close

Вход

Забыли?

вход по аккаунту

?

Particle Detectors

код для вставкиСкачать
Introduction
Summer Student Lecture Series 2003
Christian Joram
EP / TA1
From (very) basic ideas
to
rather complex
detector systems
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/1
Introduction
Outline + approximate timing
пѓњ
Introduction, basics
пѓњ
Tracking (gas, solid state)
пѓњ
Scintillation and light detection
пѓњ
Calorimetry
пѓњ
Particle Identification
пѓњ
Detector Systems
пѓњ
Discussion session I
Fri, 4 June, 11:15
пѓњ
Discussion session II
Tue, 8 June, 11:00
Thu/Fri
(2x45 min)
Mon/
Tue
(2 x45 min)
Wed
(45 min)
= Detector Exhibition
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/2
Introduction
Literature on particle detectors
пЃµ
Text books
пЃ®
C. Grupen, Particle Detectors, Cambridge
University Press, 1996
пЃ®
G. Knoll, Radiation Detection and Measurement,
3rd Edition, 2000
пЃ®
пЃ®
пЃ®
пЃ®
пЃµ
Review articles
пЃ®
пЃ®
пЃ®
пЃµ
W. R. Leo, Techniques for Nuclear and Particle
Physics Experiments, 2nd edition, Springer, 1994
R.S. Gilmore, Single particle detection and
measurement, Taylor&Francis, 1992
W. Blum, L. Rolandi, Particle Detection with Drift
Chambers, Springer, 1994
K. Kleinknecht, Detektoren fГјr Teilchenstrahlung,
3rd edition, Teubner, 1992
Experimental techniques in high energy physics, T.
Ferbel (editor), World Scientific, 1991.
Instrumentation in High Energy Physics, F. Sauli
(editor), World Scientific, 1992.
Many excellent articles can be found in Ann. Rev.
Nucl. Part. Sci.
Other sources
пЃ®
пЃ®
Particle Data Book (Phys. Rev. D, Vol. 54, 1996)
R. Bock, A. Vasilescu, Particle Data Briefbook
http://www.cern.ch/Physics/ParticleDetector/BriefBook/
пЃ®
Proceedings of detector conferences (Vienna VCI,
Elba, IEEE)
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/3
Introduction
“The oldest particle detector”
(built many billion times)
• High sensitivity to photons
• Good spatial resolution
• Very large dynamic range (1:1014)
+ automatic threshold adaptation
• Energy (wavelength) discrimination
• Modest speed.
Data taking rate ~ 10Hz (incl. processing)
retina
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/4
Introduction
Use of photographic paper as detector
пѓ Detection of photons / x-rays
W. C. Röntgen, 1895
Discovery of the �X-Strahlen’
Photographic paper/film
e.g. AgBr / AgCl
AgBr + �energy’
пѓ metallic Ag (blackening)
+ Very good spatial resolution
+ Good dynamic range
- No online recording
- No time resolution
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/5
Introduction
J. PlГјcker 1858 пѓ J.J. Thomson 1897
Thomson’s cathode ray tube
accelerator
manipulation
By E or B field
detector
From: J.J. Thomson: Cathode Rays.
Philosophical Magazine, 44, 293 (1897).
“… The rays from the cathode C pass through a slit in the anode
A, which is a metal plug fitting tightly into the tube and connected
with the earth; after passing through a second slit in another earthconnected metal plug B, they travel between two parallel
aluminium plates about 5 cm. long by 2 broad and at a distance of
1.5 cm. apart; they then fall on the end of the tube and produce a
narrow well-defined phosphorescent patch. A scale pasted on the
outside of the tube serves to measure the deflexion of this
patch….”
Scintillation of glass
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/6
Introduction
E. Rutherford
1909
H. Geiger
pulse
The Geiger counter, later further developed and then called
Geiger-MГјller counter
First electrical signal from a particle
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/7
Introduction
C. T. R. Wilson,
1912, Cloud chamber
First tracking
detector
The general procedure was to allow water to evaporate in an enclosed
container to the point of saturation and then lower the pressure, producing a
super-saturated volume of air. Then the passage of a charged particle would
condense the vapor into tiny droplets, producing a visible trail marking the
particle's path.
