Particle Detectors - Forschungszentrum Jülich

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Lecture

9


PARTICLE DETECTORS

Detlev
Gotta

Institut für Kernphysik, Forschungszentrum Jülich / Universität zu Köln


GGSWBS'12
, Batumi, Georgia

5th Georgian
–

German School and Workshop in Basic Science

August 16, 2012

Folie
2

EXAMPLES OF COMBINED DETECTION SYSTEMS

HOW TO DETECT?

INTERACTION OF CHARGED PARTICLES WITH MATTER



“ MASSIVE NEUTRAL PARTICLES WITH MATTER




“ RADIATION WITH MATTER

DETECTOR PRINCIPLES

WHAT TO DETECT ?

Folie
3

WHAT TO DETECT ?

Folie
4

PARTICLES

Light












Heavy



p
article



detector


registration

Folie
5

PARTICLES

What

characterizes

a
particle
?



mass






M


charge






Q



Spin
intrinsic

angular
momentum


S


life

time




t
0



shape

(
for

extended

particles
)


<r
2
>



Folie
6

RADIATION

fluid





gas






„light“

fundamental
constant
: c =
speed

of

light in
vacuum

(


30⁣⼠
湳
)

Folie
7

RADIATION

What

characterizes

waves
?


wave

propagation

velocity


c =
ln

睡we

汥湧瑨




l

晲煵敮ey





n



灡牴楣汥

灨祳楣i


usually

electromagnetic

radiation




wave

propagation

velocity

in
vacuum


c =
l n


†
“ “


“
in
medium


c‘
=
l
‘
n

<
c

index

of

refaction




n = c / c‘


Folie
8

CONSTITUENTS OF MATTER I

a
toms


10
-
10

m



atomic

shells

nucleus




electron

proton

neutron



e p n




Q






1

††††
⬠ㄠ†††††††0


††††††
M

††


M
p

/ 1836

M
p






M
p





size


<
10
-
18

m


0.8


10
-
15

m




life

time
t
0

> 10
26

y
> 10
29

y

886 s




decay

-

-

n


p e


n


Folie
9

CONSTITUENTS OF MATTER II




pions


kaons

many

more


p
K …

Q


0,


1


††††††††††
㈠


0
Ⱐ


1


M




M
p

/ 7


M
p

/ 2


size


0.6


10
-
15

m 0.6


10
-
15

m

life

time

t
0


p


26

10
-
9

s
K



12

10
-
9

s




p
0

8

10
-
17

s

K
0
S,L

9

10
-
10

/ 5

10
-
8

s


decay


p




m



n K




m



n,
…


p
0



g
g

K
0



p

+

p


,
p

0

p
0

,...

new

particles

–

unstable

being

free

Folie
10

PARAMETERS


total
energy





rest

mass


m
0

≠ 0

range

in matter




=
0


attenuation

in
matter


charge


Q ≠ 0

deflection

in
el
.
-
mag
fields




= 0

no

deflection




life

time


t

=
gt
0

decay

length

l = v
t




=




relativistic

factor








massive
particles



el
.
-
mag.
radiation

0
m
total
E
kin
E
2
c
0
m
4
c
2
0
m
2
c
2
p
total
E



+

γ
kin
E
h
pc
total
E



ν









c
v
lim
c
v
,
2
1
1
γ
β
β
γ
h

Planck
constant


= minimal
action

Folie
11

HOW TO DETECT ?

Folie
12

FORCES

•
nuclear

force


keeps

protons

and

neutrons

together


•
electromagnetic

force

keeps

electrons

around

the

nuclei


•
weak

force



makes

the

(
free
)
neutron

to

decay


•
gravitation


keeps

us

on
the

ground

strength

Standard Model

Folie
13

ELECTROMAGNETIC FORCE


a
force

is

mediated




classical


picture





quantum

world



by

field

around

a
source




field

quanta

=
particles








„light“
particles

=
photons

g


2
2
1
0
Coulomb
r
Q
Q
4
1
F


πε
electromagnetic

radiation

= E
and

B
fields

interacts

with

electric

charges

Folie
14

DEFLECTION OF CHARGED PARTICLES IN EL.
-
MAG. FIELDS


•
electric

field





•
magnetic

field








B
v
Q
x
m
F
E
Q
x
m
F


















B =
const
.



circular

motion



B


plane
of

projection

T
2
B
M
Q
π
ω
ω


M
Q

r
B
Q
p
B
v
Q
r
/
mv
2






p

r

Folie
15

SIGNAL CREATION

•
via
electric

charges


•
measure

the

electric

current

I

or

voltage

U


resistor

R

U

I

c
apacitor

C

U

Q

Folie
16

INTERACTION OF


CHARGED PARTICLES


WITH MATTER

Folie
17








before




after
collision




1.

