GLAST Calorimeter Crystal Position Measurement

Zach Fewtrell, NRL/PraxisGLAST Integration & Test Workshop

SLACJuly 14, 2005

Data Set

4 TOWER DATA, ZERO SUPPRESSED

~600K events

~3K hits per cal xtal.

-All values extracted from SVAC tuple files.

- Runs 135002769 - 135002780

Software Environment

TRACK EXTRAPOLATION & CUSTOM TUPLE GENERATION

- Compiled C++ using ROOT libraries.

- Based on David Smith's/Benoit Lott's anaMeritNtuple.C

- More inclusive of partial xtal hits.

TUPLE ANALYSIS & PLOT GENERATION

- ROOT interactive.

Plan of action

1 – Retrieve main Tracker track position & vector at end

of track.

2 – Using LAT & Cal geometry constants, extrapolate

track into the Z-center of each Cal layer.

3 – extract cal xtal hit info for appropriate crystal.

4 – calculate longitudinal component of tkrPos – calPos.

5 – ‘diff’ is the main variable I study.

Initial cuts1 – TkrNTracks > 1

2 – Track can cut tower boundary, i skip layers where track crosses the

boundary.

3 – Partial hits allowed, but I only measured the hits which contain the

middle of the track.

- in any given layer, this should be the strongest hit.

- mostly driven by lack of desire to write more code, plenty of

partial track-hits already included.

4 – cal has to have a readout (ene > 0) duh!

Step 1: Xtal Ends

- Tracker extrapolated pos -vs- Cal Recon xtal pos

- scatter plot of all xtal hits..

- Cal clips xtal pos to CsI length, you don’t see the matching tails. This

adds bias to cal recon pos near xtal end.

-- NOTE: This effect is probably less w/ high energy showers.

- FIRST CUT: tkrPos > 23-28mm from xtal end

- SECOND CUT: calPos > 3mm from xtal end

Step 1: Xtal Ends

Step 2: CalTkr Diff –vs- energy

Step 2: Diff –vs- ene sigmas

X

XX

Error from pedestal noise.(back-of-envelope)

Step 2: Diff –vs- ene

1 – Position sigmas at low energies < 10 MeV per xtal

consistent w/ propagated pedestal sigmas.

2 – plots from now on are cut at xtal ene > 7 MeV.

All Crystals: Diff -vs- xtal index

Distribution of single channel mean difference

Distribution of single channel sigmas- consistent w/ other studies.

Distribution of reduced 2

Worst case channel T4 L7 X10

Best Case T1 L3 X10

Typical Channel – T0 L1 X10