Transcript Nuclear Physics - University of Houston

What’s New in Nu-clear Physics
Ed V Hungerford
University of Houston
According to Pogo:
“Nuclear Physics is not
so new, and not so clear
either.”
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The Answers to our questions are
only as good as the questions
themselves
Why did the tree grow in the
notch in the fence ?
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75 years ago Nuclear Physics was New
•The neutron had just been discovered
•The Proton and Neutron were considered elementary particles
•The nuclear force was not understood
•Nuclear models were primitive and based on classical
liquids
Today Nuclear Physics in some sense is Mature
•Nucleons are not “elementary” but are composed of other
particles called quarks
•The nuclear force is understood as an exchange of field quanta
called gluons
•The nucleus is a VERY complicated interaction of many hadrons
whose interaction is described by a theory called Quantum
Chromodynamics
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The Particles and Symmetries of the
Standard Model
3
Families
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There are 4 known interactions in nature
•One of the fundamental driving philosophies of physics is the
assumption that these interactions can be “unified”
•Two of these are manifestations of the same force (electroweak)
•QCD is patterned after the electroweak interaction (gauge theory)
•Gravity still lies outside a quantum theory
•The new discovery of Dark Energy, if it is real, may imply a 5th force
Field
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QCD
The Interaction through Fields
Particle A
Particle B
A Field Quanta
The interaction of B with
A occurs through the
absorption of field quanta
at B produced by A
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QCD Features
• An interaction that becomes stronger the greater
the distance and the lower the energy between interacting
particles
• A weak interaction at short distances and high energies
• A permanently bound quarks and gluons
• A self interaction between the field quanta (gluons)
• A highly non-linear theory greatly complicating
calculations and making intuitive predictions difficult
• A symmetry of SU(3) expressed by 3 states of quarks
and Gluons (color)
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The Quark and Gluon Constituents of the Baryon
Valence Quarks
Gluon Field
Sea Quarks
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Quantum ChromoDynamics (QCD) is the
Theory of the Strong Interaction
(Nuclear Force)
Quarks and
Gluons
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Flux Tube
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Linear Potential vs
distance
How do we probe a Nucleon or a Nucleus
To determine its Quark Content ?
Incident
Hadron
Incident
Electron
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Quark Scattering
Emission of a Quark Stretches
the “interaction String”
When the string breaks, Quarkanti-quark pairs are produced
This is called Hadronization of
a Quark Jet
Long Range Nuclear force
Collapses to quark-antiquark
Exchange (Yukawa Interaction)
the “interaction String”
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Chiral Symmetry, and Mass
Chiral symmetry is the fundamental symmetry of QCD
Velocity
Right Handed
Velocity
Left Handed
But the particle must not have mass
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The QCD Condensate
Particles acquire mass through their interaction with the vacuum, i.e.
the condensate of quarks and gluons in the vacuum
A nucleon in a simple visualization, is a bubble in the vacuum
condensate
Interaction of these quarks with the condensate at the bubble surface
gives an “effective” mass to the system.
Chiral Symmetry is then said to be spontaneously broken
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The Vacuum is NOT Empty
This Computer simulation
shows the instantaneous
gluon field that might be
Present in a vacuum. Red
Indicates bending
(winding) in the field lines
perhaps a precursor to quark
condensates
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Each of the 4 interactions is has its own
impact on the existence of our Universe
The Strong (nuclear) force is responsible for the creation
and stability nuclear matter
Phase Diagram of Matter
We Live Here
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Studying the Vacuum and QCD
Relativistic
Colliding
Nuclei
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Quark Gluon
plasma
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Hadronization
Connecting the very large to the very small
One of the more recent advances
in physics has been to connect
microscopic theory to macroscopic
(cosmology)
For example, stellar burning and
supernovae produce the nuclei of
which the Universe is composed
We can use this information to
look back in time, as well as discuss
the present features in our
universe
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Mesons and baryons are
composed of quarks
Flavor SU(3) Symmetry
Allows Placement of lowest Mesons
And Baryons in Symmetry Octets
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The Nuclear Equation of State
Nuclear Matter
Neutron Star
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A modern cut-away view of a Neutron Star
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Measuring Matter Creation in the Galaxy
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Proton number vs Neutron Number Stability
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The Present Model of a Supernovae
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Inside a Supernova
Extreme temp: photodissociates nuclei
back to protons, neutrons and alphas.
>8 M evolves ~107 yr
3000 km
Core
bounces
3x107 km
Huge thermal
emission of
neutrinos
~5-10 seconds
Neutronisation: p+e-  n+ne
n
n
n
10 km
n
n*
n
n
.
M
n
100 km
Dense
core
n
n
.
M
n
e++e-  g+g ; g+g  nx + nx (all flavours equally)
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r ~ few x rnuclear
Supernovae: Facts and Figures

Energy release ~3x1046 J (the
gravitational binding energy of the
core), in about 10 seconds






Equivalent to 1000 times the energy
emitted by the Sun in its entire
lifetime.
Energy density of the core is
equivalent to 1MT TNT per cubic
micron.
99% of energy released is in the
form of neutrinos
~1% is in the KE of the exploding
matter
~0.01% is in light – and that’s
enough to make it as bright as an
entire galaxy.
Probably site of the r-process.
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¼ MT test
(Dominic Truckee, 1962)
A Computer model of a Supernovae
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A Brief Summary
Nuclear Science has tremendous breadth and complexity
After 75 years we have found some to the “right” questions to ask but
others remain
I have purposely avoided discussion of the more traditional nuclear studies
There are impressive new results and insights into nuclear matter. But these
require detailed exposition and are difficult to develop to grasp without some
prior knowledge.
As a mature, advanced science, there are significant applications in
Including the fields of Medicine, Computing, Industrial Products, Energy,
Finance, etc.
More than 50% of the Phd graduates in Nuclear Physics are employed
in industry, medicine, and national defense.
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06-20,2005
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