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Status Update for: Search for Heavy, Long-Lived Neutralinos in the g +MET+Jet+Track Final State

Texas A&M Group: Paul Geffert , Max Goncharov*, Slava Krutelyov**, Eunsin Lee, David Toback and Peter Wagner*** * Now at MIT ** Now at UCSB *** Now at Penn. Status Update for: Search for Heavy, Long-Lived Neutralinos in the g +MET+Jet+Track Final State. Previous Analysis:.

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Status Update for: Search for Heavy, Long-Lived Neutralinos in the g +MET+Jet+Track Final State

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  1. Texas A&M Group: Paul Geffert, Max Goncharov*, Slava Krutelyov**, Eunsin Lee, David Toback and Peter Wagner*** * Now at MIT ** Now at UCSB *** Now at Penn Status Update for:Search for Heavy, Long-Lived Neutralinos in the g+MET+Jet+Track Final State Paul Geffert -Texas A&M University

  2. Previous Analysis: • Delayed Photon Analysis in the g+MET+Jet final state published in PRL • PRL 99, 121801 (2007) • Published more details in a full PRD • PRD 78, 032015 (2008) Paul Geffert -Texas A&M University

  3. Outline • Motivation and Theory • Brief Summary of Previous Analysis • Next Generation Analysis and Strategy • Optimization • Results • Conclusions Paul Geffert -Texas A&M University

  4. Motivation and Theory • GMSB models predict heavy neutralinos that decay to photons • The lightest neutralino can be the NLSP and decay into a gravitino and a photon • Cosmological constraints favor neutralino decay times ~ns • At the Tevatron neutralinos are pair produced from Paul Geffert -Texas A&M University

  5. Brief Summary of the Analysis Signature Leave the detector Can be identified Can be identified • analysis is sensitive to ns lifetimes while analysis is sensitive to prompt neutralino decays Full GMSB strategy: Long and Short lifetime neutralinos • Toback and Wagner, PRD 70, 114032 (2004) Paul Geffert -Texas A&M University

  6. Summary of Original Analysis • Final Cuts: g Et>30GeV, Jet Et>35GeV, Dphi(Jet,MET) >1rad, MET>40GeV • Backgrounds: SM 0.71±0.60, Cosmics 0.46±0.26, Beam Halo 0.07±0.05  Total 1.3±0.7 • 2 events in signal region Paul Geffert -Texas A&M University

  7. Analysis Strategy • Create g+MET preselection sample • Use background distributions to make predictions for different cuts • Optimize for GMSB with ns lifetimes • Use new techniques to improve original analysis • Use lessons from last time to improve the analysis Paul Geffert -Texas A&M University

  8. Analysis Changes • Change to STNtuple  Different tracking • Add a High Pt track • Add new Beam Halo and Cosmic rejection Paul Geffert -Texas A&M University

  9. Tracking Changes • Original analysis used a custom Ntuple; we use Stntuple • Track T0’s not quite as well corrected • Slightly larger RMS for right and wrong vertex timing • Right vertex: 0.64 ns  0.74 ns • Wrong vertex: 2.05 ns  2.11 ns • Gaussian out to many s ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 9

  10. Reproducing Original Analysis • Applied optimal cuts from original analysis to our new dataset • SM 0.711.45, Cosmics 0.460.60, Beam Halo 0.070.05 • More SM due to larger track T0 RMS • Acceptance 6.1%  5.1% or 5.74.7 events • Fixed a bug in the original ntuples that messed up vertexing • Cross section limit: 128 fb 187 fb ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 10

  11. Next Generation Improvement New optimization variable: Isolated, high Pt track • Uncommon in SM collisions • Can also reject non-collision backgrounds • From t’s in the decay chain • Track could be from e’s or m’s if model is wrong so some model independence • Use standard definition of isolation: SPt of good tracks in a 0.4 cone Paul Geffert -Texas A&M University

  12. Next Generation Improvements • Ideas for Cosmic Ray and Beam Halo rejection from CDFNote 7960 (don’t use exact suggestions) • Cosmics: Photon must have CES Energy>10 GeV (not biased against delayed photons) • Beam Halo: Less than 2 Plug Hadronic and 8 Central EM tower hits in same wedge as Photon (standard rejection) ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 12

