Diapositive 1

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.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) Tkr1EndPos0,, Tkr1EndDir0,(end of
track)
CsILength326 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
start of track
4 GeV
end of track
muon sl10.5 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 219041 triggering evts, 303191 valid
hits
valid hits
total
ltEgt13.60 MeV
0.2 of valid hits have no energy.
doubles
ltEgt21.87 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)
high
low
light tapering
15
Valid events for calibration
These values correspond to a period of 4000 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)
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.
( 350-100250 )