Mitglied der Helmholtz-Gemeinschaft Lecture 9 PARTICLE
DETECTORS Detlev Gotta Institut fr Kernphysik, Forschungszentrum
Jlich / Universitt zu Kln GGSWBS'12, Batumi, Georgia 5th Georgian
German School and Workshop in Basic Science August 16, 2012
Slide 2
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 ?
Slide 3
Folie 3 WHAT TO DETECT ?
Slide 4
Folie 4 PARTICLES Light Heavy particle
detectorregistration
Slide 5
Folie 5 PARTICLES What characterizes a particle? mass M charge
Q Spin intrinsic angular momentumS life time shape (for extended
particles)
Slide 6
Folie 6 RADIATION fluid gas light fundamental constant: c =
speed of light in vacuum ( 30 cm / ns)
Slide 7
Folie 7 RADIATION What characterizes waves? wave propagation
velocityc = wave length frequency particle physics usually
electromagnetic radiation wave propagation velocity in vacuum c =
in medium c = c index of refaction n = c / c
Slide 8
Folie 8 CONSTITUENTS OF MATTER I atoms 10 -10 m atomic shells
nucleus electron proton neutron e p n Q 1 + 1 0 M M p / 1836 M p M
p size < 10 -18 m 0.8 10 -15 m life time 0 > 10 26 y > 10
29 y 886 s decay - - n p e
Slide 9
Folie 9 CONSTITUENTS OF MATTER II pions kaons many more K Q 0,
1 2 0, 1 M M p / 7 M p / 2 size 0.6 10 -15 m 0.6 10 -15 m life time
0 26 10 -9 s K 12 10 -9 s 0 8 10 -17 s K 0 S,L 9 10 -10 / 5 10 -8 s
decay new particles unstable being free
Slide 10
Folie 10 PARAMETERS total energy rest massm 0 0 range in matter
= 0 attenuation in matter chargeQ 0 deflection in el.-mag fields =
0 no deflection life time = 0 decay length l = v = relativistic
factor massive particles el.-mag. radiation h Planck constant =
minimal action
Slide 11
Folie 11 HOW TO DETECT ?
Slide 12
Folie 12 FORCES nuclear forcekeeps protons and neutrons
together electromagnetic forcekeeps electrons around the nuclei
weak force makes the (free) neutron to decay gravitationkeeps us on
the ground strength Standard Model
Slide 13
Folie 13 ELECTROMAGNETIC FORCE a force is mediated classical
picture quantum world by field around a source field quanta =
particles light particles = photons electromagnetic radiation = E
and B fields interacts with electric charges
Slide 14
Folie 14 DEFLECTION OF CHARGED PARTICLES IN EL.-MAG. FIELDS
electric field magnetic field B = const. circular motion B plane of
projection r
Slide 15
Folie 15 SIGNAL CREATION via electric charges measure the
electric current I or voltage U resistor R U I capacitor C U Q
Slide 16
Folie 16 INTERACTION OF CHARGED PARTICLES WITH MATTER
Slide 17
Folie 17 beforeafter 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
Slide 18
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 : material dependent attenuation coefficient for all
elements no defined range R! Bragg peak well defined range R!
Slide 19
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 ! Cerenkov wave front acoustics
analogue: Machs cone for supersonic source light blue!
Slide 20
Folie 20 INTERACTION OF MASSIVE NEUTRAL PARTICLES WITH
MATTER
Slide 21
Folie 21 neutrons 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 collisionall energy is transferred non centralall
energies according to scattering angle cloud chamber picture
neutrons energy transfer E per collision EE probability
Slide 22
Folie 22 INTERACTION OF RADIATION WITH MATTER
Slide 23
Folie 23 RADIATION I : PHOTO EFFECT 1.photon disappears photo
electronE 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 E B detected energy E photo peak E = E
photon = E e + E B escape peak E = E photon - E K example Argon E K
= 2.95 keV photonE Photon = 6.41 keV photo peak escape peak
requires particle nature of light Einstein 1905 Energy
Slide 24
Folie 24 RADIATION II : COMPTON EFFECT photon does not
disappear recoil electronE e = E photon E photon continuous
spectrum detected energy E = E e we neglegt E B of the electron and
E recoil of the nucleus because usually E B, E recoil
Folie 26 RADIATION IV : PAIR PRODUCTION +Ze E photon = h > 2
m electron in general > 2 m particles at very high energies
el.-mag shower e + e - cascade 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
Slide 27
Folie 27 CHARGED PARTICLES : SUMMARY I Fractional energy loss.
MIPs minimum ionsing particles 2 M 0 T < 2 M 0 stopping
power
Slide 28
Folie 28 CHARGED PARTICLES : SUMMARY II Fractional energy loss
per radiation length in lead as a function of electron or positron
energy.
Slide 29
Folie 29 RADIATION: SUMMARY I cross section reaction
probability
Slide 30
Folie 30 RADIATION: SUMMARY II intensity after layer thickness
x attenuation Lambert-Beer law IoIo I x dx transmission sum of
linear attanuation coeff.
Slide 31
Folie 31 DETECTOR PRINCIPLES
Slide 32
Folie 32 (Wilson) cloud chamber typical Open Day presentations
saturated alcohol vapor -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
Slide 33
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
Slide 34
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
Slide 35
Folie 35 TIME 10 ns
Slide 36
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/(s kV) Ar CH 4
Slide 37
Folie 37 WIRE CHAMBERS II many wires: MWPC = multiwire
proportional chamber position resolution wire distance typically 2
mm (x,y) - coordinate per pair of frames trajectory from MWPC
stacks field configuration
Slide 38
Folie 38 tracking: cut on fiducial target volume example: -3 He
pnn or dn WIRE CHAMBERS III 3 He vesssel pion beam beam defining
counters mainly carbon reactions protons deuterons MWPC 1 MWPC 2
target beam defining counters good bad event
Slide 39
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, mm - cm resistive read out I left
I right z z < 1 mm Monte Carlo simulation gas filling e.g., Ar/C
2 H 6 wall: aluminised mylar foils anode wire: 20 m STRAW
TUBES
Slide 40
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 m
Slide 41
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
Slide 42
Folie 42 properties: full 3-dimensional detector constant drift
velocity due to the collisions in the gas mixture (typical a few
cm/s). 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
Slide 43
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 vertex resolution (20-30) m IP & Trigger Charge
Sharing charge center of gravity high position resolution
Slide 44
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 m
strips layer thickness 300 m SILICON MICRO - STRIP DETECTORS I
Folie 47 focal plane particle identification by dE/dx 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 pp K + K
Slide 48
Folie 48 ANKE@COSY II: FOCAL PLANE DETECTOR
Slide 49
Folie 49 WASA@COSY I: SET-UP aim: measure photons from neutral
particle decay in coincidence with charged particles e.g., dd 4 He
0 photon detector: calorimetercharged particle detector: forward
hodoscope
Slide 50
Folie 50 WASA@COSY II: CALORIMETER
Slide 51
Folie 51 WASA@COSY III: FORWARD HODOSCOPE
Slide 52
Folie 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...
Slide 53
Folie 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.