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Update on the Diphoton + MET Analysis

Update on the Diphoton + MET Analysis. Bruce Schumm, channeling Ben Auerbach (Argonne), Osamu Jinnouchi (Tokyo Tech), Susan Fowler (Penn), Brig Williams (Penn), Khilesh Mistry (Penn), Ryan Reese (SCIPP), Sheena Schier (SCIPP) UC Santa Cruz / SCIPP 17 June 2014 SUSY Background Forum Meeting.

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Update on the Diphoton + MET Analysis

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  1. Update on the Diphoton + MET Analysis Bruce Schumm, channeling Ben Auerbach (Argonne), Osamu Jinnouchi (Tokyo Tech), Susan Fowler (Penn), Brig Williams (Penn), Khilesh Mistry (Penn), Ryan Reese (SCIPP), Sheena Schier (SCIPP) UC Santa Cruz / SCIPP 17 June 2014 SUSY Background Forum Meeting

  2. Conference Note public in early January: 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 List of Tasks generated to move from note to paper…

  3. Analysis Strategy (lower reach of Wino-Bino limits) Also: require ET > 75 GeV for each of the two photons • Low-mass winos lead to limited • Photon ET • MET • Overall energy scale • -MET • Efficiency may fall off faster than cross section rises leading to a lower limit on the wino mass scale • Appears to be below 300 GeV (lowest mass simulated) • Lower masses now simulated… will be analyzed soon.

  4. MC Generation/Simulation Tasks • There were several issues to address that required more MC • Low mass wino  Extend grid from 300 GeV down to 100 GeV •  This is high cross-section/low-efficiency regime; required working out filtering mechanism • Low mass bino  Extend explored bino mass reach down from 50 GeV to 10 GeV for all gluino, squark, and wino masses  Requires care to avoid metastable states, direct gravitino decays (our model requires decay through bino) • Nearly degenerate case for EW production (M_bino close to M_wino)  Add points with m of 25 and 10 GeV Again need to watch for pathologies • Now done; awaiting analysis

  5. Analysis Tasks • Increase jet ET cut from 20 to 40 GeV (M_eff reconstruction)  very little change to anything • Evaluate pT dependence of e   fake rate •  play role in determination of EW background •  evaluated with “tag and probe” method •  No significant pTdependence observed • Check grids developed for other signatures •  DISCUSS

  6. Background Studies • Estimate H   background •  Use existing H   MC sample •  Pass through all 5 analysese •  Contributions at 10-2 level or less • Re-evaluate jet-MET uncertainty •  Inclusion of overflow bin made diphoton and control distributions much more similar •  Reduce uncertainty accordingly (small change in overall background uncertainty • Re-examine QCD/EW background overlap uncertainty •  25% of EW backgrounds do not involve an e fake •  MC truth enumeration of processes suggested they might instead be included in QCD background •  ± 25% uncertainty adopted •  Do more explicit study to determine overlap; perhaps reduce 25% uncertainty (Underway; not considered necessary)

  7. Background Studies: New Issue • New developments on W background calculation (Kaplan, Haas) •  Our “enhancement factor” of ~3 is relative to Alpgen •  Kaplan/Haas implement VBFNLO; see that Bozzi et al. NLO is consistent with Alpgen •  Expect no need for enhancement factor Bozzi et al. Kaplan/Haas

  8. Background Studies: New Issue Cont’d • On the other hand, our W background estimate based on e control sample. •  Our “enhancement factor” of ~3 is relative to Alpgen •  Is this incompatible with Kaplan/Haas (phase space..) •  Have we missed some background to the e control sample? •  Can just expand error to include Kaplan/Haas result (but we do simultaneous fit… so need to understand how to do that!) Includes x3 enhancement factor

  9. Signal Systematics • Include photon ID systematics correlations  Done! • Explore differences between ATLFAST and full sim •  Several point in EW have both •  differences at few percent level •  No action taken; new points in full sim but we intend to use either with impunity

  10. Interpretation/Limits • Redo gluino/bino contour (changes very slight, except extension to Mbino < 50 • Set limit in squark/bino plane, including low bino mass • Set limits in wino/bino plane, including lower limits (additional MC needed; hope to submit soon • [Depending on manpower: Set limits in constrained SPS8 model (signal MC already in place)] • Squark/binolimits done except low binomass

  11. Wrap-Up • Most of proposed work towards paper completed • Major issue is loss of Ben Auerbach; are recovering. Cut flow now matched by Osamu; Reese/Schier almost there too. • Osamu working on getting up to speed on fitting/limit-setting. • If expanding systematic error on W background felt to be necessary, then will need to figure out how to do that with simultaneous fitting of W and signal. • Changes so far documented in new backup note <http://cds.cern.ch/record/1700554>

  12. BACKUP

  13. Analysis Strategy Continued 5 fb-1 analysis required ET > 50 GeV and Not good • 1 fb-1 analysis required • ET > 25 GeV • MET > 125 GeV • These will likely place lower limits on the wino mass than those of the 8 TeV analysis (which are still being determined) • Estimate of lower wino limit for 1 fb-1 analysis underway… but can we really include that in a paper? DISCUSS

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