1. DEAR SDD --> SIDDHARTA
Silicon Drift Detector for Hadronic Atom Research and Timing Applications
Carlo Fiorini
(Politecnico di Milano)
Development of a soft X-ray detection apparatus,
based on Silicon Drift Detectors (SDD),
with high energy resolution
and high background reduction
for application in exotic atoms researches

2. Experimental requirements

3. Experimental requirements
Exotic
atom
e.m. position
of K line
(keV) 
(eV) 
Required precision
 (eV)
 (eV)
hydrogen
6.46
 160
 200
~ 5
~ 10
deuterium
7.81
 500
 800
~ 25
~ 100

4. Working principles of the SDD

5. The classical PIN diode detector
The anode capacitance is proportional to the detector active area

6. The Semiconductor Drift Detector
The electrons are collected by the small anode,
characterised by a low output capacitance.
Anode
Advantages: very high energy resolution at fast shaping times, due to the small anode capacitance, independent of the active area of the detector

7. The Silicon Drift Detector with on-chip JFET
JFET integrated on the detector
capacitive ‘matching’: Cgate = Cdetector
minimization of the parasitic capacitances
reduction of the microphonic noise
simple solution for the connection detector-electronics in monolithic arrays
of several units

8. The integrated JFET
Detector produced at the MPI Halbleiterlabor, Munich, Germany

9. Performances of the SDDs

10. Silicon Drift Detector performances
Quantum efficiency of a 300 mm thick SDD
55Fe spectrum measured with a SDD
(5 mm2) at –10°C with 0.5 ms shaping time

11. Silicon Drift Detector Droplet or SD3
T=-30°C a τsh=1µs
Canode= 50 fF
(vs. 100fF conventional SDD)

12. Resolution in the line shift measurement

13. Spectroscopic resolution: detector comparison - 1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 1
100
200
300
400
500
600
700
800
A (cm-2)
FWHM (eV)
SDD PIN Si(Li) K keV line
PIN Tsh=20us
Si(Li) Tsh=20us
SDD Tsh=1us

14. Spectroscopic resolution: detector comparison - 2
FWHMmeas of monoenergetic emission line 5.9 keV
1cm2 detector at 150 K
SDD FWHM=140eV tshap =1ms
Si(Li) FWHM=180eV tshap =15ms
PIN diode FWHM=750eV tshap =20ms
CCD FWHM=140eV tframe=1s

15. Measure of the line shift – ideal case *
The case: kaonic hydrogen, 200 cm2 detection system For 6000 events (~ 50 pb-1 )
Estimated peak position 6.3 keV, line width about 245 eV, peak shift about 160 eV Detection system based on SDDs
* No background contribution considered

16. Background reduction

17. Timing with the anode signalhn IK IA hn t IA
tdr max

18. Timing resolution with SDD
A=0.1cm2  Tdrift = 70ns
A=0.5cm2  Tdrift =350ns
A= 1cm2  Tdrift =700ns
With:
r = 2kW/cm
H = 450mm

19. Triggered acquisition
Kaon trigger
Concidence windows
Detected pulses
Considered pulses
X-ray pulse
Background pulse
tdr max

20. Background reduction with triggered acquisition
r =number of detected kaons per detected X-ray = 103 Br=background rate = 103 events/s
Tw=sinchronization window
Tw = r x t drift max = 103 x 1 ms = 1ms
B = Br x Tw = 103 s-1 x 10-3 s = 1
S/B = 1/1

21. Signal/Background with CCD
·    Actual value of the S/B ratio measured with DEAR at DANE using CCDs S/B  1/ in kaonic hydrogen
expected:
S/B  1/ in kaonic deuterium

22. tdr max Timing with the prompt signal from the backplane hn IK IA hn t
Estimated time resolution: about 300 ns

23. Reliability of the detection set up

24. Monolithic array of Silicon Drift Detectors
Pixel area = 5 mm2
Total array area = 95 mm2

25. DEAR test setup (SDD) at the BTF
BTF e+/e - beam
e+, e – g
shower
Pb plate
Ti foil
Zr foil
SDD X-ray detector
(4 chips prototype)
Pb shielding S2
X-ray lines S1
scintillators

26. Operations:
The first stage of the project of the new detector deals with the characterization of the SDD performances.
The characterization concerns the finalization of trigger efficiency and energy resolution, as a function of background environment and time window. This information will fix also the dimension of the single cell. These measurements are planned to be performed with a prototype device. The answers coming from these tests will be used for the construction of the final detector array and associated electronics with optimal characteristics.

27. Beam conditions at BTF: BTF run period required:
Energy: varying between 50 ÷ 750 MeV
Intensity: varying between 1÷ 103 e+/e- s-1 (preference is for positrons)
tbunch :  10 ns; bunch frequency: 1 ÷ 49 Hz
Gate window 0.1 – 1 ms
BTF run period required:
2-4 weeks in the period June October 2003

28. The detector: 1 cm2 SDD prototype
Front-side: field strips, JFET
Back-side: entrance window
65 rings, 1 cm2 area
280mm high-resistivity + 12mm epi-layer
detector presently under test at Politecnico di Milano

29. Preliminary measurements
Leakage current ~ 3 room T
Voltage divider threshold voltage
~ -50V for 8 rings ( 65 rings bias
should be feasible with ~ - 400V)