounds (for now SP1, SP2 only): • From W, (Z) events • Estimate from MC samples, scaled to 20 fb-1 • Very small for SP1, SP2 (before K factors that are < 3) • For both, before K factors: 0.03  0.01 (stat)

  12. QCD Backgrounds Estimates derived from scaling observed low-MET signal rates to high-MET using control samples Integral above cut provides background estimate Scale to number of signal events

  13. QCD Backgrounds Continued • For each SR, accumulate 8 control samples • In principle, eight independent estimates; establishes systematic range Define Pseudo-photon = loose, plus fail two shower-shape requirements (“Fracs1” and “Weta1”). Each control sample contains at least one pseudophoton. In addition, it must (QCDtg) or must not (QCDg) contain a tight isolated photon. For each of these two choices, we can further have • A cut of either 50 or 75 GeV on the photons (tight and pseudo) • Pseudophoton may be isolated or not • 8 combinations • 5 signal selections • 40 QCD background estimates “Undefined”  no control-sample events OR no signal sample events below MET = 60 GeV If no control-sample events above MET cut  set 90% UCL NOTE: In 2011 only one control sample (QCDg 50 non-isolated I recall)

  14. Propose QCDtg 50 GeV no-isolation for “nominal” estimate SP1 WP1 SP2: Undefined (no signal at any MET!) WP2 Does not exhibit consistency!! MIS

  15. Notes on QCD Background Estimates • SP2 backgrounds undefined since no signal at any MET. However, if you take this as < 2.3 low-MET signal events at 90% CL, control-sample extrapolations yield < 0.5 events at 90% CL • 2011 strong-production estimates were also undefined  developed extrapolation technique (underway now) • Strong-production estimates suggest very small backgrounds, systematics under control • WP1 and MIS estimates larger, but consistent from sample to sample • WP2 estimates inconsistent between QCDg and QCDtg samples. Will require further thought (Osamu Jinnouchi) • Unblind SP1, SP2 first (and perhaps also MIS for the EW grid?) BUT WAIT…

  16. Late-Breaking News: SP2 Extrapolation • Use QCDtg with Et cut of 50 GeV, and do not require “g” to be isolated • Best guess as to most representative control sample • Will try others (with higher statistics) to check Expected QCD background (linear fit): NbackQCD = -0.25 +- 0.49 (or less than 0.55 events at 90%CL)

  17. e EW Backgrounds • Start with determination of the e fake rate • In bins of  • Separately for converted, unconverted photons e final state ee final state Fake rate is (roughly) the background-subtracted ratio of these two yields

  18. Fake Rate Results

  19. SP1, SP2 Backgrounds at First Blush EW background from e   fakes determined by scaling observed e events by measured e fake rate. SP1: no e events observed  < 0.07 events expected background SP2: 1 e event observed  0.03 +- 0.03 expected backgrounds • Once QCD extrapolation studies are done, SP1, SP2 backgrounds should be in good shape. • Document and request unblinding next week? • Might we also want to finish MIS background studies? (No extrapolations needed for QCD

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