Questions and Answers from Virtual Ask-a-Scientist of February 2, 2002
More information about the program
Moderator (this is Robin Erbacher, researcher at Fermilab)
Welcome to the Virtual Ask-a-Scientist program. I am
Robin, the moderator. Sitting next to me is Roger, the guest scientist for
today. We are ready to begin when you are. Fire away!
What, exactly do you do there at Fermilab?
I do a few different things here, but my main thing is
my research. I am working with a group of people who are looking for what most
of the Universe is made of. It turns out that whatever it is, it is missing. We
would like to be able to detect it in a laboratory on earth. So, that is what I
am spending most of my time doing here-- working on the Cryogenic Dark Matter
Search (CDMS). Check out this link for more information on CDMS.
Is Fermilab currently running an experiment in the
Hi Barb, Yes, Fermilab is currently running two
experiments in the Tevatron, the world's highest energy accelerator. We are
colliding protons and antiprotons to study fundamental particles. Here is a link
to a nice site that shows live events from the two experiments, CDF and Dzero,
as well as the status of the accelerator itself. Check it out!
What exactly is Dark Matter? Do we know what kinds of
properties it may have or importance it may be to the field of science?
Good question, Kyle. We don't know what dark matter
is-- exactly. We see lots of evidence for it when we look out into the universe
and see how things are moving out there. We think we understand the laws of
gravity and that tells us there is a lot more out there than we can. But, we
only have theories as to what it might be. The best one seems to be a kind of
elementary particle that we have never detected directly on earth. We hope that
it interacts weakly so we can detect it in detectors in the Laboratory. It is
important to science because it influenced the way the entire universe evolved.
Without it we would not have galaxies, stars, or structure.
Why do you have bison there at Fermilab?
We have bison at the laboratory because our first
director, Bob Wilson, was from Wyoming and he was attempting to re-create the
atmoshpere of the prairie here. It worked.
We have a description of many of the natural aspects of
the laboratory along with pictures on our website. Here is a description about
the bison: http://www.fnal.gov/pub/about/campus/ecology/wildlife/bison.html
What experiments at Fermilab are related to
We have 3 experiments at Fermilab that are
astrophysics. The first is the Slaon digital sky survey which is mapping out a
good bit of the sky using a telescope in New Mexico, my home. The second is the
Pierre Auger project which is setting up in Argentina to look at very high
energy cosmic rays in the hope of figuring out where they come from. Finally
there is my own, CDMS, which is currently runniing under the campus at Stanford
to look for dark matter. We are presently installing a better version of CDMS in
an old iron mine in northern Minnesota where we hope to actually be able to
detect the dark matter. We also have a terrific astrophysics theory department
Should be Sloan instead of Slaon-- I need a spell checker here!
The Fermilab Astrophysics Theory group is indeed very
active, and has a website at: http://www-astro-theory.fnal.gov/
Where will the next accelerator be sited?
The next large accelerator in the world will be the LHC,
the Large Hadron Collider. This is currently under construction at CERN, the
European particle physics laboratory that is located near Geneva, Switzerland.
The LHC expects to start taking data toward the end of this decade. The United
States is collaborating on this experiment. After that, there is a proposal to
build a Linear Collider, which will collide electrons and positrons, but the
location has not been determined.
What's the connection between sub atomic physics and
Good question. When it comes right now down to it, the
whole universe is ultimately made up of particles, so it makes sense that we
have to understand particle physics pretty darn good to understand what is going
on in the Universe. Now let me give a specific example. Dark Matter-- sorry that
is our theme-- we have good reasons to suspect that it is some kind of
fundamental particle that we may also be able to produce in the laboratory. We
haven't produced it yet, and we haven't detected it yet on earth, but we
certainly see its effect on the universe. Note that understanding how the sun
works was not possible until we understood a good deal of nuclear physics. We
are learning more about it by studying things like neutrinos which are produced
in the sun. It goes on and on.
The concept of astrophysics and anti-matter is very
interesting. What sort of college education is required to enter this field of
The answer to this varies. It depends on what exactly you
want to do. In general, to become an academic (laboratory physicist or
university professor) you would have received a Ph.D. in physics from a
University, and then would go on to become a postdoctoral research associate for
a short term before being eligible for a permanent position. I am currently a
Research Associate at Fermilab. If you just want to learn more about particle
physics, there are lots of nice books and websites on the subject.
Reading through FermiNews, I see mostly male physicists.
Are there many female physicists?
