- Welcome everyone, Wednesday Nite at the Lab,
I'm Tom Zinnen, I work here at the UW-Madison
Biotechnology Center.
I also work for UW-Extension Cooperative Extension,
and on behalf of those folks and our other co-organizers,
Wisconsin Public Television,
The Wisconsin Alumni Association,
and the UW-Madison Science Alliance,
thanks again for coming to Wednesday Nite at The Lab.
We do this every Wednesday night, 50 times a year.
Tonight it's my pleasure to introduce to you, Carsten Rott.
He's with the Wisconsin IceCube Particle Astrophysics Center
and was born in Hannover, Germany
and went to Gymnasium in Hannover,
and got his undergraduate degree
at the University of Hannover, Bachelor, or excuse me,
Master's Degree at Purdue University and his PhD at Purdue.
Of course I always have to point out that Purdue
is the French past participle for lost.
(laughter)
He also did for his work at Purdue,
he worked at the Fermilab,
which is the French participle for closed.
(laughter)
Then he went on to Penn State where he joined IceCube
and then went to Ohio State and then he's gone on to
creative university that he will pronounce for us.
And now he's back here at UW Madison on a sabbatical.
So I think he has covered four of the--
Are there 12 universities in the Big 10, 14?
14, that's why it's called the Big 10, Tom.
So I hope you're here to enjoying your time here in Madison.
The lake will freeze over in a couple of months.
You can go ice fishing.
His talk tonight is on dark matter,
"Don't Be Afraid of the Dark," and the cool thing is,
the folks that are doing dark matter research
are inviting us to consider October 31st every year
not just as Halloween, but as Dark Matter Day,
or as I would like to call it, Dark Matter Night.
And so I think it's great to have you here.
I know nothing about dark matter.
Let's let Carsten tell us all about it.
Please join me in welcoming Carsten Rott.
(applause)
- Okay, thank you for the nice introduction and
it's great to see such a large crowd here to come out,
to know what dark matter is.
And I think I have to disappoint you because
even after this talk, you will not know what dark matter is.
(laughter) And the reason is that we don't know yet
what dark matter is.
But the question about dark matter is actually
one of the most fundamental questions
that we are trying to answer.
So since the early ages of humanity,
people have been trying to answer the question
what is the world made out of?
And we have come a long way.
So nowadays we know that everything in this room,
pretty much, is made out of atoms.
So, and we can also, we know that the atoms,
we can decompose them in smaller particles
so they're made out of protons and neutrons and electrons.
And even if you use a particle accelerator,
you can break protons and you can find that protons
are actually made out of quarks,
which are the constituents that made up,
that make up neutrons and protons.
Now as we have built ever more powerful telescopes,
we also started to observe the universe and we wondered
what is the universe made out of?
Is the universe also made out of the same matter
that we have here, which we sometimes call
the ordinary matter?
So ordinary matter are the protons, neutrons and
electrons and everything that we know about.
So is the universe also made out of this ordinary matter?
Now as we observed the universe, we came along evidence
that actually the majority of matter in the universe
is not the ordinary matter that we know of,
but it's dark matter.
And that's actually why it is so important to answer
the question "What is this dark matter?"
Because in order to understand the universe,
and to answer the question,
"What is the world made out of?",
we have to understand what is dark matter.
And we have actually plenty of evidence for dark matter,
and I will, during this talk, explain to you
what, how do we know about dark matter,
what do we know about dark matter.
And then I will come to the question,
"How can we identify the properties of this dark matter?"
And since this series is called
Wednesday Nite at the Lab,
I've actually brought a picture of my lab,
which is the IceCube Neutrino Telescope,
located at the geographic South Pole,
and this is actually the laboratory that I work with,
I mean not at,
but I've been there a few times,
but that's only a few special occasions when
we get to go there.
And during this talk I will also explain you
why we can use the IceCube Neutrino Telescope
to look for dark matter and how we have
searched for dark matter with IceCube.
So now, let me begin with my talk
and let me give you the overview.
So this is basically what I'm gonna cover
during the next hour here,
so this is basically what I will suggest towards you.
So let's start with the first question,
"What do we know about dark matter?"
