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Large Hadron Collider went online on Sept. 10 2008
27 km ring
Counter propagating proton beams accelerated to 7x1012 eV make 11,000
revolutions per second and collide in four points
1600 superconducting magnets are
cooled to 2 K by 96 tons of liquid helium
CMS detector
Era of Discovery with CMS Detector
TAMU Group
Teruki Kamon, Alexei Safonov, David
Toback
Special Colloquium, LHC…
Alexei Safonov
09/17/08 (Next Wednesday)
The signal : jets + leptons + missing Energy
LHC Days…
We will try to understand:
 The mechanism for generating masses
 The physics behind the scale of W, Z boson mass scale
~ electroweak scale
Mplanck>>MW
 Do we have any further evidence of grand unification?

The origin of dark matter
Is there any particle physics connection?
From B. Dutta’s talk
Precision Cosmology at the LHC
5
From R. Fries’ talk
Quantum Fields
M. Planck (1900) suggested that
energy in light comes in small
packets called ‘quanta’.
Energy of one quantum
 = frequency
E  h
These quantum packets behave
like particles.
The electromagnetic field can be
described by the action of these
force carrier particles, called
photons .
Photons are bosons with spin 1 and they are massless. They ‘couple’ to
electric charges and have no electric charge themselves.
Force carriers
transmit forces by
being exchanged
between particles.
Particles and Forces
Feynman diagrams
Electron7+ proton
interacting
Electron-positron


annihilation e  e  2
Electroweak Force
It could be shown that the weak force and the electromagnetic force are two
aspects of one unified electroweak force.
There are 3 spin-1 bosons which are force carriers of the weak force, the
W+, W– and Z0 bosons which are very heavy. They couple to all fermions.
Feynman diagram
for muon decay
Boson with mass 0 (e.g. photon):
force ~ 1/distance2, infinite range
W,Z bosons
with
Particles
and Forces
large mass:
8
Force acts only over distance < 0.01 fm
Quarks
1968 a Rutherford-like experiment (deep inelastic scattering) confirmed
that there are indeed quarks inside a proton.
1st generation
2nd generation
3rd generation
Surprise: they have fractional electric
charges +2/3 or -1/3. They feel both the
weak
strong force.
Particlesand
and Forces
9
There are six quarks in 3
generations:
(up,down)
(charm, strange)
(top,bottom)
+ their six antiquarks
Increasing mass from 0.002
GeV (up) to 174 GeV (top).
Gluons
The strong interaction between quarks through
exchange of another spin-1 boson: the gluon g.
‘Charges’ for the strong force are called color
charges. There are three of them and each quark
can carry all 3:
‘red’, ‘green’ and ‘blue’ (+ 3 anti colors for
antiquarks)
g
q
q
Careful: this is not the
same as color in
common language!
Gluons couple to the color of a particle.
Two kind of hadrons (‘quark atoms’) exist:
p
Quark + Antiquark = Meson
(e.g. pions)
3 Quarks = Baryon
(e.g.
proton,
neutron)
Particles
and Forces
10
Hadron are color neutral:
Colors of the quarks add
up to ‘white’
+
Matter is effected by forces or interactions (the terms are interchangeable)
There are four fundamental forces in the Universe:
gravitation (between particles with mass)
electromagnetic (between particles with charge)
strong nuclear force (between quarks)
weak nuclear force (that changes quark types)
The Standard Model
The Standard Model (SM) describes all these particles and 3 of 4 forces. We have
confirmed the existence of those in the laboratory experiments.
+ Higgs boson
Higgs has not yet been discovered
The mass is constrained from LEP
and Tevatron data:
114 GeV<MH<154 GeV
Precision Cosmology at the LHC
12
The Higgs Boson
One particle is left to discuss: the Higgs Boson is part of the Standard
Model, but it is very special.
Higgs Mechanism:
A field fills all of space because of a
mechanism called spontaneous symmetry
breaking. It ‘sticks’ to particles, making it
‘harder for them to move’. This is what gives
quarks and leptons their mass.
Spontaneous symmetry breaking
Credit: CERN
Physics
Particles and Forces
As a consequence, there
should also be a spin-0
boson,13the Higgs boson.
It has not been found yet.
Particle
Similar to the
celebrity effect
in a crowd.
H
DARK MATTER
Orbital Motion in the Milky Way
Differential Rotation
• Sun orbits around
Galactic center with
220 km/s
• 1 orbit takes approx.
240 million years
• Stars closer to the
galactic center orbit
faster
• Stars farther out orbit
more slowly
GM
v
r
GM ( r )
v
r
4 3
M ( r ) ~  r
3
v ~ r  (r )
Matter extends beyond
the visible disk!
There is much more matter than we see!
Dark matter dominates in all galaxies! > 90% of
mass is invisible
Dark matter halo
Fritz Zwicky 1898-1974
Walter Baade 1893-1960
"spherical bastards”
What is dark matter???
•
•
•
•
•
•
White dwarfs
Brown dwarfs
Black holes
Neutrinoes
???
Revision of the Standard Model seems to
be necessary
The Early History of the Universe (2)
Protons and neutrons form a few 25% of mass in helium
helium nuclei; the rest of protons 75% in hydrogen
remain as hydrogen nuclei
No stable
nuclei with
5 and 8
protons
 Almost
no
elements heavier
than helium are
produced.
The Nature of Dark Matter
Can dark matter be composed of normal matter?
• If so, then its mass would
mostly come from protons
and neutrons = baryons
• The density of baryons
right after the big bang
leaves a unique imprint in
the abundances of
deuterium and lithium.
• Density of baryonic matter
is only ~ 4 % of critical
density.
• Most dark matter must be non-baryonic!