M
particle

1

>>
M
particle

2








2.

M
particle

1

=
M
particle

2




CHARGED PARTICLES

interaction

happens

by

collisions

of

particles

type 1
and

2

Folie
18

CHARGED PARTICLES I: ENERY LOSS BY COLLISIONS

1.


M
particle

>>
M
electron





e.g.
protons
,
deuterons
, …







2.


M
particle

=
M
electron



electrons

or

positrons




collisions

create

electron

ion

pairs


strongly

ionising

weakly

ionising

exponential

attenuation

with

depth

x

µ: material
dependent

attenuation

coefficient

%
3
1
R
R


Δ
for

all
elements

µx
e
)
x
(
N


no

defined

range

R!

Bragg
peak

well

defined

range

R!

Folie
19

CHARGED PARTICLES II: ENERY LOSS BY RADIATION

the

charge

polarizes

the

medium









emission

under

specific

angle

C


Radiation
if

v
particle

>
c
in

medium

Cerenkov 1930s


C

measures

the

velocity

of

the

particle


electrons

„
radiate
“

in
the

water

above


the

core

of


a
nuclear

power plant

cos

C
= 1 /

n

n =
index

of

refraction

(
small
)
dispersion

!

acoustics

analogue
: Mach‘s
cone

for

supersonic

source

„light“
blue
!

collision
x
E
radiation
C
x
E






<<






Δ
Δ
Δ
Δ
Folie
20

INTERACTION OF


MASSIVE NEUTRAL PARTICLES


WITH MATTER

Folie
21

n
eutrons

–

no

defined

range


detection

by

recoil

of

protons


(
from

hydrogen)


M
Proton



M
Neutron




i.e.
good

shieldings

are

water





concrete

(15%
water
)




paraffin

( (CH)
n
)




…

NEUTRONS

collisions

create

recoil

particles



maximum

energy

transfer

for

M
neutral

=
M
recoil



central

collision

all
energy

is

transferred

non
central


all
energies

according

to

scattering

angle


cloud

chamber

picture

neutrons

energy

transfer

D
䔠

p敲
捯llisin

D
䔠

pbability

Folie
22

INTERACTION OF


RADIATION WITH MATTER

Folie
23

RADIATION I : PHOTO
EFFECT

1.

photon

disappears


photo

electron

E
e

=
E
photon

-

E
B


2.

refilling

of

hole in
electron

shell

by


a)
emission

of

photon

or


b)
Auger

electron

emission

of




loosely

bound

outer

electron



E
Auger




B



detected

energy

E


photo

peak


E
=
E
photon






=
E
e

+
E
B


escape

peak


E =
E
photon

-

E
K
a

example


Argon

E
K
a

= 2.95
keV

photon

E
Photon

= 6.41
keV


photo


peak




escape


peak

requires

particle

nature

of

„light“
Einstein 1905

Energy

Folie
24

RADIATION II
:
COMPTON EFFECT


photon

does

not

disappear

recoil

electron


E
e

=
E
photon

–

E
photon
‘





†


捯c瑩t畯畳
†
獰散瑲畭



detected

energy



E
=
E
e


we

neglegt

E
B

of

the

electron

and

E
recoil

of

the

nucleus


because

usually

E
B
,
E
recoil

<<
E
e

proof

of

particle

nature

of

„light“

Compton 1922

billard

with

photons

and

„
quasifree
“
electrons

Δλ =λ (1−
cos
θ )

Compton
edge

=
maximum

energy

transfer

Folie
25

RADIATION III
:
BREMSSTRAHLUNG


bending

force

by

Coulomb potential

force




慣捥汥a慴楯n
†








any

distance

r


†

捯c瑩t畯畳
†
獰散瑲畭

accelerated

charged

particles

radiate

Hertz 1886

electromagnetic

waves

characteristic

X
-
rays

refilling

of

holes


in
inner

atomic

shells

a
recoil

partner

(
nucleus
)
is

needed

to

fulfil


energy

and

momentum

conservation


r
m
2
r
nucleus
Q
particle
Q
0
4
1
Coulomb
F







πε
Folie
26

RADIATION IV : PAIR
PRODUCTION

+Ze

E
p
hoton

= h
n

㸠㈠
m
electron

in general > 2
m
particles

at very high energies







el.
-
mag shower


e
+

e

–

g

-

casca摥

pair

production

and
Bremsstrahlung alternate

shower
may start with photon
or

electron


radiation length x
0


characteristic material dependent constant

depth, where about 2/3 of the incident energy is converted

proof

of

mass
-
energy

equivalence

Blackett 1948

conversion

of

energy

into

matter



magnetic

field

B

a
recoil

partner

(
nucleus
)
is

needed

to

fulfil


energy

and

momentum

conservation


Folie
27

CHARGED PARTICLES : SUMMARY I

Fractional energy
loss.