Good question, Rob. I would say that there are not nearly
as many female physicists as male, but our numbers are increasing. I'm female,
and I really enjoy my work! As more women enter physics, the pathway becomes
paved for future women. The numbers have been increasing steadily as more girls
are exposed to science and realize what fun it can be!
Can someone please explain this whole antimatter thing?
No. But, we do know something about it-- like it
actually exists, we make it at Fermilab, and we use it to collide with protons.
It turns out that antimatter was predicted before it was found by a famous
physicist named Dirac. He was a theorist. He was trying to put quantum mechanics
and relativity together, and his equations had a whole set of solutions for
particles that had not been observed. They had different properties, or opposite
quantum numbers for than the particles that were known. It turns out that every
particle has such an "anti" particle. Why the entire universe is matter and not
antimatter is another good question, but then you didn't ask. We might know
somethiing about this from our studies of and certain assymmetries we have found
there, but I am off on a tangent.
What do you think will be the next big breakthrough at
I would just guess that it might be the discovery of
the Higgs, but supersymmetry and dark matter (which may be the same things)
would be another good possibility.
I'm particular interested in the medical applications
of high energy physics. Can you point me to some good resources?
There are too many applications of our work to medicine
to describe here, but for example, the MRI that you would find at a hospital
stands for Magnetic Resonance Imaging. In our field we call it NMR, nuclear
magnetic resonance, and it is a useful tool both in physics and in medicine.
Here at Fermilab we use our accelerator to treat cancers, with a wonderfully
successful program. Here is more information about our work:
Are the mechanics a solar system like ours subject to
the same law of physics as particles at a sub-atomic level? Maybe this is naive,
but at some level, is our sun like a giant nucleus and the planets like
The answer to your question is yes and no. The laws of
physics are the same everywhere, and everyone must obey them. But, the primary
force holding the solar system together is gravity while the primary forces
holding an atom together are the electomagnetic and strong forces. It turns out
these forces are much more important on the distance scales associated with an
atom. Gravity is more important for large scales. Quantum mechanics also
influences the way very small particles behave, so the behavior of an atom is
very strange if a solar system is your norm.
I'm interested in taking my family to visit Fermilab. Can
Fermilab used to be open to the public daily. Now we are
in a heightened level of security, but we are slowly adding back our public
programs. Unfortunately, there are still restrictions. There are guided tours
available, and we have just restarted our live Ask-a-Scientist program, held at
the Lederman Center on Saturdays from 1-3pm CST. You are welcome to join us
there and speak with us. See http://www.fnal.gov/pub/visiting/tours/index.html
for information about visiting Fermilab. In addition, we have an Art and Lecture
Series to which the public can come. See
http://www.fnal.gov/pub/events/culture.html for our cultural events. The public
can attend Fermilab colloquia, as well, provided they go to the Lederman Center
ahead of time to receive a visitor's badge, and provided they have a Fermilab
Supersymmetry is a theoretical idea that has yet to be
verified by experiment. It turns out that several problems in particle physics
would be cleared up if supersymmetry were to exist, so theorists tend to like
the idea. But, it has not shown up yet in our particle physics experiments. One
could argue that it should have. The theory predicts an entire set of particles
that are the partners of the known particles, much like the case for antimatter.
It may be that they are too heavy to have been discovered yet. We are still
looking. Also the lightest supersymmetric particle could be the dark matter.
There are good theoretical reasons for believing that this may be the case.
How much is Fermilab's annual budget?
Our most recent annual budget is listed as $297 million
dollars. Here is a nice link that describes some of our expenditures.
http://www.fnal.gov/pub/about/organization/budget_statistics.html This may
sounds like a lot of money, but relative to many other government programs,
particularly defense, it is really small beans. But for a huge payoff in
Can you suggest other interesting sites for high energy
Yes, there are plenty! As you may know, high energy
physicists were responsible for inventing the world wide web. Tim Berners-Lee
was working at CERN, the European high energy physics lab, and created a
mechanism to make documents public. SLAC, the Stanford Linear Accelerator Center
had the first website in the United States, after Berners-Lee called up and said
"check this out!" Here is the link to the other high energy physics sites around
the world: http://www.fnal.gov/pub/inquiring/othersites/index.html
PS, Paul Kunz was the scientist at SLAC that created the
first WWW connection with Berners-Lee.