  13. Preselection Requirements New CDFNote 7960 Paul Geffert -Texas A&M University

  14. Background Sources Two major background types: CDFNote 7960 • Standard Model Collision Events • Photon is matched to correct vertex (“right vertex”) or not (“wrong vertex”) • Corrected times centered around 0ns • Non-Collision Events • Beam Halo • Corrected times mostly less than 0ns • Cosmic Rays • Occur uniformly in time Note: We use the standard definition for vertex corrected photon times. Paul Geffert -Texas A&M University

  15. Background Estimation • Fit the data to background timing templates in different timing control regions • Extrapolate to the signal region, where we expect delayed photons • Described in CDFNote 7960 ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 15

  16. Timing Distribution for “Right” and “Wrong” Vertex Selection • Plots are from Stntuple • Top- Electron track matches vertex (“Right Vertex”) • Bottom- Electron anti-matched to vertex (“Wrong Vertex”) • With low wrong vertex backgrounds, potential bias problems are small Paul Geffert -Texas A&M University

  17. Timing for Beam Halo and Cosmics Cosmics Events/ns Beam Halo Events/ns The corrected time distributions for beam halo (left) and cosmic ray (right) backgrounds from the Stntuple Paul Geffert -Texas A&M University

  18. Next Generation Improvements • Cosmic Ray and Beam Halo rates drop significantly with minimal loss of efficiency Presample predictions after BH/CR rejection Presample predictions before cuts ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 18

  19. Optimization Variables Everything varied simultaneously to find true minimum A full list of optimization variables: • Jet Et • Vertex SPt • Dphi between the Jet and Missing Et • Lower limit on signal timing region • Upper limit on signal timing region • Isolated Track Pt Variables that did not help: • Photon Et • Missing Et • Ht • Missing Et Significance New Variables ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 19

  20. Optimized Cuts Use GMSB point with neutralino (mass, lifetime) = (100 GeV, 5 ns) Assume a 10% systematic error on acceptance (same as PRD) ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 20

  21. Jet Et N-1 plots: All other variables held at their optimal values Vertical lines show optimal cut value • The expected 95% C.L. cross section limit vs. cut • The bins at or below 0 represent the case of no Jet • Helps reject non-collision events • There is a cosmics event with Jet Et > 800 GeV • Adding a jet clearly helps ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 21

  22. DPhi(Jet,Met) • Reject events with poorly measured Jets that create Met • Mostly gets rid of QCD ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 22

  23. Missing Et • Signal has real Met due to neutrinos and gravitinos • Reject SM events with mismeasured timing but no real Met • There is a cosmics event missing from left plot with Met > 800 GeV ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 23

  24. Isolated Track Pt The bin below 0 represents the case of no Track • Very good at non-collision event rejection • Could be from taus in the signal • Adding an isolated track clearly helps ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 24

  25. Lower Timing Cut Minimal gain by changing the value • Left- The timing distribution for the signal and all backgrounds Paul Geffert -Texas A&M University

  26. Background Prediction Consistency • The number of events in [-10,-2] ns matches the prediction for [2,10] ns ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 26

  27. New Optimization vs. Old Optimization • Similar final cuts to original analysis • Added Isolated Track with Pt > 5 GeV • Loosened Vertex SPt from 15  5 GeV • Jet Et dropped from 35  20 GeV • Met dropped from 40 GeV  35 GeV • Dphi(Jet,Met) decreased from 10.4 rad • Signal timing region unchanged [2,10] ns • Cross section limit: 187 fb 127 fb • Each limit calculated using new dataset ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 27

  28. Conclusions • Completed preliminary re-optimization of the delayed photon analysis • Adding an isolated track helps by allowing us to loosen other cuts • ~40% improvement after re-optimization • Checking to see if adding a track/no jet and no track/jet samples will help • Slides 20 and 23 indicate this is unlikely • Next step is to add more data ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 28

  29. Backup Slides Paul Geffert -Texas A&M University

  30. Track and Jet Delta R Delta R distribution between the jet and isolated track for optimized cuts The track and jet often the same • Want to determine if we should require: • Only a jet • Only a track • A jet OR a track (exclusive or) • A jet AND a track Data ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 30

  31. Met Significance • Helps reject events with Met due to poor measurements ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 31

  32. Vertex SPt • Helps reject non-collison events ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 32

  33. Ht • There is a cosmics event missing from left plot with Ht > 1600 GeV ?/?/09 SUSY Meeting Paul Geffert -Texas A&M University 33

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