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/8
Introduction
“progress cycle”
physics
theories
technologies
& materials
knowledge /
progress
experiments
CERN Summer Student Lectures 2003
Particle Detectors
detectors
Christian Joram
I/9
Introduction
A W+W- decay in ALEPH
e+e- (пѓ–s=181 GeV)
п‚® W+W- п‚® qqmnm
п‚® 2 hadronic jets
+ m + missing momentum
CERN Summer Student Lectures 2003
Particle Detectors
_
Christian Joram
I/10
Introduction
Reconstructed B-mesons in the DELPHI
micro vertex detector
tB п‚» 1.6 ps l = ctg п‚» 500 mmпѓ—g
Primary
Vertex
Primary
Vertex
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/11
Introduction
A simulated event in ATLAS (CMS)
H п‚® ZZ п‚® 4m
pp collision at пѓ–s = 14 TeV
L = 1034 cm-2 s-1, bunch
sinel. п‚» 70 mb
spacing 25 ns
m
Interested in processes
with s п‚» 10-100 fb
m
m
m
п‚» 23 overlapping minimum bias events / BC
п‚» 1900 charged + 1600 neutral particles / BC
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/12
Introduction
Idealistic views of an elementary particle reaction
+
-
e + e п‚® Z п‚® qq
0
( + hadronizat
e+
q
Z
q
time
e-
ion)
• Usually we can only �see’ the end products of
the reaction, but not the reaction itself.
• In order to reconstruct the reaction mechanism
and the properties of the involved particles, we
want the maximum information about the end
products !
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/13
m
Introduction
The �ideal’ particle detector should provide…
detector
+
-
e e , ep,
end products
• charged
• neutral
• photons
pp, p p
пЃµ
coverage of full solid angle (no cracks, fine
segmentation
measurement of momentum and/or energy
detect, track and identify all particles (mass,
charge)
fast response, no dead time
пЃ‡
practical limitations (technology, space, budget)
пЃµ
пЃµ
пЃµ
Particles are detected via their interaction
with matter.
Many different physical principles are involved
(mainly of electromagnetic nature).
Finally we will always observe...
ionization and excitation of matter.
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/14
m
Definitions and units
Some important definitions and units
пЃІ2 2
2
2 4
E пЂЅ p c + m0 c
п‚џ
п‚џ
п‚џ
energy E:
momentum p:
mass mo:
пЃў пЂЅ
v
measure in eV
measure in eV/c
measure in eV/c2
пЂЁ0 п‚Ј пЃў
c
E пЂЅ m 0g c
2
пЂј 1пЂ©
g пЂЅ
p пЂЅ m 0 gпЃў c
1
1- пЃў
пЂЁ1 п‚Ј g
2
пЃў пЂЅ
пЂј п‚ҐпЂ©
pc
E
1 eV is a tiny portion of energy. 1 eV = 1.6В·10-19 J
mbee = 1g = 5.8В·1032 eV/c2
vbee= 1m/s п‚® Ebee = 10-3 J = 6.25В·1015 eV
ELHC = 14В·1012 eV
To rehabilitate LHC…
Total stored beam energy:
1014 protons * 14В·1012 eV п‚» 1В·108 J
mtruck = 100 T
vtruck = 120 km/h
this corresponds to a
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/15
Definitions and units
The concept of cross sections
Cross sections s or differential cross sections ds/dW are
used to express the probability of interactions between
elementary particles.
Example: 2 colliding particle beams
F1 = N1/t
beam spot area A
F2 = N2/t
What is the interaction rate Rint. ?
Rint п‚µ N1N2 / пЂЁA В· t) = s В·
L
Luminosity L [cm-2 s-1]
s has dimension area !