So we know from observations
that the mass energy content of the universe,
which is actually shown on the top right there,
that the universe is made out of roughly
five per cent ordinary matter,
so these are the protons, neutrons and electrons,
27 per cent dark matter,
and then 69 per cent dark energy.
And I'm not going to talk about dark energy today,
but that's also definitely a very interesting question.
So what we know about dark matter
is namely that dark matter could be a new particle
and basically all that we know
so far about dark matter
comes from the gravitational interaction that it has.
And maybe if you're a fan of Star Wars,
then you maybe remember this scene where Obi-Wan is
trying to find a missing planet in the star charts.
And basically he--
He finds that the gravitational pull
is pulling everything in this spot but there's no star.
So he concludes that, well,
if the gravitational pull is there,
then also a mass must be there.
And this kind of resembles also
what we know about dark matter.
We know, everything that we know about dark matter
comes basically from its gravitational interaction.
So let's go through some of the evidence
that we have for dark matter and
let's start with rotation curves
or reviewing, actually, the gravitational law.
So you can see the picture here of Isaac Newton
and his famous gravitational law,
which is shown here, which basically shows that
F, the force, that's exerted between two masses,
so in this case, the apple and the Earth,
is given by the two masses
and divided by the distanced squared
times a constant G, which is a gravitational constant.
So with this gravitational law, we can also,
we can basically describe all the phenomena
in our solar system and we can also
use this gravitational law to predict
how fast a planet has to move around the sun to stay
on a circular orbit, and this is actually the plot here
on the right side, and--
Yeah, so you can basically see that all the planets
follow this gravitational, or the prediction from the
gravitational law.
Maybe you think of Pluto,
that Pluto is not a planet anymore,
but of course, also the asteroids and everything else
or dwarf planets in our solar system
follow the same gravitational law.
Now, now we can actually ask,
"Is this gravitational law universally true?"
So if it works well in our solar system,
does it actually work well also to describe the motion
of stars in galaxies.
So on the bottom right, you see a picture of a galaxy,
so this is a large spiral galaxy,
and this galaxy consists out of billions of stars.
And in the middle you have basically
a large mass concentrations and the stars are moving
around this galactic center, basically.
And the question we want to ask well, are the stars
in the system following the gravitational law?
So some of the, or the pioneering work on this
actually has been done by Vera Rubin,
Rubin,
and she actually measured the
rotational velocities of stars in in galaxies.
She unfortunately passed away just about a year ago,
which it was very unfortunate because,
I mean, of course, it's very unfortunate,
but her, she did very, a lot of the pioneering work
on this and also found a lot of the
evidence for dark matter and she was also considered
for the Nobel Prize and in particular,
given that there are very few women who have won
the Nobel Prize it would have been nice if
she also received it.
So actually let's have a look at her work to honor her.
Now she tried to measure galactic rotation curves.
And to measure galactic rotation curves,
she used the Doppler Effect.
So we know the Doppler Effect basically
from everyday life when you have
a source of sound, for example.
So, let's take this firetruck here.
If the firetruck is moving towards you,
the sound pitch will change then
compared to when it's moving away from you.
And the same effect is actually present in light.
So we know that light is also waves,
and these waves actually get shifted,
if the source is moving away from us
or it's moving towards us.
And on the bottom here you can see an optical spectrum
and you can see some absorption lines in there.
And depending if the source is moving away or towards you,
you will see that these absorption lines are shifting.
And so basically if a source is moving away from you,
it shifts more towards the red
and if it's moving towards you, it shifts towards the blue.
So then on the right side you can see
that she looked at galaxies for which we had
basically an edge-on view and she then measured
basically the color or she actually looked at
specific spectral lines, so H-Alpha line,
from hydrogen and she then basically
could see how much the spectral lines are shifted.
So out of this then she can derive
what are actually the rotational velocities in this galaxy.
So this is a result that she found.
She actually looked at many different systems
but this is just one example.
So on the right side you can see
as function of the distance from this galactic center,
the rotational velocity of the gas and stars in the system.
And red is actually what you predict
based on the gravitational law.
And white is actually what she measured.
So you can see that this gravitational curve
actually stays pretty much flat.
