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2nd ANNUAL MEETING of the PRAIRIE SECTION of the AMERICAN PHYSICAL SOCIETYheld in conjunction with the Chicago Section of the American Association of Physics Teachers (CSAAPT)
Thursday, November 18, 7:00 p.m.Wishnick Hall AuditoriumIIT Main Campus, Chicago, IL
Students, faculty, alumni, IIT Community are welcome to this free public lecture.
The Large Hadron Collider provides the greatest leap in capability of any instrument in the history of particle physics. We do not know what it will find, but the discoveries we make and the new puzzles we encounter are certain to change the face of particle physics and to echo through neighboring sciences.
Join us as we welcome Chris Quigg, the highly respected physicist at the forefront of today’s revolutions in particle physics. His work ranges over many topics, from electroweak symmetry breaking and supercollider physics to heavy quarks and the strong interaction among them to ultrahigh-energy neutrino interactions.
THE COMING REVOLUTIONS IN PARTICLE PHYSICS
RSVP: Professor Christopher White | [email protected]
Theoretical Physics Department, Fermilab2011 J. J. Sakurai Prize for Theoretical Particle Physics Recipient
CHRIS QUIGG1
The Coming Revolutions in Particle Physics
Chris Quigg
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Atoms became real in the 20th century
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To explain a complicated visible by a simple invisible
Eric
Wee
ks, E
mor
y U
.
Jean Perrin
4
5
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All things are made of atoms–little particles that move around in perpetual motion, attracting each other when they are
a little distance apart, but repelling upon being squeezed
into one another.
—Richard Feynman, Six Easy Pieces
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Quantum Mechanics
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Great Lesson of XXth Century Science
The human scale of space & time is not privileged for understanding Nature . . .
and may even be disadvantaged
9
The world’s most powerful microscopes
Tevatron collider at Fermilabprotons on antiprotons at 1+1 TeV
speed of light: c ≈ 109 km/h (30 cm/nanosecond)speed of proton: c – 495 km/h
Protons pass my window 45,000 times / second>10 million collisions per second
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CDF Experiment
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CDF two-jet event (70% of energy ⊥ beam direction)
quark + antiquark → jet + jet
The World’s Most Powerful Microscopesnanonanophysics
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Walk of Ideas, Altes Museum Berlin (2006)
Lien
hard
Sch
ulz
(Wik
iped
ia)0
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D0 top quark + antiquark
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Accelerators as time machines …
15
Pointlike (r ≤ 10−18 m) quarks and leptons
Our Picture of Matter (the revolution just past)
uRdR
cRsR
tRbR
eR
R
R
uLdL
cLsL
tLbL
eLL
L12
3
1
2
3
d u
u
Gravitation, electromagnetism, radioactivity, strong interaction
16
New Law of Nature #1
Quantum chromodynamics (QCD): color symmetry among quarksred· green· blue gluons
d u
u
D. Leinweber
uRdR
cRsR
tRbR
uLdL
cLsL
tLbL
17
M78· SDSS
Lattice QCD: quark confinement origin of nucleon masshas explained nearly all visible mass in the Universe
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New Law of Nature #2
uLdL
cLsL
tLbL
eLL
Le
Electroweak theory:family symmetryu ↔ d ; ν ↔ e ; …
weak bosons (W+, W–, Z0) + photon
19
Weak interactions, electromagnetism seem so different …
Weak Electromagnetic
range: 1% proton size infinite range
W: 90 × proton mass massless photon
How can they share a common origin (symmetry)?
20
Symmetry of laws �⇒ symmetry of outcomes
Stud
ies
amon
g th
e Sn
ow C
ryst
als
... by
Wils
on B
entle
y, vi
a N
OA
A P
hoto
Lib
rary
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Meissner Effecthidden EM symmetry
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Superconductivity suggestsa field that permeates all of spacecould hide electroweak symmetry
Peter Higgs+ R. Brout, F. Englert, G. Guralnik, R. Hagen, T. Kibble
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Higgs boson: massive particle with spin zerohides electroweak symmetry
gives mass to W and Zgives mass to electron, quarks, etc.
Not yet observed!
Theory does not predict Higgs-boson mass
“Standard” Electroweak Theory
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Gedankenexperiment
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100 150 200 250 300
!! 2
0
2
4
6
8
10
12
LEP
excl
usio
n at
95%
CL
Teva
tron
exc
lusi
on a
t 95%
CL
Theory uncertainty
Fit including theory errors
Fit excluding theory errors
MH (GeV)
3!
2!
1!
G fitter SM
March 2009
Where the (standard) Higgs boson might be
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Large Hadron Collider· CERN
proton-proton collisions at 3.5 → 7 TeV/beam
LHCb
ATLASALICE
CMS
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CMS
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CMS
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CMS
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32
ATLAS
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Das LHC Projekt S.Bethke Max-Planck-Institut für Physik 3320
ATLAS
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ATLAS
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Fabiola Gianotti (ATLAS) : If we do not find the Higgs boson,that means that the theory is just wrong!
35
• New kind of force? (Higgs boson)
• New force from a new symmetry?
• Residual force from strong dynamics?
• Echo of extra spacetime dimensions?
Which path has nature taken?
What hides the electroweak symmetry?
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Why will it matter?
Understanding the everyday …
Why atoms? Why chemistry? Why stable structures?
37
Without a Higgs mechanism …
Electron and quarks would have no massQCD would confine quarks into protons, etc. Proton mass little changedSurprise: QCD would hide EW symmetry, give tiny masses to W, ZMassless electron: atoms lose integrity No atoms means no chemistry, no stable composite structures like liquids, solids, …
… character of the physical worldwould be profoundly changed
38
Much more to learn …
39
Revolution: the meaning of identity
• What makes a top quark a top quark and an electron an electron?
• What sets masses of quarks & leptons?
40
!"#$
!"#%
!"#&
!"#'
!"#(
!"#!
!""
)*++,-.*/01*2.
13*45.6 2.789:+
;7 <;*4/+
69=: <;*4/+
.
;6
1
+
8
>
!
"
Higgs boson knows something we don’t know!41
KATRIN aims at 0.2 eV
42
Strings?
1018
Planck scale
Quantum gravity?
[A PUZZLE RAISED BY THE HIGGS]
Unexplained gap
Limit of LHC
Strong-electro
weak
uni!cation sc
ale?
Electroweak scale
Electron
Neutrino masses
Muon
Top
Bottom
Tau
Charm
Proton
Neutron
10–6
10–3
100
103
106
109
1012
1015
10–9
HiggsUp Down
Strange ZW
H
Energy Scale (GeV)
An electroweak puzzle:Does MH < 1 TeV make sense?The peril of quantum corrections
Scientific American
43
How to separate electroweak, higher scales?
Extend electroweak theory on the 1-TeV scale …
composite Higgs boson
technicolor / topcolor
supersymmetry
…
Ask instead why gravity is so weak
44
MPlanckM*1/R(1 mm)�–1
1 TeV
Stre
ngth
of F
orce
s3-2-1
LED
Conventional Gravity
Suppose at scale R … gravity propagates in 4+n dimensions
1/r 2
1/r 2+n
MPlanck would be a mirage!45
Range !G (meters)
Lamoreaux
Irvine
Eöt-Wash
Boulder
10–6 10–5 10–4 10–3 10–2
108
104
100
10–4
Rel
ativ
e S
tren
gth "
G
Stanford
Gravity follows Newtonian force law down to ≲ 1 mm
1 0.110E (meV)A
nom
alou
s C
oupl
ing
46
Another “minor” problem
• Higgs field fills all of space with energy density 1028 g/liter
• But empty space weighs next to nothing: < 10-26 g/liter
• New evidence that vacuum energy is present (accelerating universe)
47
New physics in the LHC range?More
If dark matter interacts weakly …
… its likely mass is 0.1 to 1 TeV
COSMOS
48
Dark matter relics of the big bang?
49
Revolution:Unity of Quarks & Leptons
•What do quarks and leptons have in common?
•Why are atoms neutral?
50
Conjectured Law of Nature?
eLL
Le
uLdL
cLsL
tLbL
A symmetry among quarks and leptons …… would have to be a hidden symmetry
eLL
Le
uLdL
cLsL
tLbL
Extended quark–lepton families: proton decay!
51
SU(3)c
SU(2)L
U(1)Y
log10
�E
1 GeV
�
1/α
60
40
20
0 5 10 15
Unification of Forces?
52
Connections …
53
ALICE Experiment: Pb-Pb Collisions at 287 TeV
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?55
“It was as if, suddenly, we had broken into a walled orchard, where protected trees had flourished and all kinds of exotic fruits had ripened in great profusion.”
— Cecil Powell1950 Nobel Prize
56
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Thanks to …
Eric Weeks for the film of Brownian motion www.physics.emory.edu/~weeks
J. D. Jackson for the photo of Peter Higgs
58