Practical unit:
1 barn (b) = 10-24 cm2
Example: Scattering from target
target
scattered
beam
solid angle
element dW
q
incident
beam
.nA =
area density
of scattering
centers in target
CERN Summer Student Lectures 2003
Particle Detectors
Nscat(q) п‚µ NincВ· nA В· dW
= ds/dW (q) В· NincВ·nAВ· dW
Christian Joram
I/16
Momentum measurement
Multiple scattering
Bethe-Bloch formula
/ Landau tails
Ionization of gases
Wire chambers
Drift and diffusion in gases
Drift chambers
Micro gas detectors
Silicon as a detection medium
Silicon detectors strips/pixels
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/17
Momentum measurement
пЃ‚
пЃ‚
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/18
Momentum measurement
Momentum measurement
mv
L
пЃІ
2
пЂЅ q (v п‚ґ B )
p T пЂЅ qB пЃІ
п‚®
x
B
s
p T ( GeV c ) пЂЅ 0 . 3 B пЃІ
y
L
2пЃІ
пЂЅ sin q 2 п‚» q 2
(T пѓ— m)
q п‚»
п‚®
0 .3 L пѓ— B
pT
пЃІ
s пЂЅ пЃІ пЂЁ1 - cos q 2 пЂ© п‚» пЃІ
q
q
2
8
2
п‚»
0 .3 L B
8
pT
the sagitta s is determined by 3 measurements with
error s(x):
s пЂЅ x 2 - 12 ( x1 + x 3 )
s пЂЁ pT
пЂ©
meas .
пЂЅ
pT
s (s)
3
s
2
пЂЅ
s
(x)
пЂЅ
s
3
s
2
( x ) пѓ— 8 pT
0 . 3 пѓ— BL
2
for N equidistant measurements, one obtains
(R.L. Gluckstern, NIM 24 (1963) 381)
s пЂЁ pT
пЂ©
meas .
пЂЅ
pT
s ( x ) пѓ— pT
0 . 3 пѓ— BL
2
720 /( N + 4 )
(for N п‚і п‚»10)
ex: pT=1 GeV/c, L=1m, B=1T, s(x)=200mm, N=10
s пЂЁ pT
пЂ©
meas .
п‚» 0 .5 %
pT
CERN Summer Student Lectures 2003
Particle Detectors
(s п‚» 3.75 cm)
Christian Joram
I/19
Multiple Scattering
Scattering
An incoming particle with charge z interacts with
a target of nuclear charge Z. The cross-section
for this e.m. process is
2
ds
1
2пѓ¦ m c пѓ¶
пЂЅ 4 zZr e пѓ§пѓ§ e пѓ·пѓ·
4
dW
пѓЁ пЃў p пѓё sin q 2
Rutherford formula
d s /d W
scattering angle q пЂЅ 0
пЃµ Cross-section for q п‚® 0 infnite !
пЃµ Average
q
Multiple Scattering
Sufficiently thick material layer
п‚® the particle will undergo multiple scattering.
L
sian
Gaus
P
r p la ne
sin -4(q
/2)
q p la ne
q0
0
q 0 пЂЅ q plane пЂЅ
RMS
CERN Summer Student Lectures 2003
Particle Detectors
q plane
2
пЂЅ
Christian Joram
1
2
q
qplane
RMS
space
I/20
Momentum measurement
q0 п‚µ
Approximation
1
L
p
X0
X0 is radiation length of the medium (discuss later)
Back to momentum measurements:
What is the contribution of multiple scattering to
remember
s ( p)
pT
?
п‚µ s ( x ) пѓ— pT
pT
s ( x)
s ( p)
s ( p)
MS
More precisely:
п‚µ q0 п‚µ
s ( p)
1
MS
пЂЅ constant
pT
independent
of p !
p
MS
1
пЂЅ 0 . 045
pT
B
LX
0
s (p )/p
tota l e rror
s (p )/p
m ea s.
s (p )/p
MS
p
• ex: Ar (X0=110m), L=1m, B=1T
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
s ( p)
MS
п‚» 0 .5 %
pT
I/21
Interaction of charged particles
Detection of charged particles
How do they loose energy in matter ?
пЃµ
Discrete collisions with the atomic electrons of the
absorber material.
пЃІ
v , m0
q
dE
пЃЁпЃ· , пЃЁk
dx
e-
п‚Ґ
пЂЅ - пѓІ NE
0
N : electron
ds
пЃЁ dпЃ·
dE
density
Collisions with nuclei not important (me<<mN).
пЃµ
If
пЃЁпЃ· , пЃЁk
are big enough пѓ° ionization.
Instead of ionizing an atom, under certain conditions the
photon can also escape from the medium.
пѓ°
Emission of Cherenkov and Transition
radiation. (See later).
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/22
Bethe-Bloch formula
Average differential energy loss dE
dx
Ionisation only п‚® Bethe - Bloch formula
dE
пЂЅ - 4пЃ° N
dx
2
2 2
A re m e c z
2 2
Z 1 пѓ© 1 2mec g пЃў
ln
2 пѓЄ2
2
A пЃў пѓ«
I
пЃ¤пѓ№
2
T
max
-пЃў
2
-
пѓє
2пѓ»
пЃµ
dE/dx in [MeV g-1 cm2]
пЃµ
Bethe-Bloch formula only valid for “heavy” particles (mmm).