Which basically indicates
that there's more matter there
than the luminous matter that we can see in this galaxy.
And she did this measurement actually for
many different galaxies, this is just some example of,
yeah, some of the measurements that she did.
So this is one case where we have found evidence
for additional matter that we cannot see.
There's also other evidence, for example,
through gravitational lensing.
So if you observe large clusters of galaxies,
as I've shown here, and in the back you might have--
You look at the distant galaxies behind that,
you can see that the image can be lensed.
And you can see this sort of--
Let me see, where is the pointer?
Okay, maybe it doesn't appear, but--
But you can sort of see this sort of ring shape,
and these are actually galaxies behind this galaxy cluster
and they get distorted and this distortion basically
is based on the bending of the light
due to the matter in between.
And then we can actually check how much matter
do we expect to be in between
and how much bending do we actually see?
And also from this you can derive
that there is additional matter.
Further evidence for dark matter and the,
actually one of its fundamental properties,
can be derived from an example
which is called the bullet cluster.
So this is actually a very beautiful image,
but it's actually a composite image
that is kind of false colors,
but let me just explain what you are seeing here.
So this is an example where two galaxy clusters,
so two clusters of galaxies are colliding
and they-- so they are collided and actually pass
through each other.
And what you can see on here in blue is actually
where the mass is distributed.
So this is actually from gravitational lensing,
you can obtain a distribution where the mass is located.
And the red you can actually see where the hot gas is.
So this is the ordinary matter.
So when these galaxy clusters collided,
actually a lot of the gas was stripped out
and this is left in between, while the--
most of the galaxies basically pass through each other.
And the matter is basically located
at this blue region.
Now this actually tells us something about dark matter.
Because we can see from this image that
dark matter did not collide with each other,
but just passed through each other.
So from this we can actually derive
this conclusion, at the bottom, that dark matter
does not interact very strongly with matter
and also not very strongly with itself.
Other evidence for dark matter...
comes actually from the structure in the universe.
You can actually see a movie up here which is
a simulation of our universe
and you can actually see
how the structure in the universe is forming.
So actually these
distributions basically shows the distribution
of the galaxies and matter in the universe
and you can see that you basically get these filaments.
So now-- Let me actually move on to the next slide.
I mean this actually goes on for quite a bit,
the simulation.
But if we actually look at the distribution of the galaxies
in our universe we can actually find a structure
that looks like this on the right.
And on the left actually I have put different simulations
of dark matter.
And I labeled these--
Well, I used different names: Cold, Warm and Hot Dark Matter.
So DM stands for dark matter here.
It actually describes how fast the dark matter particles
are moving, so for example,
if I think of a very fast- moving particle like a photon
or light, which moves with the speed of light,
then I would be in this regime of Hot Dark Matter.
And you see that the structure is very smeared out
which means that dark matter cannot be hot
and also cannot be warm but it's cold
and cold basically means that the dark matter
is moving very slowly or the dark matter particles
are moving very slowly.
Okay, so then there's further evidence for dark matter.
Actually from imprints to the cosmic microwave background,
maybe let me go quick on this.
So this is actually radiation that's emitted
at the very beginning of the universe and
this has been precisely measured actually
with the Planck satellite and from this
we can actually derive how much dark matter
there is in the universe.
Now let me move on.
So one of the last evidence that I want to mention here
for dark matter before I go to
how we search for dark matter
is actually evidence that comes from
the clusters of galaxies.
So in this image here, is the Coma Galaxy Cluster is shown.
So each of these objects here
is basically a galaxy and
we can also, again, using this method from Vera Rubin,
when she looks at the red shift or blue shift
of these objects, we can look at the velocity,
distribution of this object.
And if you assume there's more matter here
than the velocity distribution of these galaxies
will be increased, so they will be moving faster.
This is just basically what follows from gravity.
Now this is actually when, in the 1930s,
actually Fritz Zwicky, who was a famous astronomer
from Switzerland who worked most of the time at Cal Tech,
he actually observed this Coma Galaxy Cluster and he found
basically the first evidence for this
missing matter or how he called it, actually, dark matter,
or he spoke German so he said Dunkle Materie,
so the dark matter.
