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the ACME Collaboration presents
the Electric Dipole Moment of the Electron. Why is the universe made up
of matter?
Why is mostly that matter mysteriously invisible?
These are just a few of the fundamental questions that the ACME experiment is
trying to answer by studying one humble particle,
the electron. The most successful theory of particle physics
is called the Standard Model. It says that everything is made up a small
collection
basic particles and it tells us how they interact with one another.
this theory explains everything from electricity to the existence of the
Higgs boson
and it does so extremely accurately. But the universe
still holds mysteries that we think the standard model cannot solve.
One of these mysteries starts at the Big *** when
according to Einstein's formula E=mc^2,
a giant flash energy was transformed into objects that have mass.
In the standard model this transformation energy requires that for
every particle created
a partner anti-particle was also created. If a particle and its anti particle
encounter each other, they annihilate and convert back
into pure energy. The strange thing is that the universe we see now is almost
completely made particles
rather than anti-particles yet the standard model doesn't explain how there
came to be more matter than
anti-matter in the time from the Big *** to now.
Another big problem is that most of the stuff in the universe
is made up particles that are not part Standard Model.
Astronomers know that there's hidden dark matter that we can see with our
telescopes
but whose gravity effects the ordinary matter that we can see and understand.
Some clever physicists have come up with possible solutions to these problems,
and other ones. Most of their theories include a zoo of exotic new particles
which have yet to be discovered. Some of these new particles could account for the
matter that we can't see
or could interact such a way that would result in all in antimatter getting
destroyed
while some matters survives. At particle accelerators like the Large Hadron
Collider
physicists are trying to create these new articles by violently smashing
protons together.
From sufficient energy new particles can be created
just in the Big ***. This is how most to the types of particles that we know
about were discovered,
and we hope to find someone the new predicted articles in this way.
The ACME collaboration is looking for new particles in a very different way
by making a precise measurement of a familiar particle: the electron.
We are trying to measure the electron's electric dipole moment
which is the distance between the electron's center of mass and its center of
charge. The electron acts as an antenna
sensitive to the presence of the weird quantum mess of particles
surrounding it all the time. Some of the exotic new particles that theorists
predict
should give the electron a dipole moment large enough for an extremely precise
experiment to measure,
but still astonishing tiny. Our experiment is sensitive to a dipole length of
one tenth of a billionth of a billionth of a billionth of a centimeter.
To understand just how small this is, imagine blowing the electron up to the size
of the solar system.
The displacement our experiment is sensitive to would be the same as the
diameter of a needle.
To look for this dipole moment
we use molecules called thorium monoxide. The highly-charged
thorium nucleus act as a hugely powerful amplifier for the signal from a dipole
moment
of an electron in the molecule, and the presence of the oxygen
acts as the volume *** which we can turn up to maximum by turning on an electric
field in our lab and aligning
molecules. Thorium monoxide has the biggest
amplification at any known molecule. It increases our single size by a factor
one billion. Through careful use of lasers we can watch how the electrons within
these molecules behave
as they pass through our experiment. Because this effect is so tiny
we have spent months carefully looking at the data double checking our work to
make sure we are looking at the signal due to the electron's dipole moment,
if there is one big enough to see, rather than some other spurious
effect. Our measurement was about ten times more sensitive
previous measurements and we still think the electron has no electric dipole
moment
this suggests that some of our favorite new particle
theories might be in trouble. But the jury is still out
and we're going to keep looking.