Deep Inelastic Scattering and

its Impact on Quark Models

Saptaparnee Chaudhuri

Department of Physics and

Astronomy

Nobel Prize in Physics in 1990

Jerome I. Friedman Henry W. Kendall Richard E. Taylor

2

Scattering can determine structure:

Rutherford’s great legacy

Rn (alpha particle

source)

Alpha particle

Zinc sulphide screen

Microscope

Gold foil

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Atomic Nucleus Discovered in 1911

Protons Discovered in 1919

Neutron Discovered in 1932

In late 1950’s the protons RMS radius was found to be about 10-13

cm.

Are they Fundamental particles? 4

1964 Gell-Mann & Zweig proposed that protons and

neutrons and other particles are composed of spin ½

constituents- QUARKS

3 types

UP, DOWN, STRANGE

they have fractional charges UP(+2/3) DOWN(-1/3) STRANGE(-1/3)

Proton(u,u,d) Neutron(d,d,u)

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Are Quarks Real?

Many Unsuccessful Searches

-Accelerators, Cosmic Rays, Terrestrial Environment, Sea Water,

Meteorites, Air etc.

Fractional Charges

-Considered by many to be unreasonable

General Point of View In 1966

Quarks are most likely just mathematical representations

Useful but NOT real!

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Stanford Linear Accelerator Completed in 1966

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The SLAC-MIT Experiment

Linear Accelerator (SLAC) provided

20 Billion electron-volt electrons

Effective Magnification was 60 Billion times greater than

ordinary light

(Effective Magnification is proportional to Energy)

Examined the insides of the protons and neutrons

PROVIDED THE FIRST DIRECT

EVIDENCE FOR QUARKS

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SLAC Magnetic Spectrometers

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Picture reference” Rutherford’s legacy in particle physics:Exploring

the proton” 10

The Experiment(continued)

Deep Inelastic electron-proton scattering

e + p e + Many Particles

Electron

p

p'

Proton

P=(M,0)

Hadrons

P’

q = p-p’

Momentum transfer

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Nuclear Form Factor

f(x) is the charge

function

q = p – p’

Results suggested that protons has “point-like” constituents

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|F(q2 ) |2

Probing particle

Object

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References. Particles and nuclei by Povh. Rith. Zetsche Rutherford’s legacy in Physics:Exploring the proton