So this is a picture of him
and the Coma Cluster.
So since these early days of Zwicky actually we have
learned quite a lot about dark matter.
So there's conclusive, or there's overwhelming evidence
for dark matter on all scales in our universe
as I have shown you, but the big question is still,
what is this dark matter?
So we have seen dark matter
through its gravitational effect,
but we want to know what is this dark matter.
So let's go try to answer the question,
what is dark matter?
Now from these observational evidence that I showed you,
we can basically derive the following properties.
So dark matter is cold, which means it's,
relative, the particles are relatively slowly moving.
It's neutral which means it's not interacting through
electromagnetic interactions.
So it doesn't absorb or emit light,
because if it would emit light or absorb light
then we would have easily seen it.
And it's also not very strongly interacting
with the ordinary matter.
So this for example, we have seen in this example
of the bullet cluster, where the two galaxy clusters
are colliding.
And also there's this, this new particle has to be
stable because if it decays,
then it's not around anymore.
So these are basically the--
everything that we know about dark matter.
So then we can ask the question,
well, is there any particle that we know of
that has these properties?
So now here I show
a table of all the particles that we know of.
So this is actually the Standard Model of Particle Physics,
so this is basically what you can find
or what has been derived based on years and years of studies
at particle accelerators and colliders.
And these are all the particles that we know of.
And as you see on the top right,
the Higgs Boson this was basically the last missing particle
in this Standard Model of Particle Physics
and we think now that this is basically complete.
So we know all the particles that we have expected,
we have observed.
And we can ask the question,
well, is any particle in here,
does it have the properties of dark matter?
Well so first we have to ask the question
are those particles stable?
Or do they decay?
And we can cross out actually a lot of them
because most of them actually are very short-lived.
So you can only produce them at the collider
for a very short time and then they decay immediately.
Also we said that dark matter does not
emit or absorb light, so it's not what we say
electromagnetically interacting.
So we can ask, okay, which of these particles
are electromagnetically interacting
so we can cross those out.
So then with this, now we are only
with three particles left,
which are neutrinos but neutrinos are actually
relativistic particles,
so they move with the speed of light.
So also we said dark matter should not be relativistic,
because it should be cold.
So we can also cross these out and there's nothing left.
So the only conclusion that we can draw,
dark matter has to be a new particle, and--
Well, it's actually not so bad, I mean,
to have a new particle, it just enlarges our horizon,
maybe makes the world more interesting
if there is a new particle and there are actually
plenty of theoretical physicists who have cooked up
models that predict, for example, new particles and
just one of them is super symmetry which you
might have heard about but-- And people are looking for that.
But there are also many other theories
that predict new particles.
So now how can we actually look for this new particle?
There are basically
three different ways how we can search for dark matter.
The first one is we can try to produce dark matter.
So this is basically recreating the conditions that were
present at the very early universe when it was
very hot and dense, when we expect that dark matter
was actually created, so.
And we can do this actually at particle accelerator,
so this is, or collider.
So in this case we collide two particles with
very high energy and produce,
we can produce new particles.
The second way how we can look for dark matter
is actually through the scattering of
the dark matter particle with ordinary matter.
So this is the idea is basically like
you're playing pool,
if you have an atom and you have a dark matter particle
coming in, it could hit the atom in rare cases
and maybe give some nuclear recoil
and we can try to detect this interaction
of dark matter particles scattering on an atom.
And the last way we can look for dark matter,
what you call dark matter annihilations.
So when dark matter interact with each other,
it could produce maybe standard model particles
which we then can observe.
So now's let's have a quick look at these examples.
The first one, which we call Make It!
So the idea here is that we
use two standard model particles that we collide
at very high kinetic energies and then use
this energy to produce new particles.
Now this is being done at the Large Hadron Collider
at CERN, near Geneva, Switzerland.
And which is basically, yeah, 2.7,
27-ring circular accelerator in which we collide
two protons and these protons are basically
moving with the speed of light and are colliding
and when such a collision happens
this is basically shown on the top right here,
many particles are created and out of these many particles
that are created, we are trying to find a new particle.
