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for our monthly guest speaker, >> Jim Lattis: Well tonight
professor Francis Halzen. Francis has been the head of
Neutrino Astronomy here for quite some years, and the
Ice Cube project is nearing a really important point in this
current construction season and he's going to give us, tonight,
a talk about the Ice Cube Neutrino Telescope and what he
calls First Light, but it isn't actually light, it's neutrinos
actually. So, Francis.
Francis Halzen: Thank you for not mentioning how long we
have been doing this. [LAUGHTER]
In my case, it's over 20 years. I understand this is the fourth
talk of a series, and so this is
lot of this has been covered. uSo I will quickly go over the a
previous talks as an
to talk to you about our first introduction, and then I'm going
science. attempts to actually do some
there will be a test afterwards. And so since am I a professor,
And so I'll first review the [LAUGHTER]
You know by know that we don't three previous lectures.
We are building a particle know what a telescope is.
thought we knew how to do and we physics detector which we
it will be finished by this actually knoweekend. do because
So that I will remind you of
detector. tThen I will tell you why it'sge
maybe astronomy, maybe not. And I will remind you a little
bit about the technology. But most of my talk, you will
have heard most of this by now, most of my talk will be about
the first science that we are trying to do with this detector.
My usual apology, there is no nice pictures in this talk.
There are no penguins.
picture. This is the last beautiful
This is an actual picture of the This is Antarctica for us.
If you look at the wrong geographic South Pole.
cube or the South Pole station, directionyou see this.t see ice
And you are standing on three kilometers of ice.
And that's our interest in
It says here ultra-transparent Antarctica.
In fact, if you take this glacier, you're standing at the
South Pole, you are moving 10 meters a year on the glacier
that comes of the west Antarctic
And if you go all the way to the mountain range.
and so you have to imagine that cwe are at the South Pole, this
is three kilometers thick and we
the middle of this. arAnd this is why I'm standingin
here. We actually discovered that
light travels 100 to 300 meters in this ultra-pure ice.
It was a total surprise,
In fact, you have to realize we would never have started this
project if we had had glaciology
was more like eight meters. bookWhen people measure theumber
transparency of tap water, light
going extinct. travels about two meters before
about eight meters. If you make bubble free ice and
test it in the lab, light travels eight meters.
Fortunately, we didn't know any of this or we would never have
started.
we had the blessing of being So we are particle physicists so
[LAUGHTER] totally ignorant.
surprise that this ice But we discovered to our
you cannot compete with it with acthings you make in the lab.at
You couldn't make a solid that's
It's ultra-pure condensed of as transparent as this ice.
that fell on Antarctica. some hundred thousand years ago
what counts. So it's ultra-pure and that's
Now comes the review. SoWhat are neutrinos?e.
In two slides.
that the world is made of protons and neutrons, and the
protons and neutrons make nuclei
uranium. like alpha particles, helium,
around it, they make atoms. And that's what you learned and
that was not your money's worth,
because we wouldn't be here if wherever you learned this,
there is also a neutrino. it And how do we know this?at
We know this since the 1930s
it decays into a proton and an because when a neutron decays,
neutrino, whenever the proton goes this way, the electron goes
that way. It's billiard ball physics.
In fact they noticed that occasionally the proton and the
electron would go that way which
that way. meAnd they say, well, it's ago
particle and it's saves momentum
And in fact it doesn't interact with anything.
And so that was it. It was like a mathematical
trick.
But you have to remember that the neutrino is kind of an agent
that makes nuclear physics
Without changing neutrons into possible.
physics, there are no nuclear reactors along Lake Michigan,
there is no sun that burns and
So we wouldn't have sunlight, and we wouldn't be here because.
the stuff we are made of is made
So the neutrino is important, but people realized that it was
just like light.
charge, no nothing. So it was just like photons
except photons don't go through walls and neutrinos do.
That's the only difference. And so that may be good actually
because if they go through walls
cores of black holes and that mallows you to do astronomy your
cannot do with slide. That was kind of the fake idea.
