Large Hadron Collider went online on Sept. 10 2008 Counter propagating proton beams accelerated to...
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Transcript of Large Hadron Collider went online on Sept. 10 2008 Counter propagating proton beams accelerated to...
Large Hadron Collider went online on Sept. 10 2008
Counter propagating proton beams accelerated to 7x1012 eV make 11,000 revolutions per second and collide in four points
27 km ring
CMS detector
1600 superconducting magnets are cooled to 2 K by 96 tons of liquid helium
Era of Discovery with CMS DetectorEra of Discovery with CMS Detector
TAMU Group Teruki Kamon, Alexei Safonov, David
Toback
Special Colloquium, LHC… Alexei Safonov09/17/08 (Next Wednesday)
The signal : jets + leptons + missing Energy
LHC Days…
5
The mechanism for generating masses
We will try to understand:
The physics behind the scale of W, Z boson mass scale ~ electroweak scale
The origin of dark matter
Do we have any further evidence of grand unification?
Is there any particle physics connection?
Precision Cosmology at the LHC
Mplanck>>MW
From B. Dutta’s talk
Particles and Forces 7
Quantum FieldsM. Planck (1900) suggested that energy in light comes in small packets called ‘quanta’.
These quantum packets behave like particles. The electromagnetic field can be described by the action of these force carrier particles, called photons .
Energy of one quantum
= frequency
Force carriers transmit forces by being exchanged between particles.
Photons are bosons with spin 1 and they are massless. They ‘couple’ to electric charges and have no electric charge themselves.
Electron + proton interacting
Electron-positron annihilation
Feynman diagrams
2 ee
hE
From R. Fries’ talk
Particles and Forces 8
Electroweak Force
Boson with mass 0 (e.g. photon): force ~ 1/distance2, infinite range
W,Z bosons with large mass:Force acts only over distance < 0.01 fm
Feynman diagram for muon decay
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.
Particles and Forces 9
Quarks1968 a Rutherford-like experiment (deep inelastic scattering) confirmed that there are indeed quarks inside a proton.
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).
1st generation
2nd generation
3rd generation
Surprise: they have fractional electric charges +2/3 or -1/3. They feel both theweak and strong force.
Particles and Forces 10
GluonsThe strong interaction between quarks through exchange of another spin-1 boson: the gluon g.
g
q q
‘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) Gluons couple to the color of a particle.
Careful: this is not the same as color in common language!
Two kind of hadrons (‘quark atoms’) exist:
Quark + Antiquark = Meson(e.g. pions)
3 Quarks = Baryon(e.g. proton, neutron) +
p 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 (SM) describes all these particles and 3 of 4 forces. We have confirmed the existence of those in the laboratory experiments.
The Standard Model
+ 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
Particles and Forces 13
The Higgs BosonOne 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
As a consequence, there should also be a spin-0 boson, the Higgs boson.It has not been found yet.
Similar to thecelebrity effect in a crowd.
Credit: CERN
Physi
cs
H
Part
icle
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
r
GMv
r
rGMv
)(
3
3
4~)( rrM
)(~ rrv
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
"spherical bastards”
Walter Baade 1893-1960
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 helium nuclei; the rest of protons
remain as hydrogen nuclei
Almost no elements heavier
than helium are produced.
25% of mass in helium 75% in hydrogen
No stable nuclei with 5 and 8 protons
The Nature of Dark MatterCan 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!