MIPs

minimum

ionsing

particles





ρ
Δ
Δ
1
x
E
dx
dE










2

M
0

...
v
1
x
E
2
collision







Δ
Δ
T < 2

M
0

stopping

power





Folie
28

CHARGED PARTICLES : SUMMARY II

Fractional energy loss per radiation length in lead as
a function
of electron or positron energy.

Folie
29

RADIATION: SUMMARY I



cross

section

s


Z
5


s


†
敡捴in

pbability

Folie
30

RADIATION: SUMMARY II

intensity

after
layer

thickness

x

attenuation

x
)
h
(
0
e
I
)
x
(
I
ν
μ


Lambert
-
Beer law

x
)
h
(
0
e
I
)
x
(
I
ν
μ


I
o

I

x

dx

transmission

)
h
(
)
h
(
i
i
ν
μ
ν
μ


sum

of

linear
attanuation

coeff
.

Folie
31

DETECTOR PRINCIPLES

Folie
32

(Wilson)
cloud

chamber

typical

Open Day
presentations


saturated

alcohol

vapor





a
-
particle

emitting

nuclide


overheated

LH
2


bubble

chamber

(D. Glaser noble
prize

1960)

+

magnetic

field


"
beer
"
inspired

!!!



among

others

discovery

of

the

weak

neutral
current


BEBC @ CERN 73 until 80ies

3.7 T, 35 m
3

LH
2


not only HISTORY

Folie
33

CHARGE

capacitor

voltage

generator

ionising

particle

current

or

voltage

detection

charge

created

by

charged

particles

or

by

„light“

is

collected


by

applying

a
voltage

by

means

of

a
curent

or

voltage

detection


Folie
34

SCINTILLATORS produce “LIGHT”

ionisation

caused

by


charged

particles

or

light

excitation

and

delayed

light
emission

usually

in
the

UV
range


anorganic


NaI
(
Tl
), CSI, BaF
2
, …

inorganic

doped

„
plastics
“




UV light
is

converted

to

charge

at

a
photo

cathode

and


multiplied

by

a
multi

stage

photo

„
multiplier
“



Folie
35

TIME

10
ns

Folie
36

WIRE CHAMBERS I

to control avalanche

quench gases, e.g. CO
2
, CH
4
, C
2
H
6

multiplication



avalanche

gain

10
5

-

10
6

wire

chambers

tutorial
:

F.
Sauli

CERN
yellow

report

99
-
07

electron

multiplication

around

anode

(fast)


drift

of

ions

(
slow
)

typical

ion

drift

velocity
:


1
-

10 cm/(µ
s

歖
)

䅲†⁃
4

Folie
37

WIRE CHAMBERS
II

many

wires
: MWPC =
multiwire

proportional
chamber


position

resolution


†
睩we

d楳瑡湣n

瑹t楣i汬l

2m

•
(
x,y
)
-

coordinate

per pair
of

frames


•
trajectory

from

MWPC
stacks

field

configuration

Folie
38

tracking
:
cut

on
fiducial

target

volume


example
:
p
-
3
He


灮p

or

dn

WIRE CHAMBERS
III

3
He
vesssel

pion

beam


beam
defining

counters

mainly

p

carbon

reactions

protons

deuterons

MWPC 1

MWPC 2

target

beam
defining


counters

good

bad

event

Folie
39

"simple" mechanics

10 MHz rate

inside magnetic field

ZEUS
-

DESY wedge

Type
-
2 module (520 ‘straws’)

ATLAS at the LHC

individual
counters
,
timing

20
ns

HV:
coat
,
ground
: sense
wire

(
~
kV
)

typical

size
:
length

1
-

2 m,
f
mm
-

cm

resistive read out

I
left

I
right

z

D
z < 1 mm

Monte Carlo

simulation

gas filling

e.g., Ar/C
2
H
6

wall: aluminised mylar foils

anode wire:
f



20 µm

STRAW TUBES

Folie
40

time


position

external time reference,

e.g.,
plastic scintillator

trick: choose field configuration,

which keeps the nonlinearity of

time
-
to
-
position relation small

position resolution

DRIFT CHAMBERS
I

20 µm

Folie
41

The wires are arranged in layers that
pass through the cylinder at three
different angles. The set of wires that
give a signal can be used to allow
computer reconstruction of the paths (or
tracks) of all the charged particles
through the chamber.