This sounds all good until you
[LAUGHTER] hear the rest of the story.
discovered the neutrino as a In fact, the person who
have done a terrible thing, I have invented a particle that
cannot be detected. [LAUGHTER]
And when we were in the beginning trying to build
AMANDA I would always tell my collaborators we're going to
prove him right.
It never went over very well. Now this slide you have seen
before, I'm sure. It gives you an introduction in
two slides again to multi-wavelength astronomy.
This is the explosion of the
When this happened, you could read your newspaper, or whatever
they wrote in, for three weeks
And so that's what it looks like during the day.
There is a pulsar in the center, now, a Hubble picture.
explosion a thousand years and this is a picture of the
And so that's the same picture later.
So the next case this is a -- picture taken with a satellite.
And you see this picture is only
streams of high energy particles a few years old, and you see the
seen before. coming out that have never been
is take a picture of the crab, And so what we want to do
Although we're almost sure that the crab doesn't emit any
neutrinos, and if it does it
them, but we will find them if will take us 10 years to find
don't worry. they can be found in 10 years,
around the world with. This is the excuse we went
--, we went around saying we You know, as soon as we told
So isn't this great? can build a neutrino telescope.
telescope, look at all these Look, whenever we build a
And so you know we build this and we don't know what we'll see
but it will be great. [LAUGHTER]
Just like in the past.
wrong place, in Washington. And someone came over and said,
you know, it was from the Office
said, what you're saying is that of Management and Budget, and he
money, gamble with it and we'll you'resee what comes out.rnment
Doesn't sound very good.
And this is what he told me. I said, what do I say instead?
There are administrators [LAUGHTER]
Okay, so you get the idea. with a sense of humor.
The last thing is how we detect The summaryneutrinos. finished.
Now, I told you neutrinos for 20
concept until this man, Reines, he had to wait another 20 years
to get a Nobel Prize for it, but
produced where there are nuclear he knew that neutrinos are
He went to the Savannah River nuclear reactor and put a small
detector about a meter. And you see here it's basically
water and photomultipliers. And so he put it close to a
nuclear reactor.
of neutrinos so you can do it And ywith a small detector.flux
And he did it.
He told me that as soon as he detected neutrinos he had the
idea that you could do astronomy
In 20 years nobody had told about it.
But it's strange, once you know something is real you suddenly
get this idea that nobody had had before.
And in fact he was not the only one.
Someone else had the idea,
had the idea. and a mAll in the 1960s.d Markov
This experiment was 1956. Unfortunately, this beautiful
dream went home when people started doing some calculations
and realized that you needed a
So what we need is this detector kilometer scale detector.
kilometer. but instead of one meter, one
And so since the 1970s we have That's all.
And actually, next weekend, unless something goes wrong,
it will be a reality. In fact we have a detector
that's much bigger than a kilometer cube even if we don't
get the next two strings in.
idea of how to detect these So this isneutrinos.o had the
So this is what he wrote in his paper in 1960: We propose to
install detectors deep in a lake
direction of charged particles or in a sea to determine the
It doesn't matter. with the help of radiation.
That's what I will explain in a You unminute.d this.
But why did it take so long?
water which was the wrong It is becaumedium.alked about
And so we had the idea in '87 after people had been trying
this in water, forget it. We are going to do this in ice,
not knowing that ice may not be very transparent.
And so you heard the story. We drill holes in the ice, put
light sensors in it and all this
And so that's the idea. You go a mile deep under the
glacier at the South Pole.
kilometer cube worth of light You go a msensors. and put a
It's totally dark so you can't
your neutrino. detect light, and here comes
It goes right through your And what does it do?
It has already gone through the earth, it goes through your
detector, but these are light sensors.
