Future Directions in Particle
Physics
Physical and Biological Sciences
Staff Lecture, UCSC
Michael Dine
May 2006
http://www4.nationalacademies.org/ne
ws.nsf/isbn/0309101948?OpenDocume
nt
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)
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.
Why Bother?
No direct applications in the forseeable future (spinoffs include
accelerator technologies in medicine, WWW, but one doesn’t
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
Laws of Nature:
Gravitation
Newton: F=ma = mM/R2
Probably the most famous physical
laws. UNIVERSAL
Newton could use his laws
to explain the motion of the
planets, the moon. Haley –
comets.
Laws of Nature:
Electricity and Magnetism:
Faraday
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.
Laws of Nature:
Electricity and Magnetism:
Maxwell
Wrote down the laws of electricity
and magnetism; Maxwell’s equations.
Light, radio waves (Maxwell predicted),
and other radiation all part of the same
set of phenomena.
HERTZ: RADIO WAVES
The end of the 19th century saw the discovery of the first
elementary particle, by Thompson – the electron.
Laws of Nature:
EINSTEIN
Excited by Maxwell’s 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.
General Relativity
Now, a deeper understanding of the laws of
electricity and magnetism. But Einstein didn’t
know how to reconcile Newton’s laws with the rules
of relativity.
Einstein’s clue: the equality of gravitational and
inertial mass:
F=ma
FG= mM/R2
Inertia – something to do with space and time. So
gravity?
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)
LIGO (searching for gravitational
waves) [Barish, Seiden]
New particles, new laws
• 1911 - discovery of the atomic nucleus
• 1920’s – quantum mechanics
• 1930’s – the neutron, and understanding of
the atomic nucleus.
• 1930’s – discovery of antimatter.
Rutherford’s 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 15inch shell at a piece of tissue paper and it came back and hit you."
LOOKING STILL DEEPER
By the 1940’s, 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
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
electron’s charge and mass to one part in
1012.
The Accelerator Era
The late 1940’s 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
Stanford Linear Accelerator
Quarks were discovered at
SLAC, in an experiment much
like Rutherford’s.
SPEAR collided electrons and positrons (antielectrons) producing a previously unknown
form of matter, made of a new type of quark,
the charmed quarks (1974).
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….)
The Standard Model (I)
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)
1995
2000
The Standard Model (II)
quark masses
and breaking of symmetry ?
why this
pattern
1 GeV= proton mass
electrical charge
+2/3
-1/3
-1/3
+2/3
-1/3
+2/3 (?)
Fundamental Interactions
Mw=82;Mz=91
... weakest force ...
... irrelevant in
microcosm ...
9.
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!)
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.
Electroweak Precision Data
... need to consider
quantum fluctuations ...
MZ2 = MZ2 0.order / (1 - Δ)
Δ
comparison :
precision measurement ⇔ correction
⇨prediction of mass of top quark
... mt2 ... + ... ln mh ...
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 it’s not
much heavier than the W and Z. But
according to principles of quantum
mechanics, it should be much heavier.
•General relativity – gravitation – can’t be
sensibly combined. Some have even argue
that General Relativity shows that quantum
mechanics must be incomplete.
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,
W’s and Z’s) and ``fermions” (electrons, quarks,
neutrinos…).
An attractive Extension: Supersymmetry
Symmetry between
Fermions ↔ Bosons
(matter)
(force carrier)
... doubled particle spectrum ... ☹
l
g
q
l
~
q
g
~
g
l
Extensive searches; so far haven’t seen.
q
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
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.
The TEVATRON at Fermilab
Chicago
60 km
Booster
Tevatron
_
p source
p _
p
~ 1.5 fb-1
delivered
Main Injector
& Recycler
~ 1.2 fb-1
recorded
_
p
s =1.8 - 1.96 TeV, t = 396 ns
p
Run I 1987 (92)-95 Lint ~ 125 pb-1
Run II 2001-09
4-9 fb-1
9.March
Recent2006:
Results
Hadron
from the
Collider
Tevatron
Physics
-Selected
- ArnulfHighlightsQuadt – 2.11.2005,
UCSC
Arnulf
Colloquium
Quadt
CDF & DØ data taking ε ~90%
Page
Seite3838
The Large Hadron Collider - LHC
CMS
ATLAS
The Large Hadron Collider: _
proton-proton collider (no p)
⇨2 separate beampipes
first collisions in 2007
high energy: s = 14 TeV
40 Mio. collisions per second
4 experiments:
ATLAS, CMS, ALICE, LHC-B
10 fb-1 per year
9.March 2006: Hadron Collider Physics - Arnulf Quadt –
LHC dipoles
UCSC Colloquium
LHC quadrupoles
Page 39
The CDF & DØ Experiment
Precise tracking and vertexing
new bigger silicon/fiber tracker, new drift chamber, TOF
Upgraded calorimeter and muon system
Upgraded DAQ/trigger
~670 - 750 physicists
resolutions:
EM: σE/E = 13.5 - 15% / sqrt(E)
HAD: σE/E = 50 – 80 % / sqrt(E)
9.March 2006: Hadron Collider Physics - Arnulf Quadt –
UCSC Colloquium
Page 40
The CDF & DØ Experiment
9.March 2006: Hadron Collider Physics - Arnulf Quadt –
UCSC Colloquium
Page 41
The ATLAS & CMS Experiment
weight
height
length
magnet (solenoid)
7 000 t
22 m
42 m
2 Tesla
weight
height
length
magnet (solenoid)
12 500 t
15 m
22 m
4 Tesla
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
resolutions:
EM: σE/E = 0.5 - 10% / sqrt(E)
~ 1 600 physicists each
HAD: σE/E = 50 – 70 % / sqrt(E)
9.March 2006: Hadron Collider Physics - Arnulf Quadt –
UCSC Colloquium
Page 42
The ATLAS and CMS Experiment
9.March 2006: Hadron Collider Physics - Arnulf Quadt –
UCSC Colloquium
Page 43
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.
Don’t 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:
COMPOSITION OF THE
UNIVERSE
From studies of CMBR, of distant Supernova
explosions, and from Hubble and GroundBased observations we know:
• 5% Baryons (protons, neutrons)
• 30% Dark Matter [???] (zero pressure)
• 65% Dark Energy [????] (negative pressure)
New York Times: April, 2003
Reports a debate among cosmologists about
the Big Bang.
lll1.html
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";
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."
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)
String Theory
Smolin states we don’t 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.
Strings colliding
At first glance, the theory is very attractive. Has
Einstein’s 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.
The future: The ILC
e+
e10-20 km
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
Aug 2004: Technology decision
International Linear Collider
• Baseline:
200 GeV < √s < 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
PDG Wall Chart
Detailed study of the CMBR:
From satellites and earth based (balloon)
experiments. Most recently the WMAP
satellite.
Detailed information about the
universe: