1. PreShower Characterisations
Pulse shape study with a cosmic bench
Test beam results
Set-up
Pulse shape characteristics
Dependence on pulse height
Pedestal stability
Photoelectron statistics
Dispersion of PMT gains
Effects of HV changes
Half-channel relative gains
Uniformity in a cell
Cross talk
Additional cross talk studies
Cell to cell cross talk
Electronic cross talk

2. Pulse shape study with a cosmic bench
Set-up
16 cells of 12 12 cm2
3 m clear fibres
Mono-anode R5900 PMT
RC = 100   50 pF = 5 ns
Results
0 ~ 70 % (i = Si / STOT )
65-75 % according to channel
For maximal 0 : -1 ~ 1-2 %
Main exponential decay  ~ 9-11 ns according to channel
RC non negligible
Affects pulse raising time
Small long term component  > 200 ns
Perhaps delayed fluorescence
Non negligible beyond 50 ns

3. Test beam set-up 16 cells of 12 12 cm2 80 cm WLS fibres
3 m clear fibres
64 multi-anodes PMT
64 channels VFE prototype
Load resistors : R = 150 
Readout capacity : C ~ 10 pF
RC ~ 1.5 ns
22m Ethernet cables
16 channels FE prototype
1 V  1000 ADC counts
First time used in test beam
Time jitter of 3.5 ns (min to max)

4. Pulse shape characteristics
100 GeV Pions / no lead / HV = 800 V
Scan integration time from 0 to 24 ns
Similar responses for all channels
Time position of maximal 0 within ± 1 ns
Non zero -1 for maximal 0
Slight discontinuity at replication time
Integrator dead time ~ 1 ns
Effective integration time ~ 24 ns
In Ernest Simulation
For maximal 0
0 higher of ~ 7 %
1 in agreement
2 lower of ~ 3 %
3 lower of ~ 2 %
Long term component only in data

5. i distributions ? No peak at 0 for 2 and 3
The 0 photoelectron peak is at 0 in the simulation
Not in data : pedestal shift ? ?

6. i values Compatible with cosmic bench  = 1 / 0  [15.6 % ; 22.5 %]
Lower RC  Higher 0
 = 1 / 0  [15.6 % ; 22.5 %]
Min (%)
Max (%)
Mean(%)
-1
0.2
1.0
0.4 0
68.9
76.7
73.6 1
12.0
15.5
13.8
2 HIGH
4.0
7.6
6.0
2 LOW
2.3
2.9
2.6 3
1.3
2.0
1.7

7. Long term component : pedestal shift ?
< 6 > = 0.83 %
6 distribution : pedestal shift rather than delayed photoelectrons
Also seen with LED on one cell
Pedestal shift on other channels  here -1 ADC count (worst case)
No PM cross talk
No PS cross talk
Not the same chip

8. Pulse shape dependence on pulse height
Look at  and  variations with pulse height (NADC)
To change pulse height
Change HV keeping MIP signal
 and  are constant
Change signal using electrons keeping HV
 increases and  decreases (almost linearly)
The effect is coming from the PMT
Studied as a function of the maximal PMT output current (output current for 100 MIPs)
Electron data for various HVs
100 MIPs
100 MIPs

9. Pulse shape dependence on pulse height (2)
The maximal variations of  and  other the full dynamic range are respectively
100 MIPs - MIP
100 MIPs - MIP
These maximal variations depends almost linearly on the output current at 100 MIPs
Limiting to 1 mA leads to a maximum of 6 % for both  and 
Should be lower with the new PMT basis m m

10. Pedestal Stability 8 hours measurements Mean pedestal
ADC counts
8 hours measurements
Mean pedestal
Stable within  0.1 ADC counts
Noise ~ 0.7 ADC counts
Stable within  0.05 ADC counts

11. Photoelectron statistics
Measure of the number of photoelectron / MIP
Using only MIPs
NPE / MIP = (MIP / MIP ) 2
Scaling MIPs to a large LED pulse
LED distribution has a gaussian shape
NPE / MIP = NPE / LED  (MIP / LED )
Compatible results obtained with the two methods
100 GeV Pions / no lead / HV = 800 V
LED / HV = 800 V

12. Number of photoelectrons and PMT gains
< NPE / MIP > = 15. 3
From 10 to 20
PMT gains for the different channels
GMAX / GMIN = 2
HV changes
The different channels should have the same behaviour (to preserve uniformity)
Checked on 4 cells
G750V / G650V  7
G650V / G550V  7

13. Half-channel relative gains
Odd/even half-channels
Gain differences ~ 5 %

14. Uniformity in a cell • PS CELL 50 GeV Pions 49 measurement points BEAM1 2 3 4 5 6 7 8 9
PS CELL
50 GeV Pions
HOR  1 cm
VER  1.6 cm
Muon contamination  1 % (  10 cm)
49 measurement points
Each 2cm (horizontal  vertical)
RMS of pool distribution = 1.35
Pool distribution with a RMS of 1 introducing a non uniformity of (1.3  0.6) %
BEAM

15. Uniformity in a cell (2) Pool distribution is gaussian
No obvious behaviour on a 2D analysis
Pool distribution measured assuming 1.3 % of non-uniformity (49 entries)
Gaussian ( = 0 ;  = 1 ; 49 entries)
2  cells

16. Cross talk 100 GeV electrons Beam on cell C12
 2.5 % of cell to cell cross talk
Total PMT cross talk  18 %
Channel repartition depends on mask set up
Up to 6.4 % (4.3 %) in June (August)
Globally, ¼ of the light is lost by cross talk
From 20 to 15 photoelectrons per MIP

17. Cross talk results PS PMT BEAM June August (August) C13 2.4 C15 1.5
3.4
C14
2.0 C9
1.6
C11
3.7
C12
100
C10
2.2 C6
1.2 C8 C7 C5
0.8 C2
0.1 C4
6.4 C3
0.4 C1
1.8
C13
2.9
C15
1.7
C16
2.5
C14
4.0 C9
1.5
C11
3.2
C12
100
C10
2.4 C6
1.1 C8
1.9 C7
2.2 C5
0.9 C2
0.2 C4 C3
0.4 C1
4.3 PS
BEAM
June
August C7
2.4 C6
1.2 C3
0.4 C2
0.1 C8 C4
6.4 C9
1.6
C11
3.7 C1
1.8
C12
100
C13
C10
2.2 C5
0.8
C14
2.0
C15
1.5
C16
3.4 C7
2.2 C6
1.1 C3
0.4 C2
0.2 C8
1.9 C4
1.7 C9
1.5
C11
3.2 C1
4.3
C12
100
C13
2.9
C10
2.4 C5
0.9
C14
4.0
C15
C16
2.5
PMT
(August)

18. Cell to cell cross talk In Clermont cosmic bench
Light coming from a LED
Installed very carefully on the cell surface and very well isolated so that there is no light leakage at the LED level
Dedicated PMT mask to read only one fibre with the mono-anode R5900 PMT
No cross talk at PMT mask
~ 2 % cell to cell cross talk measured
Compatible with test beam results

19. Electronic cross talk Set-up Result
Reproduce all the electronic chain from the output of the PMT to the input of the FE board
Result
Up to 1% cross talk between neighbouring channels at VFE output
Where does this cross talk come from exactly ?
To be investigated
Not from the chip : already measured in standalone mode (cross talk ~ few ‰)
Better with the new VFE board ?
Perhaps because smaller 10 9 19 17 18 26 25 27 f8
100 f7
0.3
1.0 f6
0.7 f5 f4 f3 f2 f1