So here is a, it's called a photomultiplier and it detects
light.
dollars and put five thousand of Buy it in Japan for a thousand
And so once in a while, actually them in the ice.
instead of going through the about once in a million times,
protons and a bit of oxygen, a ice, a neutrino, ice is made of
a proton. neAnd then a nuclear reactionnto
happens.
light. And nuclear reactions produce
most interested in, it does this And in fact, in the cases we are
It actually produces a slash of nuclear particles, but among
these particles there is this muon and this muon can travel a
long way. And when it travels through your
detector, it leaves this wake of
you use your sensors to map this light and it's blue light and
From this wake you never see the wake.
where the muon came from and the muon, but this wake tells you
direction. neutrino comes from the same
neutrinos, you know where they So you know to only detect
telescope. come from and you have a
somewhere on the other side of You know where they come from,
So from the South Pole we are looking at the sky above us,
looking for neutrinos that
So if you didn't quite get this, travel to the earth.
better. Blue light from a nuclear
reaction, actually, you have to realize this is a very faint
nuclear reaction. And most of the time what we
detect is not a lot of light. In fact, typically we detect 10
photons.
And these light sensors typically detect one photon.
So we require that eight of them
event. fire and that's what we call an
So it's not as easy as it sounds.
This is a nuclear reactor, not a
And you see it's covered with newater..
And all the nuclear particles coming out of the nuclear
reactor, including very few muons, they made the water glow
just like these particles make
And so this is the color of the light we see in the ice.
And so where does this wake come
The wake, first of all I already from?
This muon at high energy travels explained, it's very important.
see neutrinos outside our kilometersdetector.n actually
And so the detector is actually much bigger than the kilometer
cube instrument with
But the wake is what gives away the direction of the neutrino,
and that's what makes the astronomy possible.
And this is the physicist's explanation, but this is the one
that's easy to understand.
The muon travels at the speed of This is the muon.
So it tickles the atoms in the light or very, very close.
But that light is slowed down in ice and the atoms emit light.
So it's going at the speed of light in ice which is
significantly less than the speed of light.
So it goes at the speed of light
than the speed of light which but tmeans you get a wake. less
And if you measure this wake
know where the duck is going. with our pThat's it.liers, you
Okay, so we started somewhere in
my first talk to this audience the early '90s, in fact I gave
Steakhouse. And so we started at that time,
we were thinking about building a detector we called AMANDA.
So this is the South Pole, and
the year 2000. this detector was completed by
You go 1500 meters deep and then And it's the same story.
photomultipliers and we started there trying to do this.th of
We knew this detector was much
When you read the proposal it says we want to test whether we
can build a kilometer cube
And in fact we give the price. detector.
inflation, it's exactly what we And if yspent.rect for
We're very proud of this. So now we see neutrinos with
AMANDA. And I can remember the day I saw
the first neutrino event from AMANDA.
It was one of the great thrills of my life.
I won't say where it hangs
people. becBut this is a neutrino. of
And once you find it, you know
You can bet your house on it. So you see, remember you want to
see a track coming through the
It comes from the bottom, from ice.
Each of these dots is a photomultiplier tube.
So the length of this track, you
Ponderosa Steakhouse, it's about track from about here to
And you see the way we are going that far.
events, that's my job here to look at a lot of these
dots. Whenever you see a colored dot
it means that the photomultiplier detected one
photon. So you see these little dots,
that's one photon.
late. TSo you follow the rainbow ands
that tells you the direction
And when you see big dots, it means that the photomultiplier
detected a lot of photons.
here so this dot is like 12 You can seephotons.e of a dot
But you see without looking at
tell that this track comes in thhere and goes out 300 metersan
later at the top. That's a neutrino.
So it worked. So then we started, we proposed
in 1999, in fact a year before
work. AAnd we proposed the ice cube.is
And this you can seen many times
Eiffel Tower. And this is the AMANDA detector
which worked for nine years until it became insignificant
and we turned it off a year ago.
cube filled with 5,160 And so it's just a kilometer
one and a half and two and a photomultiplier tubes between
And what it does is, in fact half kilometers.
this was good precision, it idetects 220 neutrinos per day,
but it also detects 1.7, almost a billion cosmic muons per day.
