Future Directions in Particle Physics

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Future Directions in Particle Physics

• Physical and Biological Sciences Staff Lecture,
  UCSC

Michael Dine May 2006
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http//www4.nationalacademies.org/news.nsf/isbn/03
09101948?OpenDocument
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• Particle physics is a major activity in this
  division, centered around the Santa Cruz
  Institute for Particle Physics, SCIPP
• Experiment 5 regular faculty, 3 adjuncts, 10
  postdocs, researchers, 12 graduate students, 5
  technical staff
• Theory 3 faculty, two postdocs, 5 graduate
  students
• Staff 2
• (These are rough numbers)

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What is particle physics?
Particle physics is just that the study of
particles. What are the proton and neutron?
What are they made of? What about the electron?
How do all of these particles interact with each
other? The tools mainly big machines,
particle accelerators.
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Why Bother?

• No direct applications in the forseeable future
  (spinoffs include accelerator technologies in
  medicine, WWW, but one doesnt engage in such an
  endeavor to produce spinoffs).
• Learning about the elementary particles, we
  learn what are
• the laws of nature which operate at very
  small distance
• scales.
• Knowing the laws allows us to understand the
  universe

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Gravitation
Laws of Nature

• Newton Fma mM/R2
• Probably the most famous physical laws.
  UNIVERSAL

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Newton could use his laws to explain the motion
of the planets, the moon. Haley comets.
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Electricity and MagnetismFaraday
Laws of Nature
Conducted experiments which showed that a
changing electric field produces a magnetic
field and vice versa, and that a changing
magnetic field induces current (generators)
Electricity and magnetism aspects of one related
set of phenomena ELECTROMAGNETISM.
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Electricity and MagnetismMaxwell
Laws of Nature
Wrote down the laws of electricity and
magnetism Maxwells equations. Light, radio
waves (Maxwell predicted), and other radiation
all part of the same set of phenomena.
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HERTZ RADIO WAVES
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The end of the 19th century saw the discovery of
the first elementary particle, by Thompson the
electron.
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EINSTEIN
Laws of Nature
Excited by Maxwells equations and also puzzled.
There seemed to be a maximal speed at which light
could travel. Puzzled, also by the problem of
the photoelectric effect the emission of
electrons by light. 1905 SPECIAL RELATIVITY
time and space are relative concepts, depend on
the observer. But the speed is absolute all
observers agree about it. Not important when v
c, but very important in the day-to-day lives of
particle physicists.

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General Relativity
Now, a deeper understanding of the laws of
electricity and magnetism. But Einstein didnt
know how to reconcile Newtons laws with the
rules of relativity. Einsteins clue the
equality of gravitational and inertial mass
Fma FG mM/R2 Inertia something
to do with space and time. So gravity?
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Einstein and the General Theory of Relativity

• After almost eleven years of struggle, Einstein
  announced his general theory of relativity in
  1916. A theory in which gravity arises as the
  distortion of space and time by energy.
  Proposed three experimental tests
• Bending of light by the sun
• Perihelion of Mercury
• Red Shift
• Recent years pulsar timing (Thorsett), LIGO
  (Barish, Seiden)

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LIGO (searching for gravitational waves) Barish,
Seiden
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New particles, new laws

• 1911 - discovery of the atomic nucleus
• 1920s quantum mechanics
• 1930s the neutron, and understanding of the
  atomic nucleus.
• 1930s discovery of antimatter.

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Rutherfords Discovers the Nucleus (not quite an
accelerator)
"It was quite the most incredible event that ever
happened to me in my life. It was almost as
incredible as if you had fired a 15-inch shell at
a piece of tissue paper and it came back and hit
you."
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LOOKING STILL DEEPER

• By the 1940s, much progress, but much not well
  understood
• Photons
• The precise laws underlying the nuclear forces
• To go further theoretical developments
• Experiments probing distances smaller
• than the size of nuclei

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Quantum Electrodynamics

• Feynman, Schwinger, Tomanaga detailed
  understanding of how quantum mechanics and
  electricity and magnetism work together.
  Predictions with awesome precision. E.g. the
  magnetism of the electron explained in terms of
  the electrons charge and mass to one part in
  1012.

