The Squishiness of the Proton
Thomas Jefferson National Accelerator Facility
Hall-A Collaboration Experiment 93-050
Data Taking March 12 - April 13, 1998
Visit our web page at hallaweb.jlab.org/experiment/E93-050/vcs.html
Squishiness = How hard do we have to squeeze something to change its shape or size.
Squeeze
box with mouse
How do we squeeze a proton?
By pulling on it with electric and magnetic forces.
(This is the same way you squeeze
something with your fingers)
What are the
strongest electric forces we can produce in the laboratory?
|
Static electricity |
E=106 Volt/meter |
|
Use Electromagnetic Waves: |
|
|
Radio-Frequency (TJNAF): |
E=107 V/m |
|
Lasers: |
E=1012 V/m |
|
Gamma-rays |
E=1017 V/m |
|
High energy electron 10-15 m away |
E=1021 V/m |
The electric field from this electron shifts the mass of the proton by 1 part in a million.
How do we detect a momentary shift of 1 part per million in the proton mass?
Virtual Compton Scattering: Hit the proton, then take a picture.
The electromagnetic force from a high energy electron passing by a proton acts like a mallet hitting a chime. the proton and all its internal constituents (quarks, gluons, pions...) start to ring (oscillate).
An oscillating electric charge always radiates light at the frequency of vibration. The intensity of the light is porportional to the square of the amplitude of the oscillation.
The intensity of the light
radiated by the proton after it is shaken by the passing electron is
proportional
to the disturbance of the proton
by the passing electron.
This is the squishiness of the proton.
How to gently squish a proton, in 6 [not so] easy steps.
1) Prepare a beam of electrons, each with energy 10,000 times greater
than the rest mass energy of the electron.
General View of TJNAF
Accelerator Site
The Accelerating
Cavities
How Does the
Accelerator work?
2) Put lots of protons in front of each electron. At 700 Watts, the Hall-A target is the world's highest power liquid hydrogen target.
Installation of
Cryotarget, Aug. 1997
Close-up of
"Beer-can" target cells
3) Collide individual electrons in beam with individual protons in target. Only one electron in 100 billion in the beam hits a proton hard enough to ricochet the electron into our detector.
4) Detect scattered electrons. This determines the number of protons hit and how hard each proton was hit.
General view of Hall-A Spectrometers
5) Detect recoil protons.
6) Use Conservation of energy and momentum to measure the mass of everything left over. After the proton is hit by the electron, it can either radiate a high energy gamma-ray or break up into a proton plus other sub-atomic particles. The intensity of the peak around zero tells us the squishiness of the proton. The peak near 20,000 are events that broke the proton apart.
Observed events vs. "Missing Mass Squared"
Who built the equipment, conceived the experiment, carried out the measurements, and will analyse the results?
TJNAF Experiment
93050 Virtual
Compton Scattering Collaboration &
TJNAF Hall-A
Collaboration
Why Physics?
The 19th century global economy was dominated by the practical and theoretical understanding of Thermodynamics: the science of heat & motion.
The 20th century economy has been dominated by Quantum Mechanics: the understanding of the wave nature of matter.
The 21st century economy will be dominated by the atomic manipulation of matter.
This page created by Charles Earl Hyde-Wright:
chyde’at’odu.edu
This material is based on work supported by the U.S. National Science
Foundation under grant 9603218 and
Department of Energy grant 96ER40960.
Any opinions, findings, and conclusions or recommendations expressed in this
material are those of the author(s) and do not necessarily reflect the views of
the National Science Foundation or the Department of Energy.
Last modified: Sunday, November 15, 2003, 12:10 MET DST