The "drift" in the name of this chamber refers to the time it takes electrons to drift to the
nearest sense wire from the place where the high
-
energy particle ionized an atom. Any three
sense wires are only nearby in one place so a set of "hits" on these three fix a particle track in
this region. By measuring the drift time, the location of the original track can be determined
much more precisely than the actual spacing between the wires.

improved position resolution by nearest 3 wires method

inclined wires

DRIFT CHAMBERS II

Folie
42

properties:

•
full 3
-
dimensional detector

•
constant drift velocity due to the collisions


in the gas mixture (typical a few cm/µs).

•
low occupancy even for high background (high rates)

•
large dE/dx due to large gas thickness (particle identification)

idea: avoid pile
-
up many MWPC planes (typical gas thickness of 1 cm)



principle: electrons produced follow the
constant

electric field lines to a single MPWC plane


located at one end of the volume ( x
-
y coordinates on this plane)


Third coordinate, z, from the drift time of the electrons to the anode plane

STAR TPC
-

RHIC, Brookhaven

TPC
-

time
projection

chamber

David
Nygren
, 1974


Folie
43

Single Track

Track Cluster

Pixel
Tracker


•

Pixel Size

•

Occupancy

•

Charge Sharing

•

S/N

•

ExB

Drift

•

Radiation
Damage



LHC
-

10
14

/cm
2
/
yr

v
ertex
r
esolution

(20
-
30
)
m
m
IP

& Trigger

Charge Sharing

charge center of gravity



high position resolution

Folie
44

+



+



charged

particle

principle



pn diode


as almost all

semiconductor detectors

miniaturisation

Readout Chip

Sensor

arrays of soldering dots

typical x
-
y (front
-
back)

arrangements


200 µm strips

layer thickness 300 µm

SILICON MICRO
-

STRIP DETECTORS I

Folie
45

CMS
-

LHC scheme

silicon µ
-
strip module

semiconductor telescope

65/300/300/5500 µm thick

double
-
sided Si
-
strip detectors

ANKE
-

COSY

•
inner tracker

•
vertex detection

•
recoils

•
polarisation (left
-
right asymmetry)

SILICON MICRO
-

STRIP DETECTORS

II

Folie
46

EXAMPLES


OF


COMBINED DETECTION SYSTEMS

Folie
47

focal

plane

particle identification by dE/dx

2
2
2
1
p
m
T
m
v
dx
dE



counter

number

1

16

FOCAL
PLANE SPECTROMETER

for

positively

charged

particles

ANKE@COSY I: SET
-
UP

aim
:
measure

simultanuously

positively

and

negatively

charged

particles


e.g.
, pp

†
灰K
+

K


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48

ANKE@COSY II: FOCAL PLANE DETECTOR

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49

WASA@COSY I: SET
-
UP

aim
:
measure

photons

from

neutral
particle

decay

in
coincidence

with

charged

particles


e.g.
,
dd


†
4
He
p
0

gg

photon

detector
:
calorimeter

charged

particle

detector
:
forward

hodoscope

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50

WASA@COSY II:
CALORIMETER

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51

WASA@COSY III: FORWARD HODOSCOPE

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52


•
Silicon Vertex
Tracker

(SVT)
-


precise

position

information

on
charged

tracks


•
Drift
Chamber

(DCH)
-

the

main

momentum

measurements

for

charged

particles

and

helps

in
particle

identification

through

dE
/dx
measurements

•
Detector

of

Internally

Refected

Cerenkov
radiation

(DIRC
or

DRC)
-

charged

hadron

identification

•
Electromagnetic

Calorimeter

(EMC)
-

particle

identification

for

electrons
,
neutral
electromagnetic

particles
,
and

hadrons

•
Solenoid (not a
subdetector
)
–

high
magnetic

field

for

needed

for

charge

and

momentum

measurements

•
Instrumented

Flux

Return (IFR)
-

muon

and

neutral
hadron

identification

•
and

more

…




Todays

detectors

comprise

...

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53

EXERCISES LECTURE 9: PARTICLE DETECTORS

1.
Derive

the

nonrelativistic

relation

between

kinetic

energy

and

momentum

from

the

relativistic

energy
-
momentum

relation
.

2.
By

which

process

charged

particles

loose

kinetic

energy

in matter?

3.
Which

process

dominates

–

depending

on
the

energy

of

the

radiation

–

the

attenuation

in matter?

4.
Which

processes

are

involved

in an X
-
ray

session

at

your

medical

doctor

having

an
apparatus

labeled

25
keV
?

5.
Which

is

the

minimum

velocity

(in
units

of

speed

of

light c)
for

particles

in
order

to

produce

Cerenkov light in
plastic

material
with

index

of

refraction

n = 1.5?

6.
Which

kind

of

detector

should

be

used

to

detect

neutral
pion

decays
?

7.
How

many

planes
of

MWPCs
are

needed

to

measure

the

trajectory

of

a
charged

particle

with

and

without

the

presence

of

a
magnetic

field

B.