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!