people are strange or quarks, glue, and electrons, too: that’s what little boys and girls are made...
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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