Atom Smashers Particle Accelerators and Detectors Mats Selen, UIUC

Saturday Physics, 12/4/99

Atom SmashersAtom SmashersParticle Accelerators Particle Accelerators

and Detectorsand Detectors

Mats Selen, UIUC

What’s the motivation ?

How to build a particle accelerator.

How to build a particle detector.

A great web site with lots of links is:

http://pdg.lbl.gov/particleadventure/english/index.html


What’s the Motivation ?What’s the Motivation ?

Try to make sense of the way the Universe worksLook for simple explanations to complicated looking observations !

ComplicationThere is lots of different “stuff” on earth

Simplification

Small indivisible “Atoms”There are many different kinds of atoms

Elements (Periodic Table)There are lots of elements

Nucleus (protons, neutrons) and electrons

We can make “other” stuff (not made of protons neutrons and electrons)

Everything madeout of quarks & leptons

We don’t really understand this at afundamental level (Standard Model has

too many free parameters) Smash More Atoms !


How to build a Particle AcceleratorHow to build a Particle Accelerator

First get some particles:

Electrons are easy: Just heat up a filament ee

eeeee

eeee

eeeee

Protons are also quite easy: Ionize hydrogen

+

e +

e

+

e

+

e

+e+

e

+

e

+

e

ENERGIZER

-+

ENERGIZER

+-


Now Accelerate ThemNow Accelerate Them

+ |

ENERGIZER

10,000,000,000 voltbattery

+

We’d like to give them lots of kinetic energy (lets say 10 GeV)

This can’t provide enough energy(only a few million volts) !

Need bigger voltage (and a vacuum system) !!

Do VdG & bubble demo

VanDeGraaff Accelerator

+++

++++++

++++++

++

+



EN

ER

GIZ

ER

+

-

+

+

-+

-



EN

ER

GIZ

ER

+

-

+

-

+

-+



EN

ER

GIZ

ER

+

-

++

-+

-



EN

ER

GIZ

ER

+

-

+

-

+

-+



EN

ER

GIZ

ER

+

-+

+

-+

-



+

-

+

+

-+

-

RF


Some ExamplesSome Examples

LINAC at Fermilab(0.4 GeV)

LINAC at Bates Lab (MIT)(0.5 GeV)


A Bigger ExampleA Bigger Example

SLAC (Stanford)(50 GeV)


But some people like to recycle...But some people like to recycle...

Have the particles go through the same accelerator cavitymany times

+

Circular “track”(high-vacuum beam-pipe)

This is called aSynchrotron

Need to make particles go in a circle

Key ingredients:

Need to keep everything synchronized

Small linear accelerator


Forces on Charged ParticlesForces on Charged Particles

Both electric and magnetic fields influence the motion of charges.

+ |

+ E

F = qEF

q

ENERGIZER

XXX X X X

XX X X X

XX X X X

X X X X

X X X XX

X

X X X

X X XX

Magnetic field “north” points into screen

F+

q v

+

q

Fv

F = qv x BE/m demoTV demoGeiger demo

ENERGIZER


Vacuum tube (beam pipe)

SynchrotronsSynchrotrons

bending magnet

Accelerating section

Focussingmagnets


Booster (8 GeV)

Main Ring (150 GeV)

Tevatron (1000 GeV)

FermilabFermilab


A slick trick A slick trick Two for the price of oneTwo for the price of one

1000 GeV-1000 GeV +

2000 GeV


CERNCERN

LEP 200 GeV e+ e-

NOW

LHC 14000 GeV p p

In 5-6 years


LEP TunnelLEP Tunnel


How to build a Particle DetectorHow to build a Particle Detector

Ideally, we want to measure everything (E, Px, Py, Px) about every particleproduced in the “collision”.

+ -

Charged Particles

Neutral Particles


Most Common ApproachMost Common Approach(for colliding beam experiments)(for colliding beam experiments)

Detector “package” looks like a beer can

-+


The PartsThe Parts

Solenoid (Magnet)

(Makes charged particles curve,which tells us their momentum)

Calorimeter to measure theenergy of neutral particles.

High density…particles often stop here.

Vertex Detector to measure theposition of charged particles close totheir point of creation.

Drift Chamber to measure the path of charged charged particles.

Low density…mostly gas…so particles don’t notice it much.


How it worksHow it works

All of the parts work more or less the same way:

Charged particles ionize the material they pass through, and we can detect signs of this ionization.

+e-

e-

detect electron+ e-

+

1)

Geiger counter


How it worksHow it works

All of the parts work more or less the same way:

Charged particles ionize the material they pass through, and we can detect signs of this ionization.

+e-

+ e-

+detect photon

2) + e-

scintillation

Scintillator counter


Lets Try ItLets Try It

We don’t have an accelerator handy so lets look at cosmic rays:

p

Cloud chamber


Scintillation DetectorScintillation Detector

Photons are produced in the plastic by scintillating molecules when a cosmic ray muon whizzes through it. These photons are detected by a photo-multiplier tube, and result in pulses on the oscilloscope.

Wrapped scintillator

Photo-multiplier

oscilloscope

Singlescoincidencebeta


Concluding RemarksConcluding Remarks

The pursuit of High Energy Physics is motivated by a quest for fundamental understanding.

Current accelerator and detector technology is very cool.


The Periodic TableThe Periodic Table


The Periodic Table Explained ?The Periodic Table Explained ?

proton

neutron

electron

Look carefully


The nucleus is much smaller than the atom

This is about 500 times too big

Even so, the nucleus contains > 99.9 % of the mass of the atom !


Energy vs MassEnergy vs Mass

He (m=4.0026 u) O (M=15.9995 u)

4 x He = 16.01 u

Mass difference = 0.01 u = binding energy

So energy is the same as mass somehow ??

E = mc2sure

Units


Mass from EnergyMass from Energy

KE1 KE2


Mass from EnergyMass from Energy

Ebefore = Eafter

Mostly KE New Mass + KE


UnitsUnits

E = mc2 E = m

Physicists are sloppy

Preferred unit of Energy/Mass = GeV

1eV = kinetic energy of an electron acceleratedthrough a 1 volt potential difference

+

-e-

EN

ER

GIZ

ER

1 voltbattery

This is a small amount of energy (more appropriate for chemistry)

1GeV = 109 eV (a billion eV)

(about the mass of a proton…appropriate scale for us)


It gets more complicated again...It gets more complicated again...

’

a0

f0

a1

h0

h1

f’2

f1

a2

f2

fj

a4

f4

K*

K

K1

K2

K*2

K3

K*3

K*4

Ds

D1

D*2

D*

D

D2

B*

B

Bs

Bc

c

c


quarks & leptonsquarks & leptons

quark charge

up

down

charm

strange

top

bottom

+ 2/3

- 1/3

-1

0

e

e

lepton charge


quarks & anti-quarksquarks & anti-quarks

proton neutron

+ D0 Bs

u

d

c

s

t

b

+ 2/3

- 1/3

- 2/3

+ 1/3

u

d

c

s

t

b

Now we can easily build any ofof the particles we have discovered(and predict some we haven't)

(baryons)

(mesons)

anti-proton


Example: CLEOExample: CLEO


Example: L3Example: L3

= 2 X


Vertex Detector (CLEO)Vertex Detector (CLEO)


Drift ChamberDrift Chamber


CalorimeterCalorimeter


SolenoidSolenoid

Atom Smashers Particle Accelerators and Detectors Mats Selen, UIUC

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