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  

Experimental requirements

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

Working principles of the SDD

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

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

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

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

Performances of the SDDs

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

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

Resolution in the line shift measurement

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) 150 K 5.9 keV line PIN Tsh=20us Si(Li) Tsh=20us SDD Tsh=1us

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

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

Background reduction

Timing with the anode signal hn IK IA hn t IA tdr max

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

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

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

Signal/Background with CCD ·    Actual value of the S/B ratio measured with DEAR at DANE using CCDs S/B  1/100 in kaonic hydrogen expected: S/B  1/500 in kaonic deuterium

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

Reliability of the detection set up

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

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

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.

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 2003 - October 2003

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

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