We provide 3 slides, not for students, to separate the activities.

1. Rolling for Rutherford

Classroom PPT

It Starts with a Model.

The search for the building blocks of matter

New models came from experiments that used cutting-edge technology to change our view.

Aristotle and Democritus 400 BCE

Dalton 1803 AD

Mendeleev 1869

Thompson 1897

Rutherford 1910

Rutherford's Beam

Observations yielded many models for the world of the very small.

Ernest Rutherford(1871-1937)

• The team fired a beam of alpha particles at thin gold foil.• The beam particles then hit a screen and flashed.• Observers recorded the location of the flashes.

Rutherford's Beam

One experiment radically changed the existing models.

Existing models suggested that the electric charges in the atom were evenly spread out. The beam should pass right through—or deviate very slightly.

Rutherford's Beam

Most beam particles went straight through, and some were deflected.However, a very, very few reflected straight back to the source!

“It was quite the most incredible event that has ever happened to me. It was . . . as if you had fired a fifteen inch shell at a piece

of tissue paper and it came back and hit you.”

Rutherford's Beam

In our experiment, some marbles went straight through; others veered because of a collision. The number of collisions depends on how much of the target space is filled.

These data show that it's very unlikely to get zero hits—or seven. It's most likely to get three hits.

What would happen if there were more target marbles inside the apparatus? What if the marbles were smaller?

Rutherford's Beam

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Rutherford model:

• Negative electrons around a small, dense, positive center• Most beam particles deflected a little or not at all• A few beam particles deflected a lot

Competition of ideas

Rutherford's beam revealed structure. Today's beams collide and convert kinetic energy to mass—in the form of new particles. These beams reveal new particles.

Which particles get created is determined by simple rules of conservation. Emmy Noether noted that systems that exhibit mathematical symmetry also conserve certain quantities. You already know some of these: charge, mass and energy.

We'll explore more of these conservation rules in the next two days.

Emmy Noether(1882-1935)

Rutherford's Beam

2. Quark Workbench

Conservation Rules!

Emmy Noether worked out ways to predict preserved quantities in physical systems that obey certain mathematical symmetries.

Physical processes must retain (conserve) these quantities. You are familiar with some of these: chemical reactions conserve mass; falling objects conserve energy.

Today's activity exposes several more classification rules and hints at some new conservation rules.

Emmy Noether(1882-1935)

This chart shows a list of particles that are currently thought to be fundamental. It is divided into three classes:• Quarks• Leptons• Force CarriersThe quarks and leptons are further divided into three generations.

The table does not explain a number of critical underlying features of the particles and forces.

Use the puzzle pieces to create particles and determine the set of rules that allows their formation.

Conservation Rules!

3. Top Quark Mass

E = mc2

We said that the kinetic energy of the beam can turn into particle mass. You've seen a way to write this down:

Particles

Einstein: “The energy and mass of a particle are interchangeable.”

Noether: “And they are conserved.”

Beam energy becomes mass. That mass can be released as energy if the particle decays.

E = mc2

So particle beams have come full circle. Rutherford used one to probe atomic structure. Now we use them to create new particles and deduce their structure by watching them decay.

Particles

Today's activity does just that. We have data from a Fermilab experiment that produced the first top quarks (besides those that naturally occur). The experiments never saw the quark—only its decay products.

Particles

The detector can't see everything in the cartoon. We must use conservation rules to decipher what might have happened.

The opposing, colliding beam of protons and anti-protons provide the energy needed to make a top-antitop pair. These both decay very, very promptly.

Particles

Here is a picture of what you would see if able to look along the beam towards the middle of the detector.

Start with what you know about conservation and build enough information to decipher what we didn't see. That's the most interesting piece to this puzzle.

Particles in a cylinder

Get a D-Zero collision event from your teacher and try your hand at event reconstruction.

Particles

Ms. Noether gave us the tools to uncover many more conservation laws. We'll use some more of them on masterclass day to decipher what we didn't see in those events.