I read something somewhere about a discovery at Fermilab
that may go against the standard model? Is that true? Can you direct me to more
There has recently been some exciting results from NuTeV,
a neutrino experiment that was done here at Fermilab. The results from this
analysis disagrees with previous results of the same measurement (but measured a
different way) by 3 standard deviations! See the press release here:
http://www.fnal.gov/pub/presspass/press_releases/NuTeV.html It is unclear if
this result is due to a lack of theoretical understanding of some aspects of
strong interactions or whether it really shows a problem with the Standard
Model. Either way, the results are exciting!
Does an accelerator have to be that big?
Well, maybe we should talk a little bit about why
accelerators have gotten bigger and bigger. There are only a couple of ways we
learn about the "stuff" around us. We can touch it, we can hear it, etc., but
one of the most fundamental ways we learn about things is through sight, and
that is basically what we are doing with our accelerator. When you do this at
home you use might use a flashlight. You shoot it at something you want to know
about, the light bounces off, and your eyes detect part of it. Then you think
you know something about the object. So, why don't we just use a flashlight at
Fermilab. The answer is based in quantum mechanics, which tells us how very
small objects behave. It turns out that quantum mechanics tells us that to learn
about the smaller, or finer details of anything, you have to have beams of
higher energy. The higher the energy, the finer the detail. So, we have to make
high energy machines to get down to seeing objects like quarks. Why are high
energy machines so large? It turns out that the higher that to accelerate
particles to higher and higher energies, you have to pass them through a cavity
that gives them a kick each time they go through. As the energy gets higher, it
gets more and more difficult to bend them in a circle and bring them back to the
cavity. This bending is accomplished by dipole magnets. Since you can only make
the magnets so strong, you have to make the circle that the particles travel in
larger and larger. And, that is why we have such large machines and want to
build even larger ones.
How does the research being done at FERMI Lab compare to
what is being done at CERN in Switzerland? Is it possible to tell who is closer
to the next big discovery like the Higgs particle?
At CERN, the LEP experiments, in which electrons were
collided with anti-electrons (or positrons), completed there work in about 1999,
and are currently publishing their final results. Some of these experiments
reported an excess of data in an interesting region of energy, and some people
believe that this may be a "hint" of a higgs boson in their data. Currently the
baton has been passed to the Tevatron, where we will be able to look at this
energy region to see if we see similar signals, or if the signal isn't there. At
the end of the decade, the LHC (large hadron collider) will come online and be
able to reach even larger energies, and we hope to be certain by then about the
existence of the Higgs in our currently accessible experiments.
Is it safe there?
Yes. Fermilab is as safe, or safer than most industrial
complexes. Yes, we do have accidents. Things fall on peoples heads, they trip
over cords, you get runover walking to work (this happened to me in January),
but there are no unusual dangers here. Our safety systems don't allow us to be
in the accelerator enclosure while the beam is on. That would not be a good
idea. It is safe to be there when the beam is not on. That is what most people
What different types of physicists work at Fermilab?
Good question. Primarily, the physicists are what we call
"particle physicists" or "high energy physicists". These come in several types.
Experimentalists are the ones that design, build, and run the experiments, as
well as analyze the data. Phenomenologists typically combine theoretical
knowledge and skill with the results from the experiments to make statements
about theoretical predictions or the implications of results. Theorists often do
some phenomenology, but they also do lots of calculations, from the accepted to
the speculative. All of our work put together makes the field very strong. We
also have accelerator physicists, engineers, nuclear physicists,
astrophysicists, and atomic physicists that work here.
It seems like CDF andD0 are trying to do the same thing.
Am I right about that? Why does there have to be two detectors?
CDF and Dzero are both Tevatron experiments, and will
both be looking at data in the next decade. Two experiments are always prefered
over one for several reasons. First, it is good to have a cross-check for our
results. For example, when one experiment started seeing a hint of the top quark
in the 1990's, the other could check their data to find the evidence there as
well. Also, since the detectors are different, and have different strengths and
weaknesses, we consider them to be complementary to each other, and both are
needed. Right now we are extremely happy to have two independent detectors,
because in our field we need as much data (as much statistics) as possible, and
with both experiments we can combine our results and reduce the errors on our
Seems like the site Fermilab resides on would be some
pretty valuable farm land. Does Fermilab have to be there?
It turns out that Fermilab is on some pretty good farm
land. At least I see some good looking corn growing out there. Part of the site
is still farmed. The answer to your question is that Fermilab does not have to
be here, but it has not made all that large an impact on the farming in the
area-- not nearly so large as all the subdivisions that surround us. To my mind,
the Laboratory has been great for the area because it has preserved a little
open space where there is still some farming going on, there is forest, there
are all sorts of wetlands birds and animals. It is great for the area. We need
to set aside more land like this.