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The Accelerator Era

• The late 1940s launched the era of large
  particle accelerators. Some of the important
  discoveries (also cosmic rays)
• Particles like the electron, but heavier m t
• Three kinds of neutrino
• Neutrons, protons made up of quarks

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Stanford Linear Accelerator
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Quarks were discovered at SLAC, in an experiment
much like Rutherfords.
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SPEAR collided electrons and positrons
(anti-electrons) producing a previously unknown
form of matter, made of a new type of quark, the
charmed quarks (1974).
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• Experiments at SLAC and other accelerators
  established the full Standard model
• Brookhaven, Fermilab more quarks (b,t)
• SLAC, LEP The Z boson (Lidtke, Johnson, Schumm,
  Coyne, Seiden, Sadrozinski, )
• SLAC Studies of the asymmetry between
  antimatter and matter (BaBar Schumm, Seiden.)

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• quantum field theory, describing interactions
  between
• pointlike spin-1/2 particles (quarks and
  leptons)
• via exchange of spin-1 vector bosons (photon, W
  and Z, gluon)
• fundamental particles (fermions)
• 2 (particle pair)
• 3 (generations)
• 2 (anti-particles)

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quark masses and breaking of symmetry ?
why this pattern
1 GeV proton mass
electrical charge
2/3
-1/3
-1/3
-1/3
2/3
2/3 (?)
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Mw82Mz91
... weakest force ... ... irrelevant in
microcosm ...
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• Back to theory.
• Theorists played crucial role in development of
  the Standard Model
• Feynman, Gell-Mann quarks
• Gross, Politzer, Wilczek, t hooft developed
  and understood detailed theory of interactions
• Local theorists Banks (work on how quarks are
  bound into protons and neutrons), Dine
  (calculation of total rate of electron-positron
  collisions at SLAC), Haber (Higgs phenomenology),
  Primack (high energy interactions of quarks) all
  made contributions (in their youths!)

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Are we satisfied with the Standard Model? -- Yes
and no. Incredibly successful. At this moment,
no interesting discrepancies in hundreds of
measurements, many to part in 1000.
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• But puzzles
• Many parameters (masses of the particles,
  strengths of the interactions between particles).
  Where do they come from?
• The mass of the Higgs particle is very difficult
  to understand. We know its not much heavier
  than the W and Z. But according to principles of
  quantum mechanics, it should be much heavier.
• General relativity gravitation cant be
  sensibly combined. Some have even argue that
  General Relativity shows that quantum mechanics
  must be incomplete.

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One proposal for new physics Supersymmetry A
possible new symmetry of nature. Explains why
Higgs is light explains strength of the strong
interactions. Makes dramatic predictions for
experiments. A symmetry between bosons
(photon, gluons, Ws and Zs) and fermions
(electrons, quarks, neutrinos).
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... doubled particle spectrum ... ?
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Extensive searches so far havent seen.
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• The theorists at UCSC have all worked on
  supersymmetry, and made significant
  contributions
• Dine one of the first to build models of
  supersymmetry and consider their phenomenology at
  accelerators developed the theory of
  supersymmetry breaking
• Haber developed the phenomenology of
  supersymmetry at accelerators in some detail
• Banks models of supersymmetry, supersymmetry
  breaking, connections to string theory (more
  later)
• Primack more in a moment

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Back to Experiment
Many other ideas to address these problems. All
suggest new particles with masses of order 1000
times mp, or about 1 TeV (mc2). Where to find
them? The LHC. Beginning operation in late
2007. If supersymmetry, other hypotheses are
correct, we will know in a few years.
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CDF DØ data taking e 90
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CMS
ATLAS
LHC dipoles
LHC quadrupoles
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• Precise tracking and vertexing
• new bigger silicon/fiber tracker, new drift
  chamber, TOF
• Upgraded calorimeter and muon system
• Upgraded DAQ/trigger
• 670 - 750 physicists

