1. From GMSB to Photons plus Missing E t : Some Thoughts on Model Independence SUSY/E t Miss “Kickoff” Meeting February 5, 2010 Bruce Schumm, UCSC/SCIPP

2. Concern (expressed by audience member during a prior presentation by our group): The group has tuned its analysis on (essentially) one GMSB trajectory. What if SUSY chooses some other way to manifest photon + E t Miss signature(s)? In other words: how model independent is our approach; i.e., are we the GMSB group or the photons plus missing Et signature group? As pointed out, from an experimental standpoint, the latter is more justifiable.

3. So, we agree model independence is laudable. Problem: you can’t tune an analysis without a model (or at least, an ad-hoc signature) to preserve while exploring ways to reject backgrounds. Observation: Two photons is quite a robust signature. Trouble would probably arise from single-photon signatures. So: Is there any photon + MET SUSY signature that would suffer from requiring two photons?  Are there single-photon plus MET SUSY signatures?

4. Yes (perhaps)… GMSB (non-minimal) Certain parts of MSSM can have significant radiative decays Under what conditions? Consult Gunion & Haber, hep-ph/9806330 (general picture) Ambrosanio and Mele, Phys. Rev D 55, 1399 (1997) (Radiative scenarios in MSSM)

5. Photons in “Standard” GMSB For us, GMSB phenomenology is NLSP   G, where “G” is gravitino: In much of (minimal) GMSB parameter space the NLSP is a  0 that is essentially the B-ino, decaying via  0  ( ,Z) G with the Z channel suppressed by tan 2  W, and by kinematics (depending on  0 mass). Thus, NLSP decay is dominated by  G, and we get two photons in a majority of events.

6. Photons in Generic GMSB If the NLSP (  0 ) is mostly Higgs-ino or W-ino (or a mixture of the two), the  G decay will be suppressed. In this case, single-photon searches may be more optimal, and there would be fewer  +MET events overall  We might miss this signature with our current analysis

7. Single Photon Signatures in MSSM Consider (fairly common) region of parameter space for which  1 0 is LSP. Common end-of-chain decay is  2 0   1 0 + X, with X dominated by tree-level two-fermion (f f ) decay. Radiative decays  2 0   1 0  occur at loop level, and are g 2 -suppressed. However, there are two regimes (“dynamical” and “kinematic”) for which  2 0   1 0 f f can be even more heavily suppressed than  2 0  1 0  …

8. Dynamical Suppression Tree level decays require  1 0,  2 0 to have simultaneous Higgs-ino or simultaneous gauge-ino components. There is no similar constraint on loop-level decays. Kinematic Suppression Mass degeneracy M(  2 0 )  M(  1 0 ) closes off phase- space more quickly for three-body (tree-level) decay relative to two-body (radiative decay) Together, these can suppress f f decay relative radiative decay, leading to appreciable photonic decay rates.  Again, single-photon signatures may provide best signal.

9. Proposal (Schumm, Kuhl, Hayward) Begin with “standard” SPS-8 GMSB, and alter  1 0 branching fraction by hand to point at which single- photon signatures might provide best approach. Explore performance of two-photon vs. single-photon analyses as a function of photon BF. May well discover that signal becomes undetectable for photonic BFs that favor single-photon analysis. Or not – would be instructive either way. Thoughts?