Download aspen_pb - Particle Theory

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Invasions in Particle Physics
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Invasions?
“Gentlemen we are being invaded:
the accelerators are here”
L.Leprince-Ringuet
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Particle Physics - High Energy Physics
High energy particles have extremely small wavelengths and
can probe subatomic distances: high energy particle
accelerators serve as super-microscopes.
The higher the energy the closer particles can come to each
other, revealing the smaller details of their structure.
The energy of the collisions produces new particles : E=mc 2
The higher the energy the heavier the new particles that can be
created.
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like smashing two cars together
and getting a bulldozer out
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21st century particle physics
(e.g.) Fermilab’s Tevatron is the highest
energy accelerator in the world today.
Beams of protons collide with beams
of antiprotons
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antimatter
 particle accelerators create antimatter by smashing
high energy particles onto metals
 the total amount of antimatter produced in particle
accelerators per year ~ 1 microgram
 even one microgram of antimatter would provide
enough energy to drive your car for a month (E=mc2)
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The SNO detector is more than a mile underground
no mass?
 Yes, photons are massless
 We thought neutrinos were massless too
 In 1998 underground experiments
discovered that neutrinos have tiny masses
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32?
7?
6? extra dimensions?
Experiments can actually
discover them!
String theory demands extra
dimensions.
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In 1905 Victor Hess performed a
series of high-altitude balloon
experiments and found ionizing
radiation the origin of which is
beyond the Earth’s atmosphere.
Cosmic rays were the only source
of high energy particles to study
until accelerators were developed.
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Where does this proton come from?
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one possible source of such
high-energy protons:
two rings of high-energy
particles created from
matter from the supernovae
remnant falling towards the
black hole.
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detection of high energy particles
positron in cloud chamber
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CLOUD (WILSON) CHAMBER
The chamber creates a volume of supersaturated alcohol
vapor that condenses on ions left in the wake of charged
particles. This is accomplished by establishing a steep
vertical temperature gradient with dry ice. Alcohol
evaporates from the warm top side and diffuses toward
the cold bottom. A layer of supersaturation is created
near the chamber bottom. Tracks of alcohol droplets
indicate trajectories of charged particles, since each ion
becomes a nucleation site for droplet condensation.
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the pion
electron (e)
(p)
(m)
particle tracks left in a photographic emulsion during the
decay of a pion.
 The pion enters moving upwards and comes to rest.
 It decays to produce a muon, which travels to the right.
 The muon then decays to an electron, producing the final track
leaving at the top right.
The pion was discovered by Cecil Powel and Giuseppe Occhialini in 1947 using
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photographic emulsions at the Pic du Midi, high in the French Pyrrenees.
p.s. e, m are leptons
e
m
p
Pion picture in a streamer chamber; gas
glows brightly along the tracks of the
particles.
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Strange Particles
 All of these strange particles were unstable.
Their origin and purpose was an entire mystery.
There were two kinds of them: one kind whose decay products
included always a proton were called hyperons and one kind
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whose decay products only consisted of pions were called kaons.
Jack Steinberger
“ I remember in 1949, on a
bulletin board at the Princeton
Institute for Advanced Study, a
photomicrograph of a nuclear
emulsion event, showing what is
now known a a K-meson decaying
into three pions. We all saw it. No
doubt that something interesting
was going on, very different from
what was then known, but it was
hardly discussed because no one
knew what to do with it”
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linear accelerators
:
The Norwegian Rolf Wideröe realized that, if the phase of the
alternating voltage changed by 180 degrees during a particle’s
trip between gaps, the particle could gain energy in each gap.
The idea of the linear accelerator was born.
Wideroe Principle
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1st circular accelerator
(11 inches!)
 uses both electric and
magnetic fields.
 particles orbit in circles
Lawrence and Livingston built the
first cyclotron in 1932. It was about
30 cm across, in a magnetic field of
about 5000 Gauss and accelerated
protons to roughly 1.2 MeV
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professor’s view
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mechanical engineer’s view
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computer scientist’s view
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theoretical physicist’s view
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visitor’s view
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Synchro-cyclotron, Betatron, synchrotron
Lawrence
McMillan
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LBL
Cosmotron
3 GeV protons Brookhaven National Laboratory(1952)
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major invasions in accelerator technology
 Strong Focusing (1952)
 Colliding Beams (60s)
 Superconducting magnets (80s)
 Stochastic Cooling (80s)
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P2K/NASATV movie excerpt
After the pion a plethora of new particles called
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hadrons were discovered in accelerators
All hadrons are made of quarks
uud
p
uus S+
uss
udd n
uds S0/L0 dds S-
X0
dss X-
strangeness
S=0
name
nucleon
S=-1
sigma
S=-2
cascade (ksi)
The baryon octet
up quark : u down quark : d strange quark : s
strangness then is counting how many strange quarks are in these hadrons
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quarks
 quarks have not been seen as isolated particles.
 when you smash hadrons at high energies where you expect
a quark, what you observe downstream is a lot more hadrons,
NOT fractionally charged quarks.
 this spray of hadrons is called “jet”
Gell-Man 1964:
“A search for stable quarks… and/or stable
di-quarks … at the highest energy accelerators would help to
reassure us of the non-existence of real quarks”
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the Big picture
The universe is made out of matter particles
and held together by force particles
fermions
quarks
leptons
bosons
gauge
bosons
graviton
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Feynman Graph
The electron and quark interact electromagnetically by
the exchange of a photon. The lines, wiggles and
vertices represent a mathematical term in the
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calculation of the interaction.
Quantum Weirdness
 The interactions of particles obey the rules of quantum
mechanic and of special relativity
 And particles aren’t really particles, they are quantum
fields
 The fermions (quarks and leptons) are especially
weird…
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Guess
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the Model
What is a model?
After 50 years of effort, we have a quantum theory
which explains precisely how all of the matter particles
interact via all of the forces — except gravity.
For gravity, we still use Einstein’s General Relativity,
a classical theory that has worked pretty well because
gravity effects are so weak.
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the Standard Model
a list of particles with their “quantum numbers”,
about 20 numbers that specify the strength of the
various particle interactions,
a mathematical formula that you could write on a
napkin.
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e
 e 
e 
  e
u u u
d d d
u u u
 m 
 
