Say you’re driving down a highway with a
friend and suddenly you see something completely
weird or strange like a Bigfoot-like character
running through the woods or a fireball flashing
across the sky.
What do you do?
You immediately turn around to your friend
and you ask, “Did you see it?”
So our natural reaction whenever we see anything
unexpected or strange is seek independent
confirmation.
And in this case if the friend were to come
right back and say, “See what?” you sort
of question your initial observation.
So the ATLAS and CMS experiments at the LHC
essentially rely on the same philosophy.
They are two distinct experiments, but they
are using and looking at the same high-energy
LHC collisions and recording the data.
If one experiment were to see something unexpected
or exciting, one would then turn to the other
experiment and ask, “Did you see it?”
And of course such an independent confirmation
makes sense only if the two experiments are
completely independent, autonomous.
And the idea is that if both experiments see
the same new phenomena, one would have greater
confidence that what you observed was real
and not a random fluke or a coincidence.
So the first big, obvious difference between
ATLAS and CMS is the size.
ATLAS is huge.
It’s about twice the length of CMS but actually
lighter in comparison, about half the weight
of CMS.
At the heart of CMS is a powerful solenoid
magnet.
It’s the largest magnet of its kind ever
built.
And using its very high magnetic field, CMS
is able to measure the momentum of charged
particles such as muons and electrons very
precisely together with an extremely precise
tracking detector.
ATLAS, on the other hand, does not have such
a powerful solenoid magnet.
However, it has an excellent stand-alone muon
detector, which measures the momentum of muons.
So the two experiments, of course, are very
distinct.
They have different technologies.
And in this case while ATLAS and CMS have
been built quite differently by different
groups of scientists, in the end they are
looking for the same kind of new physics.
