1 TEV PA MeetingJuly 2009

Preliminary Fermi-LAT Limits on High Energy Gamma Lines from WIMP Annihilation

Yvonne Edmonds representing the Fermi-LAT Collaboration

KIPAC-SLAC, Stanford University

2

Overview

• WIMP Line Intro

• The Dataset

• Statistical Methods

• Preliminary Results

• Conclusion

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“The Smoking Gun”: Determining the WIMP Mass from -Lines

• If there is a stable weak scale WIMP it will have a relic abundance similar to dark matter.

• For annihilation into all photons have energy = WIMP mass. The spectrum is a δ or line at the WIMP mass.

• For WIMP masses > MZ /2 (= 45.6 GeV) , there is also a line from annihilation into Z

• 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 , 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

γ

γ

?

time

γ

Z

?

annihilvBv

~3x10-26 cm3s-1 for WIMP hypothesis

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A. Ibarra & D. Tran [astro-ph/0709.4593v1]

Flux from recent WIMP Line Theory and Corrections to Continuum

Gravitino Decay

Z line line

Inert Higgs

M. Gustafsson et al. [astro-ph/0703512v1]

Radiative Corrections

T. Bringmann et al. [hep-ph/0710.3169v2]

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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

PRELIMINARY

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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

PRELIMINARY

PRELIMINARY

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PRELIMINARY

PRELIMINARY

• 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.

95% CLUL Fitting

Example Fits

sb sb

8),,( lbdd

Mv

ROIll

0

2

24

For a decaying DM particle

mmv 2

21,

Note: No trial factor included

Preliminary Eleven Month 95%CLUL for Lines (All

Sky minus |B|<10)

PRELIMINARY

PRELIMINARY

Consistent with 3 month results.

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Preliminary Eleven Month 95%CLUL for Lines (All

Sky minus |B|<10 + Galactic Center)

PRELIMINARY

PRELIMINARY

Note: No trial factor included

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• 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

Summary

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Preliminary Three Month 95%CLUL to Lines (All Sky minus |B|<10)

),,( lbdd

Mv

ROIll

0

2

24

For a decaying DM particle

mmv 2

21,

Note: No trial factor included

PRELIMINARY

PRELIMINARY

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GC

Line of sight

R

l

xY

Calculating the Flux from WIMPs

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GeVcmkpcR

ar

GeVcm

ar

ar

GeVcm

ar

ar

GeVcm

LBRllRlr

dldlrBdE

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mE

coreisoMNFW

R

coreiso

coreiso

MM

Moore

NFWNFW

NFW

f l

ff

42820

3008

1

15

1

530

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42

2

24

1

3

2

3

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22

,,

.,.

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coscoscos,cos),(

,),(),(

..

,

Note: For a decaying DM particlemm

v

1

2 2

2