Dark Matter detectors -...
Transcript of Dark Matter detectors -...
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Dark Matter detectors
Andrea PossematoFinal report
25 September 2015Supervisor : Gustavo Cancelo
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Introduction
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We know only a small part of the universe !
DAMIC : “Dark Matter In CCDs”
Damic uses CCDs originally developed for the camera of the Dark Energy Survey.The detectors can record snapshots of the electric charge that would be created if a dark matter particle were to collide with the detector material inside a CCD.
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CCD as detector
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CCD : Charge Coupled Device● A CCD is a light-sensitive detector. It consists of a matrix of detectors (pixels).Each pixel accumulates an electrical charge depending on the amount of light falling upon it● Although A CCD is a light-sensitive detector, using the photoelectric effect it can also detect charged or uncharged particles by other physical effects such as compton, electron scattering, electron or nuclear recoil, etc
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How our detector works
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● Incident particles produce ionization in CCD bulk.
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The SETUP
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MONSOON
Master CPU Board
Clock Board
Video Board
“Panview” software
CCD
Vacuum pump
Cooling system
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Our SETUP : Photo (SIDET : ”CCD Research and development laboratory”)
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Camera CCD
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● Our CCD has a resolution of 8 Megapixel (4096 rows x 2048 columns)
Reset pulse
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Monsoon system : acquisition board
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Analog front endCCD signal
ADC
● Amplifier● Integrator● Performs CDS (Correlated Double Sampling)
FPGA
cds i=1T ∫0
T
[Datai(t)−Ref i(t)]dt cds i=1T
[∫t 3
t 4
xi(t )dt−∫t 1
t 2
xi(t)dt ]
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Digital correlated double sampling
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cds i=1N s
[∑ns
pixel i(ns)−∑ns
pedestal i(ns)]
● Take N samples of the pedestal and the pixel values during the observation time T● Digital Signal Process the data● Apply a digital CDS to the processed data
GOAL : Substitute the analog integrator with a digital system which implements CDS in an FPGA.
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FPGA SETUP
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Xilinx ML605
FNAL/ESE 8 channel A/D low noise board
● Xilinx ML605 evaluation board with Virtex-6 XC6VLX240T-1FFG1156 FPGA
● Analog to digital converter board developed by FNAL and ESE
● Low noise● 8 Channels● Fs : 2.5 MHz● 24 bit● FIR filter
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Data analysis
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● Analyze the digitized CCD signal with Matlab. ● Recognize “pedestal” and “pixel” values.● Measure pixels value by digital correlated double sampling method. ● Calculate and plot the standard deviation of pixels for several integration time values.
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Standard deviation and noise
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1/f noise
● 1/f noise or “pink noise” is often the S/N limitation to achieve lower energy detection in cosmology and other areas of physics and engineering.●Digital signal processing beyond CDS can improve noise below 1/f limit.
Minimum
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Noise measurement
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● Gain of the electronic system : 13.2 [next slides]
1/f noise
Minimum
Minimum value :~ 25 ADU for 45 samples.
Noise≈2513.2
≈1.89electrons
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Processed image in Matlab
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Overscan
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X-ray calibration
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● The current CCD technology does not permit accurate measurement of small charge units.● We use an alternative calibration : x-ray illumination with Fe-55 source, placed in front of CCD.● The high energy of x-ray is absorbed by silicon and multiple e-h pairs are generated.● In contrast to the visible light case, the electrons are generated in a very small cloud diameter.
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X-ray image and clustering
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● Group the bright pixels in clusters.● Calculate the total energy for each cluster.● Make an histogram of clusters energy.
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Histogram and gain
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Kα= 2.13e4 ADU
Kβ= 2.35e4 ADU
Kα
Kβ
Kα[FE-55]= 1620 e-
Kβ[FE-55]= 1778 e-
Gain'=2.13e41620
=13.15
Gain' '= 2.35e41778
=13.22
Gain≈13.2ADUelectron
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Noise consideration
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● In our CCD the image is only transferred into one of the two horizontal registers.● In the other amplifier there’ll be only the noise of CCD.
The noise of the two channels are correlated !
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Two channels acquisition (data and noise)
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Image noise improvement
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Thank you