I was looking at the live event displays. What do they
They show you sample events that are being registered
in our two big collider detectors at the Laboratory. If you look at the displays
you see the data from the tracking chambers and calorimeters in a format that
lets you see the tracks coming out from the interaction points and see the
energies deposited in the calorimeter.
Can the energy of a photon be converted into mass?
The answer is yes-- more in a second. Okay, more
details. It turns out that mass and energy can be converted to one another, no
problem except that you have to obey both the law of conservation of energy and
conservation of momentum. This puts a little constraint on you. Anyway, the most
common way to convert a photon into mass is that you run it into some material
and convert it into an electron and a positron. Of course, you also have to
conserve a few other things, like charge. That is why it doesn't convert into
just an electron for example.
I'd like to be a physicist. Is it a good job? How's the
Being a physicist is very challenging and time-consuming,
but most of us really love what we do! It takes a lot of training and often
takes a lot of time, even on the weekends and evenings. We also don't get paid a
lot, compared with many business people, although it increases as your seniority
goes up, particularly for professors and senior scientists. But we don't do this
for the money. We do this because we are interested in exploring the nature of
our universe, and of matter. :)
What could the discovery of the Higg's mean for the fields
of physics and chemistry?
Hi Kyle, I don't know if it will imply anything, really,
for the field of chemistry. For particle physics, it could mean a lot. If we
find evidence for a Higgs boson, one of the first things we will try to discover
is whether or not there is only *one* Higgs (the "Standard Model Higgs") or if
there are more. There is a theory called "supersymmetry" or SUSY that suggest
there should be four different Higgs-type particles. Both or either of these
findings would have many implications for the Standard Model of particle
Did the experiment that CDF ran in march of 2001 bring
any new or unexpected results?
Hi Julia, I work on CDF, and we are currently studying
our detector ("commissioning it") as well as looking at the data that are coming
in to see if there is anything interesting there! CDF and Dzero will likely both
begin to publish first results from Run 2 of the Tevatron, which began in March
2001, by this summer. We have now had some time to understand how our detectors
perform, and to begin to calibrate them (determine energy scales and so forth)
so we are looking forward to a very successful run with lots of papers full of
I've heard there's been digging and blasting around
Fermilab lately. What's that all about?
It turns out that we are doing the construction for a
very exciting project. We are building a neutrino beam that is aimed at the
Soudan Laboratory in northern Minnesota. The neutrinos will be produced using a
beam that comes from the main injector here. It will pass through a detector
here on site and then cut a cord across the earth and finally pass through the
Soudan Laboratory where another detector will register a few of the neutrinos.
The idea is to compare the beam as it leaves here with the beam that passes
through the detector up there. We believe that some of the neutrinos are
changing into different kinds of neutrinos enroute. These changes are called
neutrino oscillations, and we want to study them in detail. If they exist, and
it seems they do, it means that the neutrino has a little bit of mass. There was
a time not so long ago when we thought the neutrino was massless.
JuliaWow, what are the chanses that you will discover
Well, that depends on how generous Nature is! For
example, if the Higgs particle exists at energies below around 180-190GeV, by
the end of Run 2 we will hopefully be able to at least see first evidence for
it, though we will not necessarily be able to claim "discovery". If SUSY exists,
we hope to begin seeing evidence for it very soon.
Geruce has asked about the CDF and Dzero experiments.
Both experimental collaborations have nice websites. Here is the CDF website,
click on For the Public: http://www-cdf.fnal.gov/ Here is the Dzero website:
http://www-d0.fnal.gov/. Here is a link to live events from CDF and
Dzero... your answer is coming: http://www.fnal.gov/pub/now/index.html
Thank You Very Much.
It seems like there's a lot of other things going on at
Fermilab besides physics (concerts, art gallery, etc.). Does that take away from
No. You can't be focused 24 hours a day for very long.
You will run down pretty quickly that way. Anyway, the idea of all the
activities at the Laboratory is to create an atmosphere that is conducive to
creativity and good work, whether it is scientific, engineering, or whatever.
I'm sorry, but I don't really understand what's the
difference between and Astrophysist and a Particle physicist. Could you explain?
Particle physicist are primarily interested in studying
fundamental particles in the laboratory, measuring all their properties, and
all. An astrophysicist is interested in understanding what is going on in the
cosmos. Of course, this is not possible with the benefit of the knowledge that
comes from particle physics. As a result, many astrophysicists are pretty good
particle physicists too.
