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
Saturday Physics, 12/4/99
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 !
Saturday Physics, 12/4/99
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
+-
Saturday Physics, 12/4/99
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
+++
++++++
++++++
++
+
Saturday Physics, 12/4/99
Linear AcceleratorLinear Accelerator
+ |
ENERGIZER
+
+ |
ENERGIZER
+
+ |
ENERGIZER
+
+ |
ENERGIZER+
+ |
ENERGIZER
+
Saturday Physics, 12/4/99
Linear AcceleratorLinear Accelerator
EN
ER
GIZ
ER
+
-
+
+
-+
-
Saturday Physics, 12/4/99
Linear AcceleratorLinear Accelerator
EN
ER
GIZ
ER
+
-
+
-
+
-+
Saturday Physics, 12/4/99
Linear AcceleratorLinear Accelerator
EN
ER
GIZ
ER
+
-
++
-+
-
Saturday Physics, 12/4/99
Linear AcceleratorLinear Accelerator
EN
ER
GIZ
ER
+
-
+
-
+
-+
Saturday Physics, 12/4/99
Linear AcceleratorLinear Accelerator
EN
ER
GIZ
ER
+
-+
+
-+
-
Saturday Physics, 12/4/99
Linear AcceleratorLinear Accelerator
+
-
+
+
-+
-
RF
Saturday Physics, 12/4/99
Some ExamplesSome Examples
LINAC at Fermilab(0.4 GeV)
LINAC at Bates Lab (MIT)(0.5 GeV)
Saturday Physics, 12/4/99
A Bigger ExampleA Bigger Example
SLAC (Stanford)(50 GeV)
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
Vacuum tube (beam pipe)
SynchrotronsSynchrotrons
bending magnet
Accelerating section
Focussingmagnets
Saturday Physics, 12/4/99
Booster (8 GeV)
Main Ring (150 GeV)
Tevatron (1000 GeV)
FermilabFermilab
Saturday Physics, 12/4/99
A slick trick A slick trick Two for the price of oneTwo for the price of one
1000 GeV-1000 GeV +
2000 GeV
Saturday Physics, 12/4/99
CERNCERN
LEP 200 GeV e+ e-
NOW
LHC 14000 GeV p p
In 5-6 years
Saturday Physics, 12/4/99
LEP TunnelLEP Tunnel
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
Most Common ApproachMost Common Approach(for colliding beam experiments)(for colliding beam experiments)
Detector “package” looks like a beer can
-+
Saturday Physics, 12/4/99
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.
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
Lets Try ItLets Try It
We don’t have an accelerator handy so lets look at cosmic rays:
p
Cloud chamber
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
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.
Saturday Physics, 12/4/99
The Periodic TableThe Periodic Table
Saturday Physics, 12/4/99
The Periodic Table Explained ?The Periodic Table Explained ?
proton
neutron
electron
Look carefully
Saturday Physics, 12/4/99
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 !
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
Mass from EnergyMass from Energy
KE1 KE2
Saturday Physics, 12/4/99
Mass from EnergyMass from Energy
Ebefore = Eafter
Mostly KE New Mass + KE
Saturday Physics, 12/4/99
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)
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
quarks & leptonsquarks & leptons
quark charge
up
down
charm
strange
top
bottom
+ 2/3
- 1/3
-1
0
e
e
lepton charge
Saturday Physics, 12/4/99
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
Saturday Physics, 12/4/99
Example: CLEOExample: CLEO
Saturday Physics, 12/4/99
Example: L3Example: L3
= 2 X
Saturday Physics, 12/4/99
Vertex Detector (CLEO)Vertex Detector (CLEO)
Saturday Physics, 12/4/99
Drift ChamberDrift Chamber
Saturday Physics, 12/4/99
CalorimeterCalorimeter
Saturday Physics, 12/4/99
SolenoidSolenoid