People are StrangeOR

Quarks, Glue, and Electrons, too:That’s What Little Boys and Girls Are Made Of!

Jeff Martin

University of Winnipeg

Jan. 25, 2006

Skywalk Lecture Series

A Couple of Big Questions

People have long asked:• What is the world made of?• What holds that stuff together?

Let’s pick some object and zoom in on it.

The Big Apple

courtesy NOVA (PBS.ORG)

• Note: one cannot see this with a normal microscrope.

a carbon atom

• protons and neutrons are inside

Humans have not yet determined how to “see” anything smaller than a quark.

0.000000000000000001 metres

The Standard Model

Ingredients in the Standard Model

A “Simple” Recipe:How to Make a Proton

u

u

d

Quark charge:

u +2/3 e u +2/3 e d -1/3 e---------------------

1 e

2 “up” quarks+ 1 “down” quarkmakes a proton.

However, we know it’s all more complicated than that…

u

u

d

Quarks are heldtogether in a bagby gluons (carriersof the strongforce)

gg

glue: bleccch. Not too tasty!

The Proton:The Disturbing Discovery

u

u

d

ss

Zooming in,we begin to seevirtual quarks.

In particular,STRANGE quarks

Proton uud + g + + + + …uu dd ss

The ‘‘Sea’’

Wow, it’s reallycomplicated!

And if you really zoom in…

Previous Data on Strange Quarks

70% regular stuff(up and down quarks)

30% strange quarks!!!!

About 50 pounds of me is strange!

How do you measure something like that?

• Do an experiment:– Fire electrons at a proton target and look

at the way that they scatter from it.

– That’s the way the atomic nucleus was discovered! (Rutherford, 1911)

• And how does that tell you about strange quarks?– It doesn’t: you actually have to measure

using the weak force and compare to “regular” experiments.

The Experiment

target

In our experiment, the electron is moving at 99.999999% the speed of light.

Note: University of Winnipeg does not have a gigantic electron accelerator.

Ever wonder what physics professors

do on their summer

“vacation”?

A Particle Physics Experiment:“Gee-Zero”

CaltechCarnegie-MellonWilliam+Mary

Grinnell CollegeHampton

IPN-OrsayISN-Grenoble

KentuckyLaTechNMSUJLab

TRIUMFUConn

U IllinoisU ManitobaU Maryland

U MassUNBC

VPIYerevan

and theUniversity of Winnipeg

Jefferson Lab, Newport News, VA, USA

superconducting magnet

detectors (Ferris wheel)

target (some protons)

G0 Experiment

electrons

The Question

• How much of the proton’s magnetism comes from strange quarks?

The Answer (from G0)• About 5%• And by the way: that is AMAZING!

– (way bigger than one would naively expect)

Strange Quarks and the Economy

• “The results, reported in this week's Physical Review Letters, showed that this was far greater than had been predicted. In particular, some 5% of a proton's magnetism is contributed not by the host quarks but by visiting strange quarks that have popped out of nowhere.”

• “So, next time you have an MRI scan, remember that part of the picture depends on something that isn't really there. Strange, eh?”

A Strange New World

• We now know that strange quarks play a bigger role in the properties of the proton than anyone ever thought was possible!

• Still more work to do… this summer.

My website:nuclear.uwinnipeg.ca

Other resources:particleadventure.orgwww.pbs.org/wgbh/nova/elegant

This work is funded by:Natural Sciences and Engineering Research Council of Canada