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• Precise tracking and vertexing
• silicon pixel and strip detectors
  transition radiation det.
• 2 4 T solenoid and toroid magnets (air core
  or iron core)
• EM Had Calorimeters and muon systems
• Fast DAQ/trigger
• 1 600 physicists each

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Particle Physics and the Big Bang These are
puzzles in our understanding of the laws. There
are also puzzles in our understanding of the
universe. Dont have time to describe the Big
Bang, but this is an area where UCSC theorists
spend much of their research time (Aguirre,
Banks, Dine, Primack). Here just note that from
detailed astronomical and astrophysical
observations we know that the universe, billions
of years ago, was smaller and very hot. In the
last decade we have learned a great deal about
the composition of the universe
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COMPOSITION OF THE UNIVERSE

• From studies of CMBR, of distant Supernova
  explosions, and from Hubble and Ground-Based
  observations we know
• 5 Baryons (protons, neutrons)
• 30 Dark Matter ??? (zero pressure)
• 65 Dark Energy ???? (negative pressure)

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New York Times April, 2003

• Reports a debate among cosmologists about the Big
  Bang.
• lll1.html

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Rounding out the field were Dr. Lee Smolin, a
gravitational theorist at the Perimeter Institute
for Theoretical Physics in Waterloo, Ontario,
whom Dr. Tyson described as "always good for an
idea completely out of left field - he's here to
stir the pot"
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But Dr. Smolin said the 20th-century revolution
was not complete. His work involves trying to
reconcile Einstein's general relativity, which
explains gravity as the "curvature" of
space-time, with quantum mechanics, the strange
laws that describe the behavior of atoms.
"Quantum mechanics and gravity don't talk to
each other," he said, and until they do in a
theory of so-called quantum gravity, science
lacks a fundamental theory of the world. The
modern analog of Newton's Principia, which
codified the previous view of physics in 1687,
"is still ahead of us, not behind us," he said.
Although he is not a cosmologist, it was fitting
for him to be there, he said, because "all the
problems those guys don't solve wind up with us."
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• But Smolin is wrong. The proper address is
  particle physics.
• Origin of the baryons again, can be understood
  if supersymmetry (Dine).
• Dark matter we know that this is some new type
  of elementary particle. In supersymmetry,
  automatically a particle which plays this role
  (Primack Banks, Dine, Haber). Another
  candidate axions (Dine). Both subject of
  experimental search.
• Dark energy much harder. Only theoretical
  structure currently available string theory
  (Aguirre, Banks, Dine)

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String Theory
Smolin states we dont know how to reconcile
quantum mechanics and general relativity. But we
have known for a long time that a theory where
the basic entities are strings (rather than point
particles) looks a lot like the Standard Model
plus general relativity. Obeys all of the rules
of quantum mechanics.
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Strings colliding
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At first glance, the theory is very attractive.
Has Einsteins theory, quarks, leptons, gauge
bosons. Much pretty mathematics. Pretensions to
explain all of the parameters of the Standard
Model (masses and couplings). Has supersymmetry,
candidates for dark matter and dark energy. Some
very interesting physics and mathematics. But
much which is not understood. Banks, Dine
focus on how to extract predictions for processes
which can be studied in accelerators or the
cosmos. Esp. supersymmetry in accelerators, and
cosmology of the extremely early universe.
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The future The ILC

• long linac constructed of many RF accelerating
  structures
• typical gradients range from 25?60 MV/m
• single shot
• One working machine
  SLC at SLAC
  ? proof of
  principle

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International Linear Collider
Aug 2004 Technology decision

• Baseline
• 200 GeV lt vs lt 500 GeV
• Integrated luminosity 500 fb-1
  in 4 years
• 80 e- beam polarisation
• Upgrade to 1TeV, ?L 1 ab-1 in 3 years
• 2 interaction regions
• Concurrent running with the LHC from 2015

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PDG Wall Chart
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Detailed study of the CMBR

• From satellites and earth based (balloon)
  experiments. Most recently the WMAP satellite.

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Detailed information about the universe
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