Particle Detectors

How to See the Invisible

2

How are Subatomic Particles Seen?

3

How are Subatomic Particles Seen?

By their interactions with ordinary matter.

Ionization of atoms or lattice Interaction with nucleus

Pair production

Bremstrahlung

Transition radiation

Cherenkov radiationScintillation

Synchrotron radiation

4

Which Subatomic Particles are Seen?

Which particles live long enough to bevisible in a detector?

5

Which Subatomic Particles are Seen?

Which particles live long enough to bevisible in a detector?

Protons

electrons

photons

neutrons

6

Which Subatomic Particles are Seen?

Which particles live long enough to bevisible in a detector?

Protons

electrons

photonsAnti-protons

positrons

muons and anti-muons

charged pions

neutrons anti-neutrons

neutral kaonscharged kaons

A few special cases of strange baryons.

A General Purpose Detector

8

Energy Loss

Muon momentum

1

10

100

Sto

ppin

g po

wer

[M

eV c

m2 /

g]

Lin

dhar

d-Sch

arff

Bethe-Bloch Radiative

Radiativeeffects

reach 1%

µ+ on Cu

Without !

Radiativelosses

"#0.001 0.01 0.1 1 10 100 1000 104 105 106

[MeV/c] [GeV/c]

1001010.1 100101 100101

[TeV/c]

Anderson-Ziegler

Nuclearlosses

Minimumionization

Eµc

µ$

Dependence on Material

1

2

3

4

5

6

8

10

1.0 10 100 1000 10 0000.1

Pion momentum (GeV/c)

Proton momentum (GeV/c)

1.0 10 100 10000.1

1.0 10 100 10000.1

1.0 10 100 1000 10 0000.1

!dE/d

x (M

eV g!1cm

2 )

"# = p/Mc

Muon momentum (GeV/c)

H2 liquid

He gas

CAl

FeSn

Pb

Energy loss depends on the type of material and particle.

Atoms with more higher Z have less energy loss per g/cm2

But their higher density (g/cm3) more than makes up for this.

Cerenkov Radiation

Emitted when a particle exceeds the speed of light in a medium

Like the shock wave from a supersonic plane

Cone angle is related to particle velocity

Scintillation

Many materials emit light when atoms or molecules are excited by a charged particle passing nearby

Emitted light is called scintillation

Scintillating medium usually transparent

Light (single or few photons) detected by a photomultiplier

12

The Fundamental Particles

The particle physicist’s periodic table consists of:

3 generations of quarks3 generations of leptons4 force carriers

The quarks and leptons are fermions, the force carriers are bosons.

How Do We Study Particles?Experiment:

Collide ParticlesAt very high energies

and convert energy intomass (i.e. other particles)

Where Are Particle Colliders?

FermiLab (Batavia, IL) CERN (Geneva Switzerland)

Some Examples:proton and neutron composed of up (u) and down (d) quarksproton is only stable hadron (baryon or mesonanti-proton and anti-neutron composed of anti-up and anti-down quarkspions are mesons composed of u and d quarksheavier baryons and mesons exist containing s, c, and b quarks (all are unstable)top decays before it can form bound states (earlier cartoon)

What About the Higgs?