1. Particle Physics what do we know?
Ulrich Heintz
Boston University
8/5/2002
Ulrich Heintz - Quarknet 2002

2. Ulrich Heintz - Quarknet 2002
Particle Physics
What associations does the word particle physics bring to your mind?
8/5/2002
Ulrich Heintz - Quarknet 2002

3. Ulrich Heintz - Quarknet 2002
Particle Physics
What are the fundamental building blocks of the universe?
What are the interactions between them?
How can we explain the universe?
its history
its present form
its future
Is there a theory of everything?
8/5/2002
Ulrich Heintz - Quarknet 2002

4. it’s fun and fascinating
Particle Physics
it’s fun and fascinating
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Ulrich Heintz - Quarknet 2002

5. Ulrich Heintz - Quarknet 2002
What is a particle?
a small piece of matter...
characterized by
charge
mass
lifetime
spin
particles can scatter off each other like billiard balls
unlike billiard balls, most particles are unstable and decay
particles can be produced by colliding other particles
8/5/2002
Ulrich Heintz - Quarknet 2002

6. What was the world made of in 1932?
electrons (1897)
orbit atomic nucleus
proton (1911)
nucleus of lightest atom
neutron (1932)
neutral constituent of the nucleus
photon (1905)
quantum of the electromagnetic field
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Ulrich Heintz - Quarknet 2002

7. Ulrich Heintz - Quarknet 2002
and...
1927 Dirac’s relativistic quantum mechanics
1931 the positive electron (positron)
antiparticles: for every particle there exists an antiparticle with same mass, lifetime, spin, but opposite charge
1930 Pauli’s neutrino
energy conservation in beta decay requires the existence of a light, neutral particle
n  p+ + e- + 
observed in 1956
the muon and the pions (+,0,-)
Rabi: “who ordered that?”
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Ulrich Heintz - Quarknet 2002

8. The ascent of accelerators
previous discoveries used
cosmic rays
“natural accelerators” (radioactivity)
after WWII
accelerators
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Ulrich Heintz - Quarknet 2002

9. Ulrich Heintz - Quarknet 2002
The particle “Zoo”
1947: strange particles
K0+ -, K++ + -
p+ -
, 
long lifetime  ¼ s
more particles...
p,

short lifetime  ¼ s
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Ulrich Heintz - Quarknet 2002

10. Ulrich Heintz - Quarknet 2002
The quark model
1964 Gell-Mann, Zweig
there are three quarks and their antiparticles
each quark can carry one of three colors
red blue green
antiquarks carry anticolor
anti-red anti-blue anti-green
Quark Up
Down
Strange
Charge
+2/3
-1/3
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Ulrich Heintz - Quarknet 2002

11. Ulrich Heintz - Quarknet 2002
The quark model
only colorless (“white”) combinations of quarks and antiquarks can form particles
qqq qq
no others observed
8/5/2002
Ulrich Heintz - Quarknet 2002

12. Ulrich Heintz - Quarknet 2002
The 8-fold way
baryons qqq
mesons qq 0 - + +
0  - 0
uss
uus
dss
dds
udd
uud
uds -
ddd
++
uuu -
sss n p K0 - K+ +
0   K- sd ud su du ds us
uu,dd,ss
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Ulrich Heintz - Quarknet 2002

13. Ulrich Heintz - Quarknet 2002
Quark confinement
What holds quarks/antiquarks together?
strong force
acts between all “colored” objects
short range
independent of distance
8/5/2002
Ulrich Heintz - Quarknet 2002

14. So what is the world made of?
The Standard Model e e u d
0.511 MeV
a few MeV   c s
106 MeV
1100 MeV
150 MeV   t b
1.8 GeV
175 GeV
4.2 GeV
spin = ½
(fermions)
leptons
quarks
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Ulrich Heintz - Quarknet 2002

15. Ulrich Heintz - Quarknet 2002
Are these fundamental?
As far as we know....
we can measure structure as small as m
Accelerators are like huge microscopes
To measure smaller distances
go to higher energies
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Ulrich Heintz - Quarknet 2002

16. How do particles interact?
particles attract or repel each other by exchanging “messenger” particles (field quanta) e  
Feynman
diagram
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Ulrich Heintz - Quarknet 2002

17. What holds the world together?
force
acts between
relative strength
field quantum
strong
quarks 10 g
electro-magnetic
charged particles
10-2 
weak
all particles
10-13
W§ Z0
gravity
all particles
10-42 G
spin = 1 (bosons)
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Ulrich Heintz - Quarknet 2002

18. Ulrich Heintz - Quarknet 2002
The Higgs boson
the standard model requires the existence of one more particle
Higgs boson
uncharged
unknown mass (>115 GeV)
spin = 0
required to be able to describe massive fermions and bosons
8/5/2002
Ulrich Heintz - Quarknet 2002

19. Is this the theory of everything?NO
Standard Model doesn’t work at all energies
Standard Model does not include gravity
we haven’t found the Higgs yet...
unification
Electricity
Magnetism
Weak force
Strong force
Gravity
electromagnetism
electroweak force
GUTs
string theory...
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Ulrich Heintz - Quarknet 2002

20. Ulrich Heintz - Quarknet 2002
Accelerators
1983: CERN pp collider
E = 540 GeV  W§ (80 GeV), Z0 (91 GeV)
1995: Fermilab Tevatron pp collider
E=1.8 TeV  top quark (175 GeV)
¼ 2008: CERN LHC pp collider
E=14 TeV  discover Higgs?
????: Linear e+e- Collider
E=1-2 TeV  study Higgs in detail
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Ulrich Heintz - Quarknet 2002

21. Ulrich Heintz - Quarknet 2002
What might we find?
Super Symmetry
fermions  bosons
we have already found half the particles....
electron
selectron
neutrino
sneutrino
quark
squark
photon
photino
gluon
gluino W
Wino Z
Zino
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Ulrich Heintz - Quarknet 2002