TEV PA Meeting July 2009

1. Preliminary Fermi-LAT Limits on High Energy Gamma Lines from WIMP Annihilation Yvonne Edmonds representing the Fermi-LAT Collaboration KIPAC-SLAC, Stanford University TEV PA Meeting July 2009

2. Overview • WIMP Line Intro • The Dataset • Statistical Methods • Preliminary Results • Conclusion

3. time γ γ c c ? ? c c γ Z “The Smoking Gun”: Determining the WIMP Mass from g-Lines • If there is a stable weak scale WIMP it will have a relic abundance similar to dark matter. • For annihilation into gg all photons have energy = WIMP mass. The spectrum is a δor line at the WIMP mass. • For WIMP masses > MZ /2 (= 45.6 GeV) , there is also a line from annihilation into gZ • Lines produced from decay in some WIMP models • Lines are the “smoking gun” for WIMP DM • They give you the WIMP mass! • Unique astrophysical spectrum • Independent of non-local (in energy) background spectrum • Branching fractions for gg, Bf,are typically in the range [10-1,10-4] depending on theory • Limits on line branching fractions can importantly constrain particle physics theory • For lines optimal energy resolution and calibration are important ~3x10-26 cm3s-1 for WIMP hypothesis

4. M. Gustafsson et al. [astro-ph/0703512v1] Inert Higgs A. Ibarra & D. Tran [astro-ph/0709.4593v1] gg line gZ line Flux from recent WIMP Line Theory and Corrections to Continuum Gravitino Decay Radiative Corrections T. Bringmann et al. [hep-ph/0710.3169v2]

5. Determining the shape of a line seen by Fermi-LAT • Used GLEAM Geant4 based detector simulator to simulate delta functions in energy • 20, 50, 100, 150, 200, 250, 300 GeV • Events were generated uniformly over LAT face • Few thousand events at each line energy • Unbinned ML fit to Double Gaussian • Left Plot: Energy Resolution • Right Plot: Fit and Interpolated Line Shapes • Black = IRF from fit to Gleam Simulation (20, 50, 100,150, 200, 250, 300 GeV) • Red = IRF from interpolation for line energies that were not simulated • IRFs are normalized PRELIMINARY

6. 11 Month Dataset • August 8th 2008 + ~11months • All-sky survey mode • Sky Regions: • All Sky minus Galactic Plane |B|<10deg • All Sky minus Galactic Plane Plus Galactic Center (<30deg) • Energy : [20,300] GeV • Diffuse Class Cuts • Zenith Angle cut < 105 ° • PSF at 20 GeV is ~0.1° • Removed point sources using the 9 month Source Catalogue : >1000 sources (0.2deg cut) PRELIMINARY PRELIMINARY

7. 95% CLUL Fitting • Instrument resolution ~10% at 100 GeV • Used bins of size ∆E/E = 20% • Background fitting • B(E) = e-αE, background likelihood function • Unbinned Maximum Likelihood Fit to sb region • Side bands of size ∆E/E= 20% • Signal + background fitting • PDF = NbB(E) + NsS(E) • Fixed background counts, Nb, and pdf, B(E) • S(E) = signal pdf, fixed at the center of bin • Unbinned ML Fit to sb+center region to find Ns • Signal constrained to be nonnegative • 95% CLUL calculated from the error on Ns • Tests of the statistical properties of these methods are being performed. PRELIMINARY sb sb Example Fits

8. Preliminary Eleven Month 95%CLUL for Lines (All Sky minus |B|<10) PRELIMINARY Note: No trial factor included Consistent with 3 month results. For a decaying DM particle

9. Preliminary Eleven Month 95%CLUL for Lines (All Sky minus |B|<10 + Galactic Center) PRELIMINARY Note: No trial factor included

10. Summary • Preliminary eleven month 95%CLUL flux limits on photon lines. • Results are consistent with the expected improved sensitivity relative to the 3 month preliminary results presented at APS and UNESCO conferences. • What’s Next: The 1 year paper. • 1 year of data • Additional statistical methods • Update to most recent set of LAT MC simulations and Instrument Response Functions

11. PRELIMINARY Preliminary Three Month 95%CLUL to Lines (All Sky minus |B|<10) Note: No trial factor included For a decaying DM particle

12. l Line of sight y GC R Y x Calculating the Flux from WIMPs Note: For a decaying DM particle