Probing the highest momentum protons in the nucleus

1
Probing the highest momentum protons in the
nucleus
John Arrington ? Argonne National Laboratory
Jefferson Lab, Newport News, VA
Electrons drive the chemistry of atoms, but
nuclei are at the core of matter
We need to understand the distribution of the
ultra-fast nucleons (protons and neutrons) in
nuclei These protons are associated with the most
violent interactions in nuclei, and are
especially sensitive to the effect of the nucleus
on the internal structure of the proton
gt 99.9 of the mass lt 1 trillionth
of the volume
We shoot a high energy electron beam from
Jefferson Lab at nuclei and look for electrons
that strike a single proton Those that strike
ultra-fast protons are easy to identify because
they have a higher energy
A nucleus is not a
simple, stationary collections
of protons and neutrons Nuclei represent
extremely active and violent environments
Similar to the difference between bouncing a
ping-pong ball off of a moving car and a
stationary car
Typical momenta are less then 200 MeV/c. These
measurements are designed to probe to 1000 MeV/c
Hall C at Jefferson Lab

• Incredibly energetic
• Highest energy protons moving at more than half
  the speed of light
• Even slow protons must change directions a
  billion times every trillionth of a second or
  they would escape
• The interactions of these ultra-fast protons can
  be used to shake loose information on the
  quarks inside

Short Orbit Spectrometer
High Momentum Spectrometer

• Measurements at Jefferson Lab have mapped out the
  number of ultra-fast protons in heavy nuclei.
  Follow-up measurements that finished in 2004
  will
• Probe even higher momentum protons
• Study light nuclei separate high-momentum
  protons coming from hard two-proton interactions
  and those that involve collective configurations
  of many protons

• Incredibly dense
• Nearly as dense as a neutron star
• If the moon were as dense, it would be smaller
  than the Washington monument

JLab 12 GeV upgrade Probe the quark
sub-structure of these energetic, high-density
configurations to look for exotic states of
matter formed by the strong interaction of
protons in the environment of the nucleus