Transcript divinity - Particle Theory Group

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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detection of high energy particles
positron in cloud chamber
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e
m
p
Pion picture in a streamer chamber; gas
glows brightly along the tracks of the
particles.
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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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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
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 
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W
W
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  
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
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c c c
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t t t

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 e 
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 e 
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W
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 e 
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W
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hierarchy of scales
10-17 cm
10-33 cm
Planck scale
GN ~lPl2 =1/(MPl)2
Electroweak scale
range of weak force
mass is generated (W,Z)
strong, weak, electromagnetic
forces have comparable strengths
1028 cm
Hubble scale
size of universe lu
16 orders of magnitude
puzzle
What kind of physics generates and
stabilizes the 16 orders of magnitude
difference between these two scales
1027 eV
1011 eV
10-33 eV
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unification of couplings
The gauge couplings of the Standard Model converge to an
almost common value at very high energy.
what’s up
with that?
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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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unification of couplings
 SUSY changes the slopes of the coupling constants
For MSUSY=1 TeV, unification appears at 3x1016 GeV
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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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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) 68
underground and in the sky
KamLAND neutrino detector
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The coming experiments 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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Space and time may be doomed. E. Witten
I am almost certain that space and time
are illusions. N. Seiberg
The notion of space-time is clearly something we’re
going to have to give up. A. Strominger
If you ask questions about what happened at very early
times, and you compute the answer, the answer is:
Time doesn’t mean anything. S. Coleman
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SCIENCE: The Glorious Entertainment
…for any important assertion evidence must be produced;
…prophecies and bugaboos must be subjected to scrutiny;
… guesswork must be replaced by exact count;
….accuracy is a virtue and inquiry is a moral imperative.
To the hegemony of science we owe a feeling for which there
is no name, but which is akin to the faith of the innocent that
the truth will out and vindication will follow.
In its purest form science is justice as well as reason.
Jacques Barzun
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“let there be light”
is what we say when the experiment starts taking data ; usually in particle
physics and astronomy/cosmology
wednesday lunch
oct 9 2002
maria spiropulu
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