how do we see particles? detectors and data acquisition for physics experiments
DESCRIPTION
How do we see particles? Detectors and data acquisition for physics experiments. Alessandro Scordo International Masterclass 2013 04/02/2013 LNF, Frascati. Telescopes. Human eyes. Microscope. Accelerators. Detectors. But where does it all start from?. - PowerPoint PPT PresentationTRANSCRIPT
How do we see How do we see particles?particles?
Detectors and data Detectors and data acquisition for acquisition for
physics experimentsphysics experimentsAlessandro ScordoAlessandro ScordoInternational International Masterclass 2013Masterclass 201304/02/2013 LNF, 04/02/2013 LNF, FrascatiFrascati
Telescopes
Human eyes
Microscope
Accelerators
Detectors
But where But where does does
it all start it all start from?from?
Electronic properties of materialsElectronic properties of materials
Valence and conduction electrons are responsible for the principal characteristics of different atoms
Electronic properties of materialsElectronic properties of materials
Everyone wants to be noble !!!
Water is a good example….
Electronic properties of materialsElectronic properties of materials
Atomic levels Molecular 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+
....and do a smart use of drugs!!!
n doping p dopingWhy ?
p-n Junctions
Fermi level definition
Electrons and holes diffusion
Non equilibrium situation
Donors and acceptors ions field plays against diffusion and equilibrium is reachedEquilibrium !!! … ?
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 voltageVbr
Junctions are the basic devices for all semiconductor detectors!
V=RxI
What and how What and how we measure?we measure?
Energy Time Rate
What and how we measure?Momentum (or energy???)
Position Tracks Mass (or energy???)Multiplicity
Measuring energy: Measuring energy: the Bethe Bloch formulathe Bethe Bloch formula
Particles through matterParticles through matter
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.)
A clever example: A clever example: Silicon Drift DetectorsSilicon Drift Detectors
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.
Measuring position: strip detectors
Measuring rate Measuring rate
Particle identification Particle identification via Time of Flight (TOF)via Time of Flight (TOF)
TOF can be used for measurements of mass, energy, momentum (velocity) of a particle (particle identification)
e-
-
-
Particle identification Particle identification via Drift Chamber (DC)via Drift Chamber (DC)
We can identify particles, measuring charge, mass, momentum; we can reconstruct vertices and parent particles
Measuring multiplicityMeasuring multiplicity
Signal coming out from the detecor is then:
QDC spectrum is then composed by several peaks with fixed distance
Measuring multiplicityMeasuring multiplicity
Quantization in your pocket:
e- charge estimation
areadtiQ
t
Qi
iRV
t
t
tot
1
0
Ohm law
Current definition
Charge definition
b (time)
h (Volt Ω)
2
hbQ
C
sV
R
tVQ
nst
mVV
tot12
92
1051052
1025102
2
)525(
)520(
CAA
AAQQ
preamp
tote
preampetot
195
12
det
det
103,1105105,7
105
Is the result ok?errors…..
st
VV
tVVtARA
Qpreamp
e
9
3
2222
det
105
105
2
1
CQ
CQ
e
e
19
19
103,1
104,0
30 % error due to the big error estimation on measured values of t and V
We got a signal...We got a signal...
and now what?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
Sampling Quantization
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 : 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
New physicists?
Questions?