m  L
d d d
Z
0
W
W
m
m
  
 
 
  L


c c c
s s s
c c c
t t t
b b b
t t t
s s s
t t t
+
-

g
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e
 e 
e 
  e
u u u
d d d
u u u
 m 
 
m  L
d d d
Z
0
W
W
m
m
  
 
 
  L


c c c
s s s
c c c
t t t
b b b
t t t
s s s
t t t
+
-

g
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e
 e 
e 
  e
u u u
d d d
u u u
 m 
 
m  L
d d d
Z
0
W
W
m
m
  
 
 
  L


c c c
s s s
c c c
t t t
b b b
t t t
s s s
t t t
+
-

g
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e
 e 
e 
  e
u u u
d d d
u u u
 m 
 
m  L
d d d
Z
0
W
W
m
m
  
 
 
  L


c c c
s s s
c c c
t t t
b b b
t t t
s s s
t t t
+
-

g
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what does the Standard Model explain ?
your body  atoms  electrons
protons, neutrons  quarks
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what does the Standard Model explain ?
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neutrino () sky
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what does the Standard Model explain ?
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what does the Standard Model not explain ?
 quantum gravity
HST image of an 800 light-year wide spiral shaped
disk of dust fueling a 1.2x10^9 solar mass black hole
in the center of NGC 4261
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what does the Standard Model not explain ?
 quantum gravity
 dark matter and dark energy
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what does the Standard Model not explain ?
 quantum gravity
 dark matter and dark energy
 Higgs
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Arrange it so delicately that it will fall down in 19 minutes.
the Bigger Big picture
The Standard Model describes everything that we have
seen to extreme accuracy.
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the Bigger Big picture
Now we want to extend the model to
higher energies and get the whole picture
For this we need new experiments and ideas
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Dirac (1928)
matter
antimatter
special relativity & quantum mechanics
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supersymmetry (SUSY)
fermions
bosons
every particle has a superpartner particle
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supersymmetry
fermions
bosons
every particle has a superpartner particle
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supersymmetry
fermions
bosons
electron
quark
photino
gravitino
selectron
squark
photon
graviton
 none of the sparticles have been discovered yet
 most of the dark matter
in the universe maybe
the lightest sparticle
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what do
explain ?
 quantum gravity
HST image of an 800 light-year wide spiral shaped
disk of dust fueling a 1.2x10^9 solar mass black hole
in the center of NGC 4261
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 require 7 extra space dimensions
 and give us ways to hide them
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compactification
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brane-worlds
There could be
other branes which
would look like
dark matter to us
Standard Model particles are trapped on a brane and
can’t move in the extra dimensions
how do we see a hidden dimension?
? what particles can move in that dimension
? how big is that dimension
? what is its shape
some dimensions are easier to detect than others
slice of a
6 dimensional
Calabi-Yau space
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gravitons
are the most robust probe of extra dimensions
gravity is so weak that we have never
even seen a graviton.
melectronmelectron
F=GN
r2
melectron
r
melectron
The gravitational attraction between two electrons is
about 1042 times smaller than the electromagnetic
repulsion.
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think about this:
gravity gets stronger at extremely high
energies (or short distances).
it gets stronger at lower energies if
there are extra dimensions….
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…in which case high energy gravitons
may be produced in collider experiments:
quark
gluon (becomes
“jet” of hadrons)
antiquark
graviton
these gravitons probably “escape”
into the extra dimension(s)
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graviton emission simulation:
 we don’t see the graviton
 we see a jet from the gluon
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Collider Detector at Fermilab
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concentric cylindrical layers
energy deposited from the particle debris
of the collision in the middle
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“lego” event display
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Two events are graviton
simulation and one is
real CDF data: Can you
pick the gravitons?
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two events are real CDF
data and one is graviton
simulation; Can you
pick the graviton?
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supersymmetry at colliders
~χ 0
1
~χ 0
1
gluino and squark particles:
production and decays
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e.g.
SUSY candidate event at CDF
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Higgs simulation
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new accelerators for new physics
Linear Collider (?,~2012)
Large Hadron Collider (CERN, 2006)
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underground and in the sky
SuperNova Acceleration Probe (SNAP) 80
underground and in the sky
KamLAND neutrino detector
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The coming invasions in particle physics, cosmology
and astrophysics will answer (among many other
questions)
 what is the physics that connects the gravitational scale and the
scale of the typical mass of the elementary particles
 what is dark energy and what is dark matter
 do protons decay
 what is string theory
 what are the dimensions and dynamics behind spacetime
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