From Electrons to Quarks - 2 l The Standard Model l …And Beyond.

From Electrons to Quarks - 2

The Standard Model

…And Beyond

Electron – 1897

J.J Thomson

Top quark1995

A Century of Particle Physics

… And The Particle Zoo!

±, 0, e, ±,K±, K0

S, K0L,

0, p, n, +, 0, , , …

u u u d d d e

b b b

c c c s s s

g g g g g g g g

Z W+

e

Quarks Leptons+2/3 -1/3 -1 0

I

II

III

Boso

ns

Ferm

ions

The Standard Model

H

t t t

W-

The Standard Model

d u

d

NeutronProton

u d

u

Delta++

u u

u

The Electromagnetic Force

1 22

q qF k

r

q2

q1

Electron

Proton

Photon

n

Neutron

ne

Anti-electron neutrino

W-

The Weak Force

Radioactive decay ofthe neutron

e

Electron

Proton

p

The Strong Force

u

u d

d

g

Strong force caused bythe exchange of gluons

The Standard Model

SummaryAll known matter is of quarks and leptons that interact via one or more forces:

StrengthGravity 10-39

Weak 10-5

Electromagnetic 10-2

Strong 1

The Mass Puzzle

Imagine a room full of physicists

From L. Smith, Scientific American, July 2000

… and someone famous walks in…

… he attracts admirers, which makes it difficult for him to

move… …he has acquire

d inertia,that is,mass!!

Now imagine that it’s only a rumor that he is about to arrive…

… physicists cluster together to discuss the rumor…

… just as they did before, but

minus the famous person

Mr Higgs Boson

Professor Peter Higgs

…And Beyond

Fermilab

The Just-So Puzzle

Particle Mass [MeV]

electron

0.51

muon 105.65

tau 1776.99

u 2.25

d 5.00

s 95 .00

c 1250 .00

b 4200 .00

t 170,900 .00

Why is the neutronheavier than the proton?

Nucleon Mass [MeV]__________________N (u d d) 939.6

P (d u u) 938.3__________________

1.3 MeV

The Vacuum Energy Puzzle

The Standard Model predicts the energy density of the vacuum is > 102 GeV/fm3

According to observation, the energy density of the vacuum is < 10-52 GeV/fm3

Oops!

The Gravity Puzzle

10-39

Why is gravity so weak?

Nature’s Big Clue

The Fundamental Parameters of Natureh Planck’s constantc Speed of light in vacuumG Newton’s gravitational constant

llpp ~ 4 x 10 ~ 4 x 10-35-35 m m The Planck Length

3P

hGl

c

Brane Worlds

Our 3-dimensional world could be embedded within a higher dimensional space

Perhaps ours is but one of numerous brane worlds

2008 2008 The Era of the LHCThe Era of the LHC

Graviton

pp

Our world