1. Start Detector for pion experiments
Jerzy Pietraszko, Wolfgang Koenig
and
Lukas Chlad, Stefano Spataro, Michael Träger, ...
Outlook:
Detector requirements:
time resolution,
compact design, vacuum operation
segmentation, rate capability,
fast signals for trigger fun
Detector construction:
solid target version
LH2 target version
Diamond detector for MIPs
operation principles
expected performance
Performance during the pion beam time (2014)
Future plans
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

2. Pion beam Start Detector requirements
Trigger for beam pions hitting the LH2 or solid state target
Area about 1.5 cm x 1.5 cm, operation in vacuum
Located close to the LH2 target -> very low power consumption of the electronics
Hit rate capability up to 107cm-2s-1
Low material budget to minimize the load on the RICH photo-electron detector
Reasonable position resolution (sigma) < 1 mm  beam profile for beam monitoring
Time resolution < 100 ps (sigma)  used as T0 detector and in trigger system
High efficiency for MIPS
 scCVD diamond material
background event
pion on LH2
33,5 cm
Start detector
2 cm
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

3. Pion beam challenges - target region
Very broad beam profile at the target
Massive holder of the LH2 target
Beam profile from pion experiemnt
 = 7.7 mm
1 %
 = 3.5 mm
Selective trigger system essential
M2 trigger – 75 kHz
M2 & Start – 9 kHz !!!
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

4. Detector construction and mounting – short version
(used in 2014 beam time)
33 cm
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

5. Detector construction and mounting – long version
(desined for LH2 target)
PCB and electronics design:
Low power design needed – close to the LH2 target. Limited space !
1st stage of amplification on the PCB
36 signal lines + HV + LV
LH2 Target
96.5 cm
33.5 cm
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

6. Expected detector performance
stable long term operation
time resolution below 100 ps ()
year 2010
 ≈ 117 ps
300V
150V
100V
 ≈ 90 ps
15 mV
year 2013
Two key conditions to achieve  below 100 ps:
bias voltage above 1 V / µm
signal to RMS noise ratio > 40
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

7. Performance during pion beam time
Unstable operation above 0.6 V / µm – too low bias voltage
Large pickup noise seen in the setup – Signal/RMS Noise ≈ 7
 Time resolution above 200 ps () – varies for different channels
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

8. Performance during pion beam time
Unstable operation above 0.6 V / µm – too low bias voltage
Large pickup noise seen in the setup – Signal/RMS Noise ≈ 7
 Time resolution above 200 ps () – varies for different channels
 unfortunately some channels shows double structure in ToT – walk correction not easy
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

9. Performance during pion beam time
Several target changes, different noise situation
 Time resolution above 200 ps () – varies in time for
different channels
Example: Time resolution for pions reconstructed in RPC
(RPC contribution not subtracted !)
Start channel 21
Start channel 14
time resolution [ns]
file number
file number
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

10. Needed improvements and preparation for LH2 target
Bias voltage stability under investigation, several diamond plates show this problem:
Surface effect
bulk material problem
metallization too close to the border (100 µm)
Full system noise performance tests:
Test of the setup with readout electronics
Beam test
Performance study (intensity, HV, time res. )
Long holder preparation (LH2 version):
Improvement on mechanical stability of the holder
Performance of the detector with long holder (noise)
Tests with LH2 target:
Installation inside the LH2 target (mechanics)
long term stability test: target ON, diamond ON
LH2 target status:
Target is fully operational, tested at GSI without beam.
Tested in Orsay (Tandem) with beam including heat dissipation expected from diamond detector.
Open question:
Can we measure with LH2 target and with short diamond holder ? Background ? – Simulation/data analysis from last pion beam time ?
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

11. J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015
Summary
Mosaic scCVD diamond detector operational and employed in 2014 (short holder version):
- excellent trigger performance demonstrated
- time resolution about 200 ps () – design value not achieved
- some channels show ToT spectra with double peak structure
- S/N ration of the full system not fully controllable (pick-up noise)
- Sustained dark current observed under radiation (bias voltage kept below 0.6 V / µm)
Long holder version for the LH2 target in preparation:
- 1 m long PCB holder ready, additional mechanical stabilization in development
- Mechanical integration with LH2 target
- Full system laboratory detector test – main focus on S/N
- Final test in HADES cave with LH2 target switched on.
Simulation study: can we use short holder for LH2 target ? What trigger performance we can expect?
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

12. J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015
backup slides
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015

13. Diamonds for high precision tracking - PADI for straw tube readout
beam test – Jülich, Feb. 2015
Michael Träger, Jerzy Pietraszko

14. Experimental setup DAQ /Trigger: Reference, tracking, scCVD detector
100 µm
4.3 mm
Straw tubes,
Φ = 6mm
p beam
4.3 mm
scCVD diamond
four channels – metallization
100µm space between electrodes
time resolution below 100 ps
attached to a movable table,
(µm step precision)
straw tubes connected to the PADI v6
straw diameter: 6 mm
Ar/CO2: 70%/30%
HV: 1800 V
DAQ /Trigger:
Oscilloscope used as a DAQ (R&S 1044)
correlated signal in two diamond electrodes used as a trigger
 proton in the 100µm gap between electrodes.

15. Experimental setup – diamond position resolution
Reference, tracking, scCVD detector
scCVD diamond signal for MIPs
100 µm
4.3 mm
4.3 mm
four channels – metallization
100µm space between electrodes
time resolution below 100 ps
attached to a movable table,
(µm step precision)
Used threshold: 7mV on each channel
 position better than 50µm
DAQ /Trigger:
Oscilloscope used as a DAQ (R&S 1044)
correlated signal in two diamond electrodes used as a trigger
 proton in the 100µm gap between electrodes.

16. Experimental setup scCVD diamond detector mounted on movable table
Straw tubes,
 = 6mm
p beam
scCVD diamond detector
mounted on movable table
angular alignment
straw <-> electrode gap
Real beam spot – Jülich beam time

17. Drift time measurement
Time difference between the scCVD diamond detector
and Straw Signal from the PADI discriminator.
 Drift time spectra (example for 5 positions)
+1.5mm
+2.0mm
+1.0mm
+0.5mm
+0.0mm

18. Drift velocity estimation

19. J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015
backup slides
J. Pietraszko, HADES Collaboration Meeting XXX, Lisbon , October 2015