And that's a problem which I'll come back to later.
That's the hard part of the story.
And we'll ignore this at the
220 neutrinos per day. moment and concentrate on the
later. I'll tell you about the muons
background. TTwo thousand per second.
They come from a buff.
They're cosmic muons. You have to deal with it.
You have to measure them and
And that's what we do every second, 2,000 times.
So on top of the ice there is a big computer center that takes
care of this. Where are we?
I've referred to next weekend.
from the top. WSo if you look on top of the
ice.
deployed in January 2005. And this is what the detector
looked like a year ago. And in fact as of today, these
strings have been put in, and there are only two more strings
that have to be put in at the center here.
In fact, I have to show some
I mean, the drill was maybe the hardest part of the project.
It's 4.8 megawatts. It drills holes to two and a
half kilometers.
It moves three and a half centimeters every second..
And it's a masterpiece. So here the drill comes out,
the photomultipliers are ready, 60 to go in the hole.
And then you see them go in, one
other. every 17 meters, one after the
three hours ago, and this is And if you looked at my computer
This is time versus depth. what I was seeing.
finished the hole about a day And this wasago. drill that
Three hours ago they were drilling hole number six, seven.
And you see they are already at 500 meters there and now
probably close to a kilometer.
a string. AThese little red dots is eachoy
time you attach a module one of these lines is drawn, and as
time goes on the string sinks in
You are looking at the data upside down.
And three hours ago the string
which means it's at the bottom reached the bottom, reached zero
So by this weekend, this will be of the hole.
Two more strings to go. Now before we looked at events,
here is, in case you didn't get it, here it is again, the movie.
So look at the bottom here. You'll see a neutrino arrive.
As you know neutrinos are red.
And I think they are red, I'm not sure.
Yes, they are red.
the muon makes light in the They hit adetector.ake a muon,
This light is actually
The digital signal goes up on a tracable and goes through theal.
computer that reconstruct the event.
Okay? You get the idea.
So here we go.
and that's what a neutrino looks At some point we had 22 strings,
Then the next year we had 40 strings, and that's what a
neutrino looks like, three of them actually.
They all look the same, right?
you see it doesn't make much So here, this is a neutrino that
That's a low energy neutrino. It's one we can barely detect.
It's energy is one TeV. It doesn't matter what a TeV is.
This is the same energy as the
So these are the highest Fermilab accelerator in Chicago.
except they can go a bit higher energies in Geneva now. on earth
But this neutrino is the same energy as the protons
accelerator, that Fermilab. But this, for us, is wimpy
stuff.
You can think of this, this is a This is a real neutrino.
In fact, it's not a nuclear real nuexplosion.osion.
The neutrino makes a nuclear
travels through the detector explosion but this muon when it
explosions. So you see bombs going off.
So you see a lot of light, and
In fact I'll show you one, this thone, you see red again, youo.
follow the rainbow, it goes to
times the energy of the Fermilab green, this one is a hundred
This one I have to change units. accelerator.
the accelerator. It's 10,000 times the energy of
this event very well. AWe cannot quite pin down whatnd
made it, but we only have one like it.
And it produced 250,000 photons.
talking about. Not the eight or ten I was
atmospheric neutrino, Sbut its probabilityn
is 10 to the minus three. We have more data by now, we'll
figure this out.
show this slide and this has But I want to tell you, I always
Developing this technology was a nothing to do with me.
made it to the cover of Science mmagazine without ever havinge
discovered anything.
as far as I know. TBut it was in recognition ofe
having built a kilometer cube detector.
In fact we hadn't at that point,
to. We also got elected one of the
Seven Wonders of Modern Astronomy.
That's when we were just
I am not sure we had seen a neutrino by then.
But the category is kind of questionable.
You see.
Maybe you cannot see this very well.