Where could I find more informaton about the steps the
particle beams go through before entering the Tevatron?
Hi, we have lots of information about the accelerator
complex here at Fermilab, including a cool picture of where it all begins (the
It seems like there's a lot of "flip-flopping" about
Neutrinos (ha!). What's the latest thinking?
Yes, it appears that neutrinos are doing some
flip-flopping. The three kinds, or flavors, of neutrinos can change from one to
the other. This is relatively new information, and it is exciting to particle
physicists because it is one of the indicators that the standard model of
particle physics must be modified.
I am curently a sophomore in high school. How do you think
the fields you are currently studying will change as information is gathered and
technology evolves? Will we be likely to find particles even more elusive than
those being sought after now?
Hello Kyle. High energy particle physics is very
dependent upon technological innovations. As the energies and the "luminosities"
(number of total particles) of the accelerators go up, the amount of data that
comes in at any one time increases dramatically. We therefore need better and
faster detectors and triggers, as well as faster computers and larger storage
(disk and tape and processing speed) capabilities. High energy physicists also
participate in developing new technologies specifically for our experiments!
There is a similar laboratory that is now being built at
CERN, Switzerland. What is going to be Fermilab's main focus when it is open in
This is a very good question. Right now it looks like the
Tevatron may run past 2007, but this depends upon when the LHC at CERN begins to
publish physics results. There are lots of proposals for experiments to be built
and performed here at Fermilab, including very good fixed-target experiments.
One highlight will be the NuMI-MINOS project that is under construction here at
Fermilab. This is an experiment designed to study the increasingly interesting
neutrino particles. In addition, currently the Mini-BooNE experiment is gearing
up to be run beginning sometime this year (concurrent with the Tevatron, but
during a downtime of the Tevatron) to study neutrinos as well!The future for
Fermilab past this decade is now being discussed and debated. Many physicists in
the U.S. would like to see the next big accelerator built here: a large Linear
Collider that would collide electrons and positrons at high energies (500 GeV to
perhaps 1.5 TeV or so). There are also proposals to build the linear collider in
Germany and Japan, though, so who knows? Other scientists here would like to see
a VLHC built here, an even higher energy hadron collider. But this would be on
an even further time scale.
So Weakly Interacting Massive Particles are "WIMPs"? Who
names these things?
Not me!!! Whoever did it is probably quite proud of
themselves, but here I am doing research where I have to live with it. Anyway,
when you write it out, it does make sense. That is what we are looking for--
weakly interacting particles that are probably heavy (WIPTAPHs-- there, that's
better.) By the way, it used to be MACHOs vs. the WIMPs. MACHOs were thought to
the the dark matter by some astronomers for a while. They are Massive Compact
OK--Who REALLY discovered the Top Quark first? You can
I think it was James Joyce, but it is not well
documented. Anyway, the real story is that CDMS saw evidence for it first, and
then the Dzero and CDMS collaborations zoomed in on it at the same time and
announced the discovery together.
I meant CDF-- I guess my bias for physics is really
Are there any opportunities there for high school
Yes! If you are local, you can participate in Saturday
Morning Physics, which Roger helps run:
http://www.fnal.gov/pub/education/index.html In addition, there are summer
programs for students interested in science. You can browse through on this
I'm looking at the webpage where you can see the CDF and
D-0 results every 15 seconds. Do you run experiments all the time or are there
different set times for that?
Hi Julia, When the Tevatron is running (when there isn't
"downtime" for repairs, upgrades, studies, or other experiments) we operate the
accelerator, and thus the CDF and Dzero experiments, 24 hours per day, 7 days
per week! This means that there are people "on shift" in the Main Control room
that controls the accelerator, in the CDF control room, and in the D0 control
I'm particularly interested in the architecture of
Robert Wilson. Can you point me toward some info?
Here is the link:
Can someone help me with a lesson plan on WAVES for
14-15year old highschool students. Thanks.
We do have a lot of high school physics and science
teachers that work with Fermilab through a program called Quarknet, along with
other programs. They might be a good resource for help at the high school
science level. Please send a note to the education office or to Quarknet at:
http://www-ed.fnal.gov/ed_home.html or at: http://quarknet.fnal.gov/
Thank you very much for all the answers!
I've heard there are many photos and information about
birds on the Fermilab site. Where can I find that?
Hello Papageno! Please see:
Is there a live "Ask-a-scientist" program at Fermi?
Oh, you and I think alike! Yes, see my previous message:
Saturdays at 1pm CST, use the Pine Street entrance to Fermilab and come to the
See you next time!
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