Silicon Detectors and DAQ principles for a physics experiment

Silicon Detectors and DAQ Silicon Detectors and DAQ principles for a physics principles for a physics

experimentexperiment

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


Everyone wants to be noble !!!

Water is a good example….


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 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 voltageVbr

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!


Sampling Quantization


channels


In this world…..

….this is poker !!!


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?

Charge Timing Rates

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

MPPCSignal 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

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

QQ

AAQQ

preamp

tote

preampetot

195

12

det

det

103,1105105,7

105

Is the result ok?errors…..

st

VV

tR

VV

R

tQ

9

3

22

22

105

105

22

CQ

CQ

e

19

12

103,1

106,1

Huge errors due to the big error estimation on measured values of t and V

Can you do it better ???

Silicon Detectors and DAQ principles for a physics experiment

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