Silicon Detectors and DAQ principles for a physics experiment
Telescopes
Human eyes
Microscope
Accelerators
Detectors
But where does it all start from?
Electronic properties of materials Atoms are made of proton, neutrons (nucleus) and electrons Valence and conduction electrons are responsible for the principal characteristics of different atoms
Electronic properties of materials Everyone wants to be noble !!! Water is a good example….
Electronic properties of materials Atomic levelsMolecular bands
If some electron is promoted in the conduction band, what may occur? 1)Drift: an external field can move these electrons 2)Multiplication; if the field is strong enough 3)Recombination: if nothing happens, electrons fall back to valence band What happens then? How can we describe the situation?
Physicians must be smart and clever…. holes !!! h+h+ h+h+ h+h+ h+h+
....and do a smart use of drugs!!! n dopingp doping Why ?
p-n Junctions Fermi level definition Electrons and holes diffusion Non equilibrium situation Donors and acceptors ions field plays against diffusion and equilibrium is reached Equilibrium !!! … ?
p-n Junctions Equilibrium is reached when the two Fermi levels are at the same energy A sort of slope is then created, hard to climb up and easy to roll down! Equilibrium does not mean immobility!!!
p-n Junctions Breakdown voltage V br Junctions are the basic devices for all semiconductor detectors! V=RxI
Particles through matter How can we detect them?
Particles’ measurements A particle passes through a silicon thickness, generating e-h pairs e - and h + are collected by anode and cathode (be aware of recombination…) An electric field causes electron flow through the device and created charge can be collected (by capacitor for ex.)
SDD, a clever anti- recombination device An electric field leads electrons, generated by particle flow (x- Rays or ionizing) to a small collector anode. At the same time holes are immediately removed from electron’s path by cathode strips.
Position measurements: strips !
We got the charge... and now what?
Analog – Digital conversion Digital signal; signal is a function of discrete numbers, F(N) Analog signal; signal is a function of continuous numbers, usually time, F(t) The world is analogic but Pc and analysis software can only work with digital informations….. Analog signal have to be converted to digital signals!
Analog – Digital conversion SamplingQuantization
Analog – Digital conversion channels
Analog – Digital conversion In this world….. ….this is poker !!!
Analog – Digital conversion Converting analog signals into digital signals, some information may be lost … but are they really necessary?
From analog signals to files and histograms: Data AQuisition methods
DAQ What are we interested in ? Which information can we get? ChargeTimingRates
DAQ : Discriminators
DAQ : QDC (charge to digital converter) QDC values (integer numbers) Histograms
DAQ : TDC (time to digital converter)
DAQ : Scaler 4 events in 10 seconds Rate = 0,4 Hz
A real example!
MPPC (Multi Pixel Photon Counters) detectors Each pixel acts like a p-n junction Breakdown current is used Output signals are summed
MPPC (Multi Pixel Photon Counters) detectors
MPPC Signal coming out from the detecor is then: QDC spectrum is then composed by several pixes with fixed distance
New physicists? Questions?
An experience in the lab: e - charge estimation
Ohm law Current definition Charge definition
b (time) h (Volt Ω)
Is the result ok? errors….. Huge errors due to the big error estimation on measured values of t and V
Can you do it better ???