пЃµ
dE/dx depends only on пЃў, independent of m !
пЃµ
First approximation: medium simply characterized by
Z
A
~ electron density
Z/A = 1
“Fermi plateau”
Z/A~0.5
dE dx п‚» 1..2 MeV g
-1
cm
2
dE
п‚µ ln пЃў g
2
2
dx
dE
dx
п‚µ
“relativistic rise”
1
пЃў
2
“kinematical term”
CERN Summer Student Lectures 2003
Particle Detectors
пЃўg п‚» 3-4
minimum ionizing particles, MIPs
Christian Joram
I/23
Landau tails
Real detectors (limited granularity) can not measure
<dE/dx> !
It measures the energy DE deposited in a layer of
finite thickness пЃ¤x.
For thin layers (and low density materials):
п‚® Few collisions, some with high energy transfer.
e-
<DE>
п‚® Energy loss distributions show large
fluctuations towards high losses:
”Landau tails”
DE
For thick layers and high density materials:
п‚® Many collisions.
п‚® Central Limit Theorem п‚® Gaussian shape distributions.
e-
<DE>
DE
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/24
Ionization of gases
Gas detectors
Fast charged particles ionize the atoms of a gas.
Primary ionization
Total ionization
10 - 40 pairs/cm
DE/pair ~ 20 - 40 eV
n total п‚» 3пЃ‹ 4 пѓ— n primary
Often the resulting primary electron will have enough
kinetic energy to ionize other atoms.
• Assume detector, 1 cm thick, filled with Ar gas:
1 cm
~ 100 e-ion pair
п‚» 100 electron-ion pairs are not easy to detect!
Noise of amplifier п‚»1000 e- (ENC) !
We need to increase the number of e-ion pairs.
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/25
Proportional Counter
Gas amplification
Consider cylindrical field geometry (simplest case):
E
ca tho d e
g as
E th resh o ld
b
a
1 /r
a no de
E пЂЁr пЂ© пЂЅ
V (r ) пЂЅ
CV 0
пѓ—
a
1
r
2пЃ°пЃҐ 0 r
CV 0
2пЃ°пЃҐ 0
пѓ— ln
r
a
C = capacitance / unit length
Electrons drift towards the anode wire (п‚» stop and go! More
details in next lecture!).
Close to the anode wire the field is sufficiently high (some
kV/cm), so that e- gain enough energy for further ionization п‚®
exponential increase of number of e--ion pairs.
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/26
Proportional Counter
n пЂЅ n0 e
пЃЎ пЂЅ
1
пЃ¬
пЃЎ пЂЁE пЂ©x
or n пЂЅ n 0 e
пЃЎ: First Townsend coefficient
(e--ion pairs/cm)
пЃЎ пЂЁr пЂ©x
пЃ¬: mean free path
пѓ© rC
пѓ№
M пЂЅ
пЂЅ exp пѓЄ пѓІ пЃЎ пЂЁ r пЂ©dr пѓє
n0
пѓЄпѓ« a
пѓєпѓ»
n
Gain
M п‚» ke
CV 0
(F. Sauli, CERN 77-09)
пЃҐ
CERN Summer Student Lectures 2003
Particle Detectors
(O. Allkofer, Spark chambers,
Theimig MГјnchen, 1969)
Christian Joram
I/27
Proportional Counter
Signal
formation
(F. Sauli, CERN 77-09)
Avalanche formation within a few wire radii and within
t < 1 ns!
Signal induction both on anode and cathode due to
moving charges (both electrons and ions).
dv пЂЅ
Q
dV
dr
lCV 0 dr
Electrons collected by anode wire, i.e. dr is
small (few mm). Electrons contribute only very
little to detected signal (few %).
Ions have to drift
back to cathode,
i.e. dr is big.
Signal duration
limited by total ion
drift time !
(F. Sauli, CERN 77-09)
Need electronic signal differentiation to limit dead time.
CERN Summer Student Lectures 2003
Particle Detectors
Christian Joram
I/28
Документ
Категория
Презентации
Просмотров
29
Размер файла
954 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа