From Quarks to the Cosmos!

  Prof. Richard E. Hughes  3046 Physics Research Building, 614-688-5690   Email: [email protected]

Course Web Address:  http://www.physics.ohio-state.edu/~hughes/freshman_seminar/ Course goals:  Particle physics and astronomy have seen incredible gains over the past twenty years. And yet, though  particle physics concerns the very small    astronomy concerns the extremely large,  it is clear that these two disciplines are very closely related. This course will introduce the non-expert to these most exciting sciences, and describe the major research aims of each. We will focus on important questions at the intersection of physics and astronomy that have some hope of being answered over the next decade.

Richard E. Hughes Lecture 1; p.1

Course Structure

    Class meets once per week Each class will focus on one major research area in particle physics/particle astrophysics  Many of these but not all have some participation by OSU physicists Each class will be organized like a “Press Conference”    Except this one!

YOU are the press: After each class, writeup a ~two paragraph summary of the press conference  Like you might expect to see in your local paper  This should be easy: expect it should take you about 30 minutes outside of class  Prior to / after class: explore topics on web Today’s class: brief introduction to particle physics and the important questions physicists are trying to answer

Richard E. Hughes Lecture 1; p.2

What is particle physics?

 Particle physics addresses some of the most fundamental questions that people have been pondering for centuries:    What are the building blocks of matter? Why are these blocks what they are? Can we explain their properties, such as mass? How do they interact?  In a way, particle physics is complementary to cosmology:  cosmology studies the largest possible objects (such as galaxies, with hundreds of billions of stars!), and particle physics studies the smallest possible objects imaginable.

Richard E. Hughes Lecture 1; p.3

Build this…

Building Blocks of Man

…or build this!

Richard E. Hughes Lecture 1; p.4

Distance Scales

               Football Field 109m Person: ~1.7m

Hand: ~15cm Mosquito: ~2cm Ant 5mm Human hair: 100microns Human red blood cell, bacterium:10microns HIV virus: 100nm Diameter of DNA: 2nm Width of Protein: 0.5nm

Radius of Hydrogen: 25pm Size of the atomic nucleus: 10fm Size of proton: 1fm Size of quarks: <10^-18m Planck Length: 10^-35m distances below this make no sense!

Richard E. Hughes Lecture 1; p.5

What is a building block?

 What is the most elementary building block of matter? First, we need to define elementary:  Let us define an elementary particle as something that  has no discernable internal structure;  appears “pointlike”. (At least in current experiments…) • First, people thought that the

atom

was elementary: The atom, as it was envisioned around 1900 - a ball with electrical charges inside, bouncing around!

Richard E. Hughes Lecture 1; p.6

Rutherford Scattering Experiment

a Rutherford Experiment gold foil Hard central core!

Like firing a cannon ball at a paper towel and having the ball bounce back Most of the atom is empty space.

The alpha particle is probing the structure of the gold in the foil. This basic idea has been repeated many times over the last hundred years to further probe the structure of matter.

Richard E. Hughes Lecture 1; p.7

The atom has a rich structure!

 Eventually, it was realized that the atom is not elementary:  it consists of a positively charged

nucleus

and negatively charged

electrons.

 The properties of outermost electrons in atoms give rise to chemistry and biochemistry, with all of its complexity!

 The

electron

, as far as we know, is elementary!

Richard E. Hughes nucleus electron

If the nucleus were as big as a baseball, then the entire atom's diameter would be greater than the length of thirty football fields!

Lecture 1; p.8

Is the nucleus elementary, too?

   Unlike the electron, the nucleus is not structureless! It consists of

protons

and

neutrons.

But protons and neutrons are not elementary, either!

They consist of elementary.

quarks

, which to the best of our knowledge are

nucleus

Experiment in 1960’s High Energy Electrons

Richard E. Hughes neutron proton Lecture 1; p.9

Break down H

2

0

H O H 

p



e



u d



Richard E. Hughes

p

28

u

8

p

 8

n

 8

e

 8 

p

 26

d n



p



e

  10

e



p

Lecture 1; p.10

Break down Pb

Pb



Richard E. Hughes

82 

p

289

u

 125   332

d n

 82 

e

  82

e



Lecture 1; p.11

H

2

0 vs Pb

H

2

O

 28

u

 26

d

 10

e



Pb

 289

u

 332

d

 82

e

 The sizes of the piles are different, but ratio of u/d is not all that different and e/u ratio is not all that different. Looking at H 2 O and Pb this way…they don’t look all that different.

Richard E. Hughes Lecture 1; p.12

The Standard Model

  The most comprehensive theory developed so far that explains what the matter is made out of and what holds it together is called the

Standard Model

.

In the Standard Model, the elementary particles are: 

6 quarks

(which come in three sets) 

6 leptons

(which also come in three sets)  Why do quarks and leptons come in sets (which are called generations)? Why are there three of them?

We don't know.

 Note that the Standard Model is still a model because it's really only a theory with predictions that need to be tested by experiment!

 Going to very high energies the theory begins to breakdown. (Effective Theory)

Richard E. Hughes Lecture 1; p.13

How many quarks?



Quarks:

They are fundamental particles…make up protons and neutrons…but other exotic forms of matter as well. First proposed in 1960’s.

There are 6 quarks, and they come in pairs:

u

p

c

harm

t

op/

t

ruth 1995 1974

d

own

s

trange 1978

b

eauty/

b

ottom

Richard E. Hughes Lecture 1; p.14

What about the electron?

  We said earlier that apart from the six quarks, the electron was also elementary. It turns out that the electron is not alone -- it belongs to a group of six particles called

leptons

! Just like quarks, leptons come in pairs:

Electron neutrino

n

e Muon neutrino

n m

Tau neutrino

n t

e electron

m

(mass = 205 x mass of e) muon

t

(mass = 3503 x mass of e) tau Richard E. Hughes Lecture 1; p.15

What are neutrinos?

 W. Pauli postulated their existence in order to save the energy conservation principle in certain types of radioactive decays, known as beta-decays: n  p 

e

 n

neutron decays into proton plus electron plus neutrino

 E. Fermi called them "neutrinos" -- "little neutrons" in Italian.

 Neutrinos hardly interact with anything at all. In fact, the earth receives more than 40 billion neutrinos per second per cm 2 . Most of them just pass through the earth, as if it's not even there!

Richard E. Hughes Lecture 1; p.16

What particles are important?

Everything you can look at contains the simple protons neutrons, and electrons.

  So the natural expectation is that protons, neutrons, and electrons are There are about:  0.5 protons per cubic meter of universe 330 million neutrinos per cubic meter One billion photons per cubic meter

Richard E. Hughes Lecture 1; p.17

  

Antimatter!

The quarks and leptons discussed so far make up “ordinary” matter.

For every one of these there is an antimatter counterpart.

  Antiup quark, Antidown quark, etc.

antielectron (positron), antielectron neutrino, etc.

Antihydrogen: 

e

Matter Antimatter

u d p

Never shake hands with your antiself!

An oddity: as far as we can tell, all of the luminous material we see in the universe is MATTER not ANTI-MATTER!

The predominance of matter over antimatter in the Universe is one of the biggest mysteries of modern high energy physics and cosmology!

Richard E. Hughes Lecture 1; p.18

What holds everything together?

  Things are not falling apart because fundamental particles

interact

with each other. An interaction is an

exchange

of something.

A rough analogy of an interaction: the two tennis players exchange a ball ?

But what is it that particles exchange? There is no choice - it has to be some other special type of particles! They are called

force particles (Intermediate Vector Bosons)

.

Richard E. Hughes Lecture 1; p.19

Four fundamental interactions

 There are four fundamental interactions between particles:

Interaction Strong Mediating particle Gluon (g) Electromagnetic Photon (

g

) Who feels this force Quarks and gluons Everything electrically charged Weak Gravity W and Z Graviton (?) Quarks, leptons, photons, W, Z Everything!

Richard E. Hughes Lecture 1; p.20

The strong interaction

 The

strong

force holds together quarks in neutrons and protons.

 It's so strong, it's as if the quarks are super-glued to each other! So the mediating particles are called

gluons

.

 This force is unusual in that it becomes stronger as you try to pull quarks apart.

 Eventually, new quark pairs are produced, but no single quarks. That's called

quark confinement

.

Richard E. Hughes Lecture 1; p.21

The electromagnetic interaction

 The residual

electromagnetic

interaction is what's holding atoms together in molecules.

 The mediating particle of the electromagnetic interaction is the

photon

.  Visible light, x-rays, radio waves are all examples of photon fields of different energies.

Richard E. Hughes Lecture 1; p.22

The weak interaction



Weak

weak:  interactions are indeed Neutrinos can only interact with matter via weak interactions -- and so they can go through a light year of lead without experiencing one interaction!

  Weak interactions are also responsible for the decay of the heavier quarks and leptons.

So the Universe appears to be made out of the lightest quarks (u and d), the least-massive charged lepton (electron), and neutrinos.

Richard E. Hughes

n m

Lecture 1; p.23

Gravity

 The Standard Model does not include gravity because no one knows how to do it.

 That's ok because the effects of gravity are tiny comparing to those from strong, electomagnetic, and weak interactions.

 People have speculated that the mediating particle of gravitational interactions is the

graviton

-- but it has not yet been observed.

Richard E. Hughes Lecture 1; p.24

Seething Underworld

 Lots of gluons, photons, even strange and charm quarks inside protons and neutrons.

g

e

 g

u c e



p c g u d g

g

e



d g g u d n

Richard E. Hughes Lecture 1; p.25

The Big Questions

      How was matter formed at the beginning of the universe?

How does it stay together?

What are the fundamental building blocks of nature?

What are the basic laws upon which the universe operates?

Astrophysicists have found that less than 5 percent of the mass of the entire universe consists of the kind of "luminous" matter that we can see. What is the dark matter that makes up the rest of the universe? Why is our universe is made of matter, while antimatter has all but disappeared?

Richard E. Hughes Lecture 1; p.26

Fermi National Accelerator Laboratory

Proton-antiproton collider: Question: What are the fundamental building blocks of nature?

Only place in the world where top quarks can be made

Richard E. Hughes Lecture 1; p.27

Gamma-ray Large Area Space Telescope

Gamma Ray Bursts: Power at maximum up to 1,000,000,000,000,000,000 (quintillion) times the Sun's power

Richard E. Hughes

Matter that radiates across the entire electromagnetic spectrum is only 10% of the total mass of the universe: 90% of the mass of the universe does not emit light at any wavelength. Can detect this so called dark matter by its gravitational effects on luminous matter Compton Observatory all sky gamma-ray image of the unidentified sources (active galactic nuclei, pulsars, supernova remnants, dense molecular clouds, and stellar-mass black holes within our Galaxy?)

Lecture 1; p.28

Richard E. Hughes

ATLAS

Proton-proton collider increase energy by factor of 7 over Fermi Tevatron!

Main purpose: Search for a special particle – - the Higgs – that gives all other particles MASS!

Lecture 1; p.29

NUMI/MINOS

Idea: make neutrinoes, shoot them underground approximately 450 miles to Minnesota; study neutrino mass

Richard E. Hughes Lecture 1; p.30

Supernova / Acceleration Probe

Studying the Dark Energy of the Universe

A star's distance can be estimated from its brightness as seen on Earth, if its total emitted light is known — the farther away it is, the dimmer it appears. Accurate estimates of total emitted light are possible for only a few kinds of astronomical objects such as type Ia supernovae most distant supernovae are dimmer than they would be if the universe were slowing under the influence of gravity; they must be located farther away than would be expected – the conclusion is: the Universe is expanding!

some form of dark energy does indeed appear to dominate the total mass-energy content of the Universe, and its weird repulsive gravity is pulling the Universe apart

Richard E. Hughes Lecture 1; p.31