1. Assessment and Proposal W. B. Atwood UCSC, April 6, 2005

2. GLAST Phase Space Science Requirements: Field-of-View (FoV) > 2.5 str. (or -1. < cos(  ) < -.2 ) Energy Range 20 MeV 300 GeV Instrumental: Conversion location: 1-of-16 Tracker Layers (Thin & Thick) Shower Location: Cal Module Edges Other: High energy, side entering events... GLAST PHASE SPACE IS VERY LARGE Consequence: unlikely that one energy correction algorithm will cover all aspects optimally Several techniques being pursued: Parametric, Last Layer, Profile,...

3. Current Situation Source: 1 GeV  's at near vertical incident at the ~ center of a CAL module Parametric Last Layer Similar resolutions – how to select which to use?

4. Proposal: Use Classification Trees GEnergy = CT-predicted-best-of Parametric, Last-Layer The CT selected energy is significantly better then either Parametric or Last-Layer in isolation. The CT mechanism allows us to mutually benefit in that region of phase space where one Algorithm works better then the others Can easily be extend to an arbitrary number of algorithms LL:Para – 50:50

5. Phase Space Breakdown 4 Bins in CalX0 4 Bins in cos(  ) Overall All Energy resolution at 1 GeV

6. Implementation The mechanism of Classification Trees can allow is to take the "best" solution across GLAST Phase-Space Structural Implications - CalRecon needs to calculate (or attempt to calculate) all solutions for each event (This is needed so that all the algorithms can be tested and monitored). - Top (or near top) Level Algorithm then uses a CT to select "optimal solution" which is presents to the user