So let me now go back and use the rest of my time just going
to look at maps.
detect a neutrino, to point this You have the idea, each time you
comes from on the other side of way, you the earth. where it
As they, most of them, all of them as far as we know, are
produced in the atmosphere, you find a totally uniform sky.
They come from everywhere.
AMANDA for one year. So this is after we operated
one year. And so you look at this map, by
the way these are muons, this is
from the southern hemisphere. And so if you look at that, you
can see this here.
looking for. This is the type of thing you're
is a star that you see through This is the atmosphere, and this
It's actually a statistical thfluctuation..
We knew that. We expected to see a fluctuation
like that in this map.
Nobody got excited. In fact, we took data for
another four years and you get
And there's actually a hole in this map.
appeared and now there's an X somewhere else, it doesn't
matter. But you get the idea as time
goes on, it's like in the old days when you developed a
picture in the darkroom you just
clearer, except for us it takes see it becyears.earer and
And remember AMANDA was a hundred times too small to see
anything we anticipated.
technology. So here this was AMANDA's final
sky plot, and it delivered a
as it was supposed to do, almost beautiful sky with nothing in it
Then we went to ice cube and 7,000 events.
ago. this is ice cube of two years
instead of 7,000, in one year it And it delivered by now of
in its eight years of existence. produced more events than AMANDA
this map. And These are the neutrinos. in
Now, I am not going to discuss
powerful that we begin to be this, but this detector is so
sky. able to look at the northern
this huge and annoying We begin to find neutrinos in
And so at the moment, is there background of atmospheric muons.
map? an interesting point in this
It's there. There's no way you can see it.
I know where it is. You have to find it by computer.
And so now we understand this detector.
And this is what our sky map
I'm a theorist so you can run a computer program, and you can
see here you will see the sources appear.
You see these sources?
first. That's what I think we'll see
Let me try to explain this. Since 1932 people have realized
that about the only thing that
galactic cosmic rays is a cansupernova explosion.ce
Actually like the cap, they look
not a good one. liAnd so detectors have beenis
looking for these in gamma rays.
mapped the galactic plain in And this is an experiment that
are working. gamma rays at the energies we
sources except they look like Sany other gamma ray sources.e
There is no way to prove that these produce cosmic rays.
But we have.
particle physics courses, then In fact, if you take a lot of
That's for every two gamma rays yothey see, we have to see a.
neutrino and an antineutrino
So basically, if these are the which we cannot tell apart.
which everybody already believes sources of the cosmic rays,
for it, then we have to see one aneutrino for every gamma ray
they see, and that gives us this
And you know you can see the map.
It's incredibly easy. And in fact, you can ask what
about this map we just saw? So of course here it is.
I couldn't resist plotting this out and there are the candidate
sources, they are now in a
the biggest one is this star different coordinate frame, but
And you see this cluster of red dots.
And so this is maybe the
future. However, these red dots here are
two sigma fluctuations. So there's nothing to get
excited about.
years, in fact the predictions But this is on track to in five
we would declare we have are that we should get to where
have agreed on a minimum discovered something to which we
This could take as little as statistical significance.
It could take forever. three years.
man will be very unhappy If it takes forever then this
predicted in 1934 that supernova because he's the one who
this is Zwicky, and unfortunately he will not be
around but I'm sure wherever he is when he sees these sources
appear on the map he will smile.
So I have been telling you about He won't look like this.
and so that's the end of the this annoying ongoing muon sky,
This is the detector. If you looked at the detector at
any time, this is of course you realize when you see these
events, these develop at the
So I clearly have the speed of speed of light.
And so instead of coming at 2,000 seconds, they come at like
one every few seconds.
other. So you get one event after the
interesting. But there's something
These are just like neutrino Look at these events.
They are also muons like the events.
A muon is a muon. But look here, the red is there
and the green is here.
2,000 a second, you measure Sothem, throw them away..
How do they get there?
atmosphere everywhere, make pions and these pions decay into
these annoying muons which you
So you get constantly bombarded by these muons.
