1. Analysis of LumiCal data from the 2010 testbeam
Itamar Levy
Tel Aviv University
Belgrade, Serbia
September 2011

2. Introduction 2
In the summer of 2010 the FCAL collaboration had the first test beam measurement of the Lumical silicon prototype, and of the BeamCal GaAs.
In these measurements the full readout chain including silicon sensors, kapton fan-out and front-end electronics were tested.
An external CAEN VME-V1724 ADC was used. It is a 14 bits 8 channels 100Msp/s pipeline ADC controlled by computer via an optical link.
2 area of the silicon sensor have bean measured, 8 upper pads and 8 bottom pads.
During the beam test the response of readout chain to electromagnetic showers from tungsten absorber was also studied
The sensor board and the electronic board
The silicon sensor with 8 upper pads and 8 bottom pads measured. 2

3. Test Beam Set Up 3
100 mm
163 mm
250 mm
ZEUS telescope planes
Sensor box
Sensor
pcb
Trigger scintillators
4.5Gev electron beam
external
ADC
Telescope DAQ
coinc.
unit
trigger
busy
Test beam took place in beam line 22 of DESY II ring in Hamburg with 4.5 GeV electron beam. Measurements are the combination of our sensors, ZEUS telescope for position reconstruction and temperature monitoring.
The Telescope composed of 3 modules.
Each module have 2 single-sided Perpendicular Si planes (32 x 32 x 0.3 mm) with 640 strips/plane of 25 um pitch. The Readout pitch is 50 um.
The DAQs receive a trigger signal from the Telescope 3 scintillators via coinc. unit. The slower DAQ (Telescope), generates a “busy” signal, to level the events between the DAQs. 3

4. Spectrum analysis : one event4
In each trigger all 8 channels are recorded, with 128 sample points.
In the legend of figures 1semple1sample 4

5. Spectrum analysis : number of events5
When looking at number of events:
Baseline fluctuation (RMS ~15-20 ADC counts).
Noise correlation between channels is observed. 5

6. Spectrum analysis : S/N6
Integration window
To analyze the spectrum, the complete data set was taken. ~ 1Mevents for upper pads and ~1.2Mevents for bottom pads. Only 1/8 is in signal area of spectrum.
For spectrum different methods tried:
“spectrum” – integration within the Integration window of signal minus baseline.
“spectrumNB” – integration within the Integration window of just signal.
“generalspectrum” – integration in the full range (128 points) of just signal.
“amplitude” – the max amplitude of the signal minus the baseline.
“amplitudeNB” – the max amplitude of the signal.
We define S/N as :
To complete the measurement, the spectrum was fitted by an Gauss-Landau convolution.
Baseline 6

7. Spectrum analysis : S/N7
The calculated S/N for all channel :
Better not to use baseline subtraction:
Please round-up the numbers to at most two digits!!! 7

8. Spectrum analysis : S/N8
Only in the bottom pads we can see temperature difference in the data set.
The difference in the mean value of the pedestal is ~20ADC counts/1°C for all channels.
Y-axis legend ‘padastal’  ‘pedestal’ 8

9. Noise correlation 9
To check noise correlation we calculate for every 2 channels, the correlation coefficient, in pedestal events,
where S is the sample and σ is from the 128 samples in one channel in event.
For each pair, we got a distribution between -1 to 1 of the correlation coefficient.
The correlation coefficient MPV is presented.
X-axis legend, ‘correlation factor (arb. unit)’  correlation coefficent
By construction, there are no units for the correlation coefficent !!! 9

10. Cross-talk Point by Point correlation ch0 and ch1 Profile Y axis10
Point by Point correlation ch0 and ch1
Profile Y axis
To see the noise correlation we make a Point by Point correlation 2D graph for each pair of channels. Each graph contains ~128M samples (1M events times 128 samples each).
We try to estimate cross-talk coefficient by using the ROOT profile tool, and study the behavior of the mean value of the pedestal as function of signal size in the other channel.
We can also see that the cross-talk coefficient is getting bigger at very large signals > ~6MIP
Profile X axis 10

11. Cross-talk 11
The cross-talk coefficient was normalized by the ratio between the amplitude MPV’s of the signal.
We can see that the cross-talk coefficient of the bottom pads is more then twice the coefficient in the upper pads, due to the long transition lines to the ASICs
Normalized cross-talk coefficient – bottom pads
Normalized cross-talk coefficient – upper pads 11

12. Cross-talk 12
The cross-talk coefficient was normalized by the ratio between the amplitude MPV’s of the signal.
We can see that the cross-talk coefficient of the bottom pads is more then twice the coefficient in the upper pads, due to the long transition lines to the ASICs
Normalized cross-talk coefficient – bottom pads
Normalized cross-talk coefficient – upper pads 12

13. Time stamping 13
In this testbeam the time stamping was critical since one needs to match between events in sensor DAQ and in Telescope. We rely on the trigger/busy logic and low rate of event at 4.5 GeV to determine that the two systems have the same number of events. Then by shifts in small number of events one can match, and use all of the data.
Position reconstruction was made with track that hit only 1 time per plane of telescope. reconstruction efficiency is ~50%
Position reconstruction with correct shifts +1
Position reconstruction with correct shifts
Position reconstruction with correct shifts
In this plots every color is for one channel over threshold
Position reconstruction of bottom pads
Position reconstruction of upper pads 13

14. Charge collection uniformity14
As a start of the study of charge collection uniformity of the sensor, position reconstruction data combined with spectrum analysis.
Each reconstructed event got a weight of his integrated charge normalized to the MPV of the signal in that channel. We averaged the combined charge by the number of hits per area (since the beam profile is not uniform).
In this measurement we got around hits per square mm (half in the upper pads) .
One can see that in the pads the charge collection is uniform (plus some edge effects). There is decrease of charge collection of ~10% of 0.2 mm around the 0.1 mm gaps between pads
Sensor uniformity upper pads
Sensor uniformity bottom pads 14

15. Summary 15
We present here some new results from the 2010 LumiCal testbeam.
S/N – measurement of spectrum using the max amplitude can give S/N of up to 20, by measuring the total signal (without any subtraction) this level of S/N and higher can by achieved. It is difficult to use this kind of measurement since the baseline of the signal has temperature dependence of ~20 ADC count/°C .
Noise correlation – in this data set a high noise correlation coefficient is observed.
Cross-talk – by using the profile of correlation graph an estimate of cross-talk coefficient can by obtained. The estimate suggests a cross-talk coefficient of the order of 1% for the short lines and 3% for the long lines.
Charge collection uniformity – first result shows that there is uniformity in the pads and between similar pads, there is same decrease in the uniformity in the small gap between pads.

16. Supplement 16 16