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Research Programme
- Mission:
The programme is mainly directed at fundamental research in the field of
particle
physics. More specifically, our goals are to study properties and interaction
mechanisms of both hadron-hadron and e+e--collisions
and to confront the results obtained with the predictions and the parameters
of the models describing them.
- Scientific problem:
The most fundamental constituent particles known at present are the 6 quarks
and the 6 leptons. Except for possibly the 3 neutral leptons (the neutrinos),
these particles carry mass ranging from 0.5 MeV/c2 (electron,
discovered 1897) to almost 200 GeV/c2
(top-quark, discovered 1995).
The "lightest" quarks (called up and down) form protons and neutrons and
these, in turn, are the building blocks of atomic nuclei. The atomic shells
are filled by the lightest charged lepton (the electron).
The neutrino plays an
important role in, e.g., nuclear beta-decay and the power production in the
sun. Heavier quarks and leptons, in general, do not act as building blocks of
our present day matter, but play a vital role in the understanding of every
day matter and in theories for the early universe.
The forces acting between these fundamental matter particles (of half-integer
spin) are carried by field quanta (of spin 1). They are known as gamma
(photon) and W+, Z0, W- for the electroweak
force felt by leptons and
quarks, as well as g (gluons, 8 in total) for the strong force felt by quarks
alone. In addition, a spin 2 field particle (the graviton) is needed to carry
gravitation and a spin 0 particle (called Higgs) to explain the particle
property of mass.
- Objectives:
The objectives are to gain information on the properties of the most
fundamental building blocks of matter, the quarks and leptons and (still more
importantly) on their interactions via the field particles.
- Subject matter researched:
- Strong interactions (QCD)
Quarks do not exist as free particles in nature,
they are confined into so-called hadrons (protons, neutrons or pions, kaons,
etc.).
In that, a high energy hadron colliding with another is
considered a high energy beam of quarks colliding with another beam of quarks,
or even gluons inside the hadrons.
There is, however, a second way to study the more special case of an
interaction of a quark with its anti-quark. In a high energy collision between
an electron e- and a positron e+, these two particles
can annihilate into a virtual photon or a Z0, which can decay into
a pair of a quark and an anti-quark interacting with one another.
- Electroweak interactions
The electroweak force is transmitted by the exchange of photons,
W- and Z-bosons. Like gluons, the electroweak bosons interact among themselves.
For example, under certain circumstances,
neutral Z-bosons can decay into pairs of oppositely charged W-bosons.
The properties of and interactions between electroweak bosons give insight
in the fundamental interactions of matter.
- New particle searches
A mechanism to explain how particles acquire mass is available as theoretical
idea. The theory predicts a particle, called Higgs boson, with rather distinct
properties. So far this particle has not been observed.
More advanced theories that pose solutions to some of the outstanding
theoretical issues predict an even much larger set of elementary particles
than is presently observed.
By finding new particles with specific properties, these theories could be
affirmed and the valid solution could be singled out.
- Methods and anticipated results:
The L3 experiment is currently
accumulating collision data
using a multipurpose detector in the Large Electron Positron
(LEP) ring of CERN.
From 1989 until 1996 e+e- annihilation events at
energies near the Z0 mass have been recorded.
The study of the data of these Z0 is being completed.
The principle aim is a high precision test of the present Standard Model
of electroweak and strong interactions including a high precision measurement
of its parameters.
From 1996 until 2000 the LEP collider is operating at increasing energies
up to more than twice the mass of the Z0.
The main aims are to discover the Higgs boson if its mass is small enough
and to measure precisely W-pair and Z-pair production to establish the
triple gauge boson couplings.
The muon chamber electronics of the L3 detector is being enhanced
to efficiently detect cosmic muons. The first results in terms of muon
momentum spectra are expected soon.
The DØ detector at the
Tevatron
proton-antiproton collider
of Fermilab
is being upgraded to cope with the increased luminosity of the Tevatron.
DØ has already been very successfully operated in a first Tevatron run
between 1991 and 1996. In fact, the top quark has been co-discovered by the
DØ and CDF experiments at the Tevatron in 1995.
From 2000 onwards the Tevatron will be in operation again with the world's
highest collision energy of 2 TeV.
Another hadron-hadron experiment
(ATLAS)
using the LHC of
CERN is under
preparation and is expected to give decisive information on the existence of
the Higgs particle.
In an international context, with the agreement of 19
European governments to build the Large Hadron Collider
(LHC) at
CERN, this
field of research has become a European priority for the next 10-20 years.
Japan has joined into the construction of LHC and about one third of the labs
participating in experiments with
LHC
are American (U.S.A. + Canada).
The
involvement of Nijmegen in necessary detector development (electronics and
computer science) has an important potential for spin-off for e.g. medical
application, with exploitation depending on available human and financial
resources.
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