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First Look at Conversions for Non-Pointing Photons

First Look at Conversions for Non-Pointing Photons. US ATLAS Egamma Meeting March 12 2009 Bruce Schumm, UCSC/SCIPP. Motivation Gauge-mediated supersymmetry breaking (GMSB) tends to have a Gravitino (G) LSP, with a decay-chain ending with  0  G + 

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First Look at Conversions for Non-Pointing Photons

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  1. First Look at Conversions for Non-Pointing Photons US ATLAS Egamma Meeting March 12 2009 Bruce Schumm, UCSC/SCIPP

  2. Motivation Gauge-mediated supersymmetry breaking (GMSB) tends to have a Gravitino (G) LSP, with a decay-chain ending with 0  G +  Since gravity is weakly coupled, the neutralino (0) can be metastable, leading to hard photons that don’t point back to the collision point. Studies (Helen Hayward, Mark Terwort) suggest that CAL can be used to detect these and constrain decay length, masses.

  3. Initial goal: include conversions in reconstruction Mauro Donega, UPenn Reconstructed radius of material-induced conversions • Conversion radius resolution may be good enough to provide an independent constraint on GMSB parameters • Pointing accuracy of reconstructed conversion may be quite good

  4. Reminder: Reconstruction Working with 627 GMSB1 events reconstructed with 14.5.0 Reminder: Truth Matching Have worked through “track” truth matching for conversions (thanks to code snippet from Thomas). Truth match only if an electron or positron from a photon conversion (1-track conversions) or one electron and one positron from a photon conversion (2-track conversions). ~ 60% are truth matched

  5. Reconstruction Comparison for Truth-Matched Conversions (compare true photons with EGamma photon reconstructed from conversions) Define scaled momentum difference P as (preco – ptruth)/ptruth Scaled momentum difference for truth-matched conversions

  6. P-difference for 1-track Conversions P-difference for 2-track Conversions Separate 1- and 2-track conversions What could be causing this smearing? Am I truth-matching correctly? Look at the scaled momentum difference for the individual conversion electrons, and also for unassociated pions…

  7. Indivudual Track Comparisons Electron momentum difference  Truth-matching correct?  Electron reconstruction compromised by bremsstrahlung (brem recovery?) Pion momentum difference

  8. Cataloging True Conversions In preparation for studying reconstruction efficiency, separate conversions into those from GMSB photons and those not from GMSB photons. Further discriminate for GMSB-related conversions: “Secondary”: arises from bremsstrahlung of a GMSB-conversion electron “Good”: conversion of a direct GMSB decay photon with pt > 10 and || < 1.5 “Bad”: direct GMSB decay photon that is not “Good”

  9. Categorized Conversion Momentum Distributions NOT GMSB GMSB “GOOD” GMSB SECONDARY GMSB “BAD” Two-track Conversions

  10. Angular distribution of GMSB Conversions GMSB “Good” eta

  11. Radial distribution of GMSB Conversions GMSB “Good”

  12. Latest work (yesterday): Efficiency and accuracy of GMSB Good NOTE: Eff. based on STRICT truth-matching GMSB “Good” efficiency vs. conversion radius

  13. Efficiency vs. angle and pt eta pt

  14. Accuracy of Good GMSB momentum reconstruction 1-track conversions 2-track conversions

  15. Accuracy of Good GMSB conversion radius reconstruction 1-track conversions 2-track conversions Can we make use of 1-track conversions?

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