1. LAT performance for DC2 and the “4-panel plot”
Toby Burnett
DC2 workshop 28 June 05 - T. Burnett

2. The proposal, motivated by Steve
Update the LAT performance plots now at
Use all_gamma updated for DC2
Connect with Science Tools versions of the IRF functions (see Jim’s talk)
Question:
Can one reliably use IRF functional representations?
DC2 workshop 28 June 05 - T. Burnett

3. My PSF and Point Source Sensitivity Analysis
There are three memos in LAT docs on the subject:
AN-3455, a proposed PSF functional representation
Propose that we formally adopt it
AN-3456, analysis of all-gamma with GR v4r2, DC1 cuts, including fits to the PSF and Aeff
AN-4369, Implications for point source sensitivity.
Two plots from this memo are in the LAT performance page
Examine the functional form
DC2 workshop 28 June 05 - T. Burnett

4. The PSF function: 2 parameters
Let  be the deviation between actual and measured direction (McDirErr in tuple-speak), and define the scale factor . Then define the scaled difference u = 0.5(/ )2
If both projected distributions are Gaussian, then 2= x2+ y2  is the standard deviation, and the probability distribution for u is exp(-u).
What we observe is not exp(-u), but (1+u/)-
See the detailed discussion in the memo: note that this is actually Student’s T.
DC2 workshop 28 June 05 - T. Burnett

5. DC2 workshop 28 June 05 - T. Burnett
Panel a: the PSF
It is normal incidence. I interpret it as the first bin in cos(), so <26 deg.
I evaluate in 2 bins per energy decade, using the Atwood function of the generated energy to scale the deviation
DC2 workshop 28 June 05 - T. Burnett

6. DC2 workshop 28 June 05 - T. Burnett
Panel a, cont.
Example of the results. The Atwood scaling function removes most of the energy dependence, but the shape depends on energy.
Each point is then rescaled back to degrees…
DC2 workshop 28 June 05 - T. Burnett

7. DC2 workshop 28 June 05 - T. Burnett
Panel a: the new result
DC2 workshop 28 June 05 - T. Burnett

8. DC2 workshop 28 June 05 - T. Burnett
Panel a: a footnote
Do the 68% (and 95%) values correspond to the simple analytic function?
DC2 workshop 28 June 05 - T. Burnett

9. DC2 workshop 28 June 05 - T. Burnett
Panel b
This must include the background-suppression cuts, but that is somewhat science-dependent.
The cuts actually introduce a “wart”. We expunge this!
DC2 workshop 28 June 05 - T. Burnett

10. DC2 workshop 28 June 05 - T. Burnett
Panel b
Points are measured for 0-26 degrees, adjusted by 4% to account for drop
Lines are simple “logistic function” representations
DC2 workshop 28 June 05 - T. Burnett

11. DC2 workshop 28 June 05 - T. Burnett
Panel c
This is slightly energy dependent. Don’t know what was used here, I’ll take the results for 1000 GeV, front+back.
DC2 workshop 28 June 05 - T. Burnett

12. DC2 workshop 28 June 05 - T. Burnett
Panel c
Curve is a simple linear (in cos theta) fit with two segments
DC2 workshop 28 June 05 - T. Burnett