Particle Physics at CCP
Japanese version is here.
PARTICLE PHYSICS
Particle physics, or high energy physics,
aims to understand the fundamental
constituents of matter and their interactions.
Ordinary matter surrounding us is made of atoms such as Oxigen and Carbon,
whose size ranges from about 10-10 to 10-12 m.
An atom consists of a nucleus at the center and electrons flying around it.
An atomic nucleus is further made of hadrons such as the proton, neutron
and pion (about 10-15 m).
However, this is not the end of the story.
According to the results from high energy accelerator experiments
performed over the last few decades,
hadrons are made of more fundamental particles, the quarks,
which are smaller than 10-18 m.
The basic language of particle physics to describe particles and
interactions among them is quantum field theory,
i.e., relativistic quantum mechanics of particles
which are represented in terms of fields extended in space-time.
At low temperatures, quarks are confined inside hadrons by a force
called the strong interaction.
The fundamental theory of this force is given by a quantum field
theory called QCD (Quantum Chromodynamics), according to which
the strong interation is provided by the exchange of gluons among quarks.
While QCD successfully explains many properties of hadrons observed in
accelerator experiments at high energies,
the fundamental properties of hadrons at low energies
such as mass spectrum and decay probabilities have remained
unexplained due to the strong-coupling nature of QCD in the
low energy region.
LATTICE FIELD THEORY
During the past decade Monte Carlo numerical
simulation techniques have become an important tool in the study of
field theories,
especially for strong-coupling, or non-perturbative, phenomena,
such as those governing the low-energy properties of hadrons in QCD.
For these phenomena
the present analytical methods are often insufficient.
Numerical simulations of field theories are carried out using a
formulation on a space-time lattice called lattice field theory.
Particle physics research at the Center aims to significantly advance the
study of lattice field theories by exploiting the
computing power provided by the CP-PACS computer.
LATTICE
QCD
A major subject in this area is lattice QCD.
A long-standing problem in lattice QCD is a precise understanding of the
properties of light hadrons.
The development of the computer power devoted to QCD calculations of
hadrom masses by major research groups is summarized in a figure
[JPEG |
GIF |
PDF].
The CP-PACS enabled a calculation which is one to two orders of magnitude
larger than previous studies.
Another important problem is the elucidation of the nature of the
finite-temperature phase transition separating the low-temperature
hadron phase from the high-temperature quark-gluon-plasma phase.
Clarifying the properties of hadrons containing heavy quarks, such as charm
and bottom, is also very important for the phenomenology of weak interactions.
Computational research at the Center addresses these issues in
detail.
A brief overview of the QCD results from the CP-PACS, obtained so far,
is given below:
Numerical simulation techniques are also
important for other problems of the standard model of fundamental particles,
e.g., the question of generation of baryon number asymmetry
through the electroweak transition expected in the early Universe,
and the problem of chiral fermions and chiral gauge theories.
The method is also applicable
to unconventional types of field theories such as the dynamical triangulation
formulation for quantum gravity. Research at the Center is expanding
in these areas as well.
LIST OF PUBLICATIONS
