Download The Many Facets of Quantum Chromo Dynamics

Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
The Many Facets of
Quantum Chromo Dynamics
Thomas Mannel
Theoretische Physik I
Universität Siegen
Public Lecture, Part II, Oct 8th , 2012
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Contents
1
Peculiar properties of QCD
2
Some of the facets of QCD
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
3
Summary: (Future) QCD Machines
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Peculiar Properties of QCD
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Peculiarities I: Running Coupling
For massless quarks:
QCD does not have any intrinsic length scale
(remember:
[mass]=[Energy]=[Temperature]=[lenght]−1 =[time]−1 )
This is in fact the same for Maxwell’s theory of
electromagnetism
Consider the potential between two static quarks
(or static charges) at a distance r :
for dimensional resons:
α
V (r ) =
α : dimensionless constant
r
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
This is only true on Maxwell’s theory:
Coulomb Potential
By renormalization QCD generates a scale ΛQCD
(“Dimensional Transmutation” (Coleman))
ΛQCD r is dimensionless:
V (r ) =
1
α(ΛQCD r )
r
Concept of “running constants” in quantum theories
Usually the fourier transformed is studied 1/r → Q
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
In almost all quantum field theories the coupling
increases as the distance decreases
... except in a special class of field theories with
Asyptotic Freedom
α(ΛQCD r ) → 0
α(ΛQCD /Q) → 0
T. Mannel, Siegen University
as r → 0
as Q → ∞
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Peculiarities II: The States in QCD
QCD is the theory of quarks and gluons
Observation: There are no free quarks (and gluons)
QCD has the property of Confinement
This is compatible with a growing coupling as r → ∞
Numerical Simulations of QCD (“Lattice QCD”)
indicates a linear Potential between static quarks at
large distances:
V (r ) = σ · r
σ : String Tension
There are many states which can be built out of
3, 4 or 5 different types (“flavors”) of quarks
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Buliding Principle for the hadron states
The color of quarks:
The binding force is due to the “color charge”
The force is mediated by “gluons”
Allowed are only colorless states: Confinement
Bound states of a quark and an antiquark: Mesons
... and of three quarks: Baryons
The flavor of quarks
There are six flavors of quarks
Allows for a large “zoo” of hadrons
Except for top hadrons: The top
lives too short to form hadrons
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Lattice QCD predicts the masses of these states:
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Some of the Facets of QCD
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Quarks become Jets: Perturbative QCD
At large momentum transfers = shot distances
Approximation by perturbation theory
Use of “Feynman Diagrams”,
which also serve as an illustration:
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Quarks are confined in hadrons:
Must know the probability to find a quark in a hadron,
when it is probed with large momentum transfer Q
Red Blob: Non-perturbative, usually input from a
measurement.
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Qutgoing Quarks turn into “Jets”
Jet = bundle of Hadrons
Total momentum of the hadrons = momentum of the
initial quark
Probability that a quark turns into hadrons = 100%
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
T. Mannel, Siegen University
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
T. Mannel, Siegen University
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
T. Mannel, Siegen University
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Summary of perturbative QCD
QCD is well tested at short distances
... even at the quantum level
Nonperturbative input is well constrained
Precision measurement and tests possible
αs (Mz ) = 0.1184 ± 0.0007
T. Mannel, Siegen University
(PDG 2012)
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Processes of Hadrons
At long Distances the coupling becomes strong:
Perturbation Theory becomes useless!
What about “soft processes”
= processes which are sensitive to long distances?
Various possibilities:
Use quark models
Use approximate symmetries of QCD
Effective Field Theories
Use analytic properties of Quantum Field Theories:
QCD Sum rules
Tackle non-perturbative QCD numerically:
Lattice QCD simulations
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Effective Field Theories
Usually Effective Theories replace the Quarks and
Gluons by the the degrees of freedom which are
“relevant” at this scale.
Effective Theories are systematic expansion of QCD
High Energies (Q → ∞):
Quarks and Gluons are relevant
→ perturbative QCD, Expansion in 1/Q
Very slow hadrons (Q → 0):
Pions and Kaons are relevant
→ approximate symmetries, Expansion in Q
Heavy Quarks (mQ → ∞):
Light Quarks and Gluons are relevant
→ Use approximate symmetries, Expansion in 1/mQ
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
This machinery works very well:
Detailed understanding of pion-pion scattering at
small energies
Detailed understanding of pion-nucleon scattering at
small energies
Precision calculations for processes with heavy
quarks
However:
Predictions are often not in terms of αs and of ΛQCD
Predictions are often only relations between hadronic
quantities (symmetries)
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
QCD Sum Rules
Make use of the fact that all quarks eventually have to
turn into hadrons
Duality between quarks and hadrons
Dual description:
There are ways to project out the lowest states
Can be used to make reliable QCD based estimates
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
This machinery works also very well:
Estimates for static properties (masses ...)
Estimates for decay amplitudes of particles
... in particular for hadrons with heavy quarks
Predictions in terms of QCD parameters
However:
Limited precision
Uncertainties are hard to estimate
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Numerical Simulations: Lattice QCD
The only known nonperturbative approach from first
principles
Uses a discrete space-time grid for numerical
evaluations of QCD
Extensive and expensive Computers needed
Forschungszentrum Jülich Rechenzentrum TU München
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
This has become an almost separate field of research:
Calculation of static properties (masses ...)
Processes can be calculated, presently only for
special kinematics
Can be combined with effective theories and also
with perturbation theory
Predictions in terms of QCD parameters
However:
Limited by computing resources
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
Hot and Dense QCD
High temperatures also correspond to high energies
Does hadronic matter at high temperatures and high
pressures become Quark-and-Gluon matter?
Lattice simulations indicate a phase transition:
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Quarks become Jets: perturbative QCD
Quarks become Hadrons: Nonperturbative QCD
Hot and Dense QCD
The Phase Diagram of QCD
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Summary
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Summary
QCD will remain one of the hottest topics
in particle and hadron physics
As a complicated Quantum Field Theory it will remain
an attractive research subject for theorists
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
QCD Machines 0: Hera at DESY
H1
ZEUS
Inner Structure of the Proton
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
QCD Machines I: LHC
ATLAS
CMS
LHCb
Proton Proton Collisions, Higgs Search (Discovery?)
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Dedicated Heavy Ion experiment at LHC: ALICE
Hot and Dense QCD
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
QCD Machines II: GSI at Darmstadt
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
Heavy Ion Research, Nuclear Matter, Hot and Dense QCD
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
QCD Machines III: RHIC at Brookhaven
High Energy Heavy Ion Collisions
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
The Future QCD Machine: FAIR at GSI
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
The future Workhorse for QCD Studies ...
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
The final Outlook
QCD is a very rich theory with many facets:
It is an important part of what we call the “Standard
Model pf Particle Physics”
It has a rich phenomenology, such as the “chemistry
of the various nuclei”
It is important also for astrophysical objects:
Neutron Stars, Dwarf Stars, our own sun ...
QCD will be with us for many more years, not only as
a topic in fundamental research
T. Mannel, Siegen University
The many facets of QCD
Peculiar properties of QCD
Some of the facets of QCD
Summary: (Future) QCD Machines
The final Outlook
QCD is a very rich theory with many facets:
It is an important part of what we call the “Standard
Model pf Particle Physics”
It has a rich phenomenology, such as the “chemistry
of the various nuclei”
It is important also for astrophysical objects:
Neutron Stars, Dwarf Stars, our own sun ...
QCD will be with us for many more years, not only as
a topic in fundamental research
Thank You
T. Mannel, Siegen University
The many facets of QCD