1. Imaging crystals with TKR
Benoît Lott (CENBG)

2. Imaging the crystals
The information from the TKR can help investigate the CAL response in different
ways by:
mapping out the response as a function of the longitudinal and transverse positions
of the particle trajectory within the crystal: “images”.
cross-check of the light tapering (1D instead of 2D); non uniformity in response (see next
talk); possible local flaws.
enabling the determination of the trigger efficiency for the CAL;
checking the trajectories as determined from the CAL;
determining that the particle will leave significant “direct” energy in
the photodiodes;
- determining valid hits for the calibration: on-orbit calibration with heavy ions.

3. CRYSTAL IMAGING:
Plot the average measured energy as a function of trajectory position within the crystal.
The trajectory determined by the TKR must be extrapolated into the CAL and only “valid” hits are kept.
Trajectories must intersect the top and bottom faces of a crystal (no crossing of vertical sides).
At most 1 valid hit per layer.

4. The real question is how accurate is the extrapolation, as two adverse
effects come into play:
- the finite resolution of the tracker, the effect being amplified by the lever arm
between the Tkr layers and CAL;
- multiple scattering within the Tkr and CAL.
Tracker recon must provide the best estimate of the actual trajectory taking
two important facts into account:
1) the incident particle is a muon, not a gamma-ray;
The energy deposited in the CAL (~100 MeV) does not reflect the kinetic
energy.
jobOptions.txt:
TkrInitSvc.SetMinEnergy= 2000 MeV;
TkrIter.Members={};

5. 2) the final trajectory (i
2) the final trajectory (i.e leaving the tracker) is of interest here, not the initial one.
The track reconstruction algorithm was designed to determine the initial direction of photons. It makes use of the information available as close as possible to the conversion point, to avoid the adverse effect of multiple scattering.
For the present purpose, it is more sensible to use the information provided by the bottom trays:
end-of-track parameters (CalValTools or xxx_recon.root)
Thanks to Bill and Leon for their help.

6. Trajectory-extrapolation algorithm
Simple root macro, using modified (thanks, Anders) svac ntuple:
VtxX0,…,VtxXDir,… (start of track)
Tkr1EndPos[0],…, Tkr1EndDir[0],…(end of track)
CsILength=326 mm

7. « lTkr – ltrue » distributions
position evaluated at mid-height of first CsI layer
blue: start of track red: end of track
lTkr – ltrue (mm)
ltrue= true (MC) position in firts cal layer

8. Multiple scattering at play (1)
position evaluated at mid-height of first CsI layer for a pencil beam
l_Tkr_top
4 GeV l
l_Tkr_bottom
ltrue
position with respect to launch position (mm)
ltrue= actual (MC) position

9. Multiple scattering at play (2)
The effect of multiple scattering in the
tracker can be partly corrected for
by using the bottom parameters.
l_asym= actual (MC) position at first
calorimeter layer

10. Position resolution 4 GeV muon: sl=10.5 mm 500 MeV start of track
end of track
muon: sl=10.5 mm
500 MeV
start of track
end of track

11. Muon energy distribution
The tracker can help efficiently discard low-energy muons, associated with
large multiple scattering.

12. Position resolution
start of track
end of track
Lattest Svac tuple

13. Deposited-energy distributions
4M evts: triggering evts, valid hits
valid hits
total
<E>=13.60 MeV
0.2% of valid hits have
no energy.
« doubles »
<E>=21.87 MeV
2.9% (8791/303191) of hits have more than 2 MeV in a neighboring log. For these hits, the deposited energy in the « selected » log is much higher than average: emission of d electrons !

14. Images
width (mm)
length (mm)
width (mm)
low
high
light tapering

15. “Valid events” for calibration
These values correspond to a period of s (55 Hz at the trigger level).
top
bottom
tower 8
tower 9

16. How is it going to look like in real data?
asym
lTkr – lasym (mm)

17. Gsi data: protons at 1.7 GeV
X layers
Y layers
Simulation results
The width of the distribution of the residues of a linear fit is proportional to the resolution s:
0.55 s for the outer layers, 0.83 s for fhe inner layers (simulations).
X layers: s = 10 mm Y layers: s = 7 mm

18. To be continued…
A note summarizing these results will be written up with David Smith (SLAC).
This work will be extended with David, to apply it to real data.
The GAM( Montpellier) group will join us on some particular studies (comparison between trajectories determined by Tkr and CAL) .

19. MIPs in Photodiodes Same pre-amps, amps, adc, daq as for
Ganil, GSI, and CERN
(testbeam CsI stack at left…)
This is the outline of the talk: I will briefly remind you of the design of the LAT calorimeter, give its current status, show a few slides on the construction
Process, the present the status of the flight manufacturing. I then present the milestones along the way towards the delivery of the subsystem.
Then I talk about the identified threats to maintaining schedule and cost.
Smaller (top) scintillator:
2cm x 2cm
We also used:
A 2cm long “CDE”
A “naked” photodiode
(thanks to G. Bogaert for providing the latter)

20. Muons in a naked photodiode -- data
In the CDE we said
1 MIP ~ 12 MeV ~ 1300 dc ~ 1.3 volts
For the photodiode without CsI,
we see ~250 dc
Zoooooom….
( =250 )