WIMPs
Introduction
What are they? What are their characteristics?
WIMPS (Weakly Interacting Massive Particles) have the characteristics
necessary to explain the dark matter problem posed by galactic
rotation curves.
They don't interact with matter much -- which is why we can't
see them; no interaction means no energy change and no photon
emission
They are massive -- required for explaining rotation curves--perhaps
as much as 50 times more massive than a neutron or proton. However,
they are the least massive of the supersymmetry particles.
A million WIMPS could penetrate
your thumbnail each second without being noticed.
Estimates vary but WIMPS make up as much as 99%
of the mass of the universe.
Everything you ever wanted to know about Dark matter
http://www.wordiq.com/definition/Dark_matter
Demonstrations
Demo 1: They don't interact very often
Use a marble rolling under a shield demonstration (like the
Rutherford scattering demo we saw in the workshop). Under the
board you put a single thin nail. Roll a bunch of marbles through--most
of them will miss the target. Every now and then one will hit.
Flaws in this model: There are actually nails all over the place,
and only one of them will interact every now and then. In the
prediction, the WIMP is deflected but the atom recoils, which
doesn't happen here. The recoil can ionize the atom by knocking
the nucleus loose from its electron (sort of anti-chemistry)
and create ionization and a flow of electricity as well as heat.
Demo 2: Shadow matter
WIMPS are sometimes described as "shadow matter" because they
don't interact. Set up marbles on an overhead to represent atoms.
Put a bead on a thin string to represent the WIMP. Pass the bead
over the marbles without touching. The shadow will pass over
the atoms without interacting.
Flaw in this model: We hope that every now and then the WIMP
will interact with regular matter, and in this model it never
does.
Attempts to Detect
(Mandy) DAMA - Sagittarius dwarf galaxy poster: We
drew a poster which showed how material from a nearby dwarf galaxy
being
ripped apart
by the Milky Way may be a source of WIMPS streaming at us from
the direction of the galactic center. The Italian DAMA experiment
claims to have detected WIMP events but has not been confirmed.
The DAMA detector in Italy uses a scintillation detector to
measure a change in flux of dark matter as the earth rotates
around the sun. We would expect greater flux when we're moving
with the motion of the sun in our galaxy, and less when we
are moving against the motion of the sun in our galaxy. The WIMP
is expected to interact with the nucleus of a sodium iodide molecule
in a crystal and emit photons. The detector itself is located
1100 meters underground so that the cosmic ray particles will
be absorbed before reaching the detector.
The DAMA researchers attempt to refute contradictory claims
here:
http://www.lngs.infn.it./lngs/htexts/dama/claim.html
Stanford, UK (Mike)- There are several methods in detecting
WIMPS. Detecors have been built in several experiments for detecting
these ghostly particles. In the UK, scientists have built a detector
located in an abandoned halite mine at a depth of 1100 meters
near Yorkshire. In Stanford, a different type of detector has
been built 35 feet below the ground.
http://hepwww.rl.ac.uk/ukdmc/ukdmc.html
GLAST- GLAST will provide a wide field of view. The
Si detectors that are stacked will also cause a probable increase
of
triggering the events necessary to detect WIMPS. We learned in
our debriefing that only one kind of WIMP is possible to detect
with GLAST, although that is not its primary mission. It is intended
to observe Gamma Rays from bursters and active galaxies.
http://people.roma2.infn.it/~aldo/elba02_2.pdf
UK
Supersymmetry
Supersymmetry is a part of an advanced model of high energy
physics derived from the multiple-dimension model that is used
to explain electromagnetic photon propagation and strong and
weak interactions. This 6th dimension model predicts the existence
of particles and supersymmetric particles called "sparticles."
WIMPs are the lightest kind of sparticles.
MUCH more information here:
http://www-glast.sonoma.edu/~lynnc/courses/a350/lecture_2003/L14Hyper/index.html
Links
http://treehousefun.com/read_and_learn/universe.html
Good article aimed at younger students (middle/high).
http://astron.berkeley.edu/%7emwhite/darkmatter/dm.html
General overview of Dark Matter
http://cosmology.berkeley.edu/Education/learn.html
Links
to dark matter FAQ and other cosmology pages.
http://news-service.stanford.edu/news/2000/march1/darkmatter-31.html
http://www.innovations-report.com/html/reports/physics_astronomy/report-9683.html
Recorded lecture on dark matter in cosmology
http://www.wlap.org/umich/phys/satmorn/2003/20030405/
