Jefferson Lab
Presentation to Teacher Education Program
November 8, 2006
Subatomic Particles:
What do we study at Jefferson Lab?
Dr. Allison Lung
12 GeV Upgrade Project Director
&
Senior Staff Physicist
Nuclear Physics: All About Atoms
nucleons
education.jlab.org/atomtour
Building atoms……
The tiniest particles……or are they?
Just how big are they?
What about all that empty space?
Even tinier particles!
Fundamental Particles
electric
charge
increasing mass
Quarks
Quarks
Leptons
Leptons
Generation
u
c
t
up
charm
top
d
s
b
down
strange
bottom
ne
nm
nt
e-neutrino
mu-neutrino
tau-neutrino
e
m
t
electron
muon
tau
I
II
III
2/3
-1/3
0
-1
All visible matter in universe is made of Generation I particles.
Held together by a powerful force:
STRONG FORCE
Four Fundamental Forces
fundamental particles interact by responding to a force from
another particle
FORCE
CARRIER
PARTICLE
gravity
graviton
leptons
weak
W+, W-, Z0
electromagnetic
photon
strong
gluon
quarks
And still more empty space….
filled with force fields
Atoms are 99.999999999999% empty space !!
World of Atoms – a little background education
Atom: nucleus of neutrons & protons with orbiting electrons
go down one layer
Electron: very light particle with negative charge
Proton: weight equals ~2000 electrons, positive charge
Neutron: weight almost equal to proton, no net charge
go down one layer
Quarks: fundamental particles, 6 types,
up/down/strange are the lightest and most common
Forces: strong, electromagnetic, weak, gravity;
strong force holds quarks together
go down one layer ???
is there another layer ???
Structure
of
Matter
World of Atoms – a little background education
we are more “empty space” than matter,
“empty space” is filled with carefully balanced forces,
get students to expand on the solar system model of atoms
great Web pages for students:
http://www.particleadventure.org
http://education.jlab.org
http://www2.slac.stanford.edu/vvc
great Web pages for teachers:
http://www.colorado.edu/physics/2000
http://www.fnal.gov/pub/education/k-12_programs.html
http://csee.lbl.gov
http://www.nsta.org
What really cool, tiny stuff do we study?
What forces hold the neutrons and protons together in an atom?
What forces hold the quarks inside a proton together?
How is electric charge distributed within a neutron or proton?
How is magnetic field distributed within a neutron or proton?
Does a “free” quark behave the same as a quark bound inside a
proton?
Does a “free” quark behave the same as a quark bound inside a
heavy atom?
Jefferson Lab’s Scientific Purpose
Study how quarks and gluons combine to form
protons and neutrons
Study how protons, neutrons, and electrons combine to form atoms
Jefferson Lab Lay-out
accelerator schematic
• Dept. of Energy Laboratory
• ~700 employees
• >2000 scientists from 18 countries
aerial photo
• 7/8 mile racetrack
• superconducting
• 3 experimental Halls
• 6 billion electron volts
South Linac Cryomodules
Recirculation Arc Configuration
• Arc
10
Hall C
Detector Systems
study strange quarks in proton (G-zero)
~ $10 Million cost
~ 5 year construction
proton detectors
~ 5 year measurements
~ 50 ton weight
~ 20 feet height
superconducting magnet
electron beam
hydrogen target
What are we studying right now ?
How do strange quarks contribute
to the properties of the proton?
Do they contribute to the spin?
Are the strange quark’s electric
interactions different from their
magnetic interactions?
What have we learned lately ?
proton can take many shapes……
Pentaquark – 5 quark
combinations may exist?
quark’s spin doesn’t
match neutron’s spin
116 GeV CEBAF
12
Upgrade magnets
and power
supplies
CHL-2
Two 1.1
0.6 GV linacs
New cryomodules get new rf zones
FUTURE JEFFERSON LAB
GlueX / Hall D Detector
Barrel Lead Glass
Calorimeter Detector
Solenoid
Coherent Bremsstrahlung
Photon Beam
Time of
Tracking
Flight
Cerenkov
Counter
Target
Note that tagger is
80 m upstream of
detector
Electron Beam from CEBAF
Tagging spectrometer and photon beamline review
Jan 23-24, 2006
Architect’s rendering of Hall D complex
Hall D
Counting House
Cryo Plant
Service
Buildings
Tagging spectrometer and photon beamline review
Jan 23-24, 2006
SUMMARY
Jefferson Lab:
• studies how protons and neutrons make up the nucleus of atoms
• studies how quarks and gluons make up neutrons and protons
• collides electrons with atomic targets and measures the energy, speed,
and trajectory of scattered particles
for your students
• introduce the solar system model of the atom
• go further...introduce forces (gravity, weak, electromagnetic, strong)
• gee whiz factor!
– we are more “empty space” than matter
– there are incredible forces acting in that “empty space”
physics is a great career !
Nuclear Physics as a Career
• college degree(s) required in physics, math, or computer science
• possible career paths:
–
–
–
–
–
government laboratory scientist
university professor & researcher
computer firms
modeling economic trends on Wall Street
start-up technology companies (medical imaging, cryogenic helium…..)
• salary range at Jefferson Lab (comparable to university professors):
– Staff Scientist I (approx. $48,000 to $75,000)
– Staff Scientist II (approx. $60,000 to $95,000)
– Staff Scientist III (approx $75,000 to $120,000)