Here, to tell you how annoying
microseconds you see five of this gets, here in four
detector. And it's very easy to fool
yourself in this mess and reconstruct a fake neutrino some
way or another. But we managed to do this.
Remember, they are a million
neutrinos. times more frequent than
million times you have no So if you experiment.p one in a
So we are doing this now like one in a billion times we make
mistakes. I think you get the idea.
The muons come from above, which
and the neutrinos come through is from below at the South Pole,
So what we are going to do, I explained this already, but here
several billion, oops that's not
Atmospheric muons, yeah seven billion per year and about
400,000 neutrinos a year. So what we decided at some
point, I'll tell you why in a minute, we decided we are not
seeing anything this way, the detector is too small, let's
look up where we have billions
They shouldn't point any where of events.
And so you cannot see the dots but let's look up.
You cannot see a billion dots on anymore.
This is actually a probability a screen.
but you may think of it as a distribution you are looking at,
In fact this is four billion billion dots.
And we looked at this and you got the idea these muons come
through the ice from above and
of this cosmic rays which are theyproduced in our galaxy.ction
So the first thing we saw was the moon.
You know wherever the moon is,
absorbed. And you know the moon is a half
of degree on the sky. And here is the moon.
It makes a deep hole in our detector of less than one
degree, it's about
So we saw the moon. So now the next thing what we
actually wanted to see was this.
our galaxy so we try to see the Tsolar system move through theo
wind of the cosmic rays.
earth, so six months we are moving into the cosmic rays and
six months we are moving out. We didn't see it.
What we did actually see, so we thought maybe our detector
doesn't work, what we did see is
go around, the earth going let's try if we can see the sun
And there it is. around the sun.
This, by the way, has also never Beautiful dipole.
So we now know that the earth been smoves.fore.
We have seen the moon and we
So anything can happen next. know that the earth moves.
But this detector worked [LAUGHTER]
In fact, we have much better beautifully.
So here is the map. tAnd so what we saw is, so we
didn't see any of these fancy motion of the solar system but
we saw that there's a big excess
direction in the sky. oNow cosmic rays are charged.e
They are not neutrinos, they are
to make a map. not light, they are not supposed
you that all this structure in In fact among friends I can tell
real. tNobody knows what this is.
The only thing, in fact you can see this is with 22 strings,
this is with 40 strings and I have seen 59 strings and you see
how all this structure reappears
They look identical. in these maps.
detectors in the north, the Vela detector I mentioned
before, it also has annoying
And our access, in fact in the muons that it mapped.
map points right at Vela, which is the closest supernova to thes
earth.
Not possible. AnThere's no way 10 TeV cosmic?
rays can travel in straight line
to here. to the galactic field from Vela
So it's like there is no Not possible.
there. galactic field between us and
but I don't have one. We promise surprises, well, this
is the first one. And so this is, there is
something wrong with our
field or there's something wrong understanding of the magnetic
particles in the galaxy. with the fusion of charged
So keep tuned. God knows.
already proven Zwicky's theory. BuBut we don't claim this yet.ve
The only thing we claim is that we discovered something
we don't understand.
talk. So everybody, the first question
is always will we discover
we have, will we discover cosmic atmospheric earth, atmospheric
And a few years ago there was a web page, this is always in
Britain right, where you could
the probability that LIGO bedetects cavitational waves,'s
AMANDA detects cosmic neutrinos,
And in fact they gave six to one and others--.
neutrinos, which is crazy. that AMANDA discovered cosmic
In fact, we started betting on But six to one.
And I thought that was a good Lbet so when we started betting.
on it they took the page down.
You see the normalization [Lhere.ER]
Finding Elvis alive was a hundred to one, and the
Loch Ness Monster is 66 to one. I would actually have bet on the
Loch Ness Monster instead of
[LAUGHTER] AMANDA.
after the question period, But after this talk,
cash only, I give on Ice Cube I'll be intwo to one.f the room,
[LAUGHTER]
[APPLAUSE]