And at the bottom right is, or bottom left,
is kind of such an example from kind of a theoretical
prediction for some new particles
that might be produced there.
So analyzing all this data is
incredibly difficult job
and these experiments, which is for example,
shown here, the CMS Detector,
there are really thousands of people working on this
and sorting through all this data.
And after sorting through all the data,
they have found basically no evidence for a new particle.
I mean, they have found the Higgs boson,
so there's something, but there is no dark matter,
or no physics beyond the standard model as we said.
Now the second way how we can look for dark matter
is to look for an interaction of dark matter
with ordinary matter and this is what I call here
Shake It!, so basically we shake the ordinary matter.
And actually outside here you can find
a booth actually by Kim Palladino,
so she's sitting over there,
and later on she can-- Since she's working on this
dark matter direct detection, she can later
also explain you more about this.
But here I just want to give you the basic idea.
So the basic idea is that this new particle
which I noted by this Greek letter Xx (chi) here,
is just hitting an ordinary atom
and depositing some energy.
We are trying to detect this small energy deposition.
This is incredibly difficult to do because
we know that dark matter is very rarely interacting
so to run these experiments you actually have to go
deep underground to be away from any background.
So yeah, later on please check out the booth outside.
Okay and then the last way,
and this is actually the way that
I mostly look for dark matter,
is through indirect searches for dark matter.
So in this case we assume that two dark matter particles
hit each other and in this process,
standard model particles are created
and those particles we then are trying to observe.
This is actually the basic idea here.
On the top left here you can see
these two dark matter particles, or we call this
WIMP dark matter here, weakly interacting massive particle,
are hitting each other and then are producing
some standard model particles and at the end
you go through some decay chains, but at the end
basically we can find stable particles
that we can observe like light, or,
yeah, neutrinos or some antimatter.
And there are different experiments that are trying to look
for this, or indirectly search for these signals.
Now let me-- I cannot go over all of them so let me just
pick the experiments that I'm working on,
which is the IceCube Neutrino Telescope.
So this is actually a picture taken at the South Pole,
so this is actually the counting house where
all our electronics are located for this experiment.
Now why have we constructed an experiment
at the South Pole?
Now, IceCube is a neutrino telescope and in order to
detect neutrinos we need to make
use of an effect which is called
"shrink of light," so this is actually
when a neutrino interacts
it produces some relativistic particles
which then send out some shrink of light.
And this is actually a picture of shrink of light.
This is actually taken in a nuclear reactor.
And in a nuclear reactor, you have also some
relativistic particles produced that pass through the water
and when they pass out through the water
they send out his shrink of light.
And basically we are trying to detect the same light
but when a neutrino interacts with the ice.
Now the--
Now in order to detect this light,
we need a detector medium that has very good
optical properties so that's why actually
we decided to build the detector at the South Pole.
Because we can, at the geographic South Pole,
the ice is roughly two miles thick
and has very good optical properties,
so that's why we decided to build a neutrino detector there.
So then the idea to detect neutrinos through
the shrink of light emission can be explained
in this following cartoon here.
So you have a neutrino and that's coming in
on the bottom right here, it's interacting,
producing a particle which I call a muon here.
And this muon is basically like a heavy electron.
And when these neutrinos interact,
in particular high energy neutrino,
it produces a very energetic muon and this muon
can actually travel several miles.
And when it travels through the ice it sends out
a cone of this shrink of light
so all that we need now is a
precisely-timed optical sensor array
and with this precisely- timed optical sensor array
we can then detect this shrink of light
and reconstruct where the neutrino came from.
Now this is a simulation here
that actually shows this effect.
So this, what you can see here are different strings,
different strings of optical sensor modules
and this, an energetic muon passing through this detector.
Let me actually show this again.
And as it passes through the detector,
you see this shrink of light that's emitted
and whenever this light gets detected by one of the
optical sensor modules we mark this by one of these
colored balls here which basically indicates
the time actually when the optical module was hit.
And the size of these blobs basically indicate
how much light was detected.
Now this IceCube Neutrino Telescope is actually a
multipurpose experiment.
It basically serves many different
science or physics cases
and basically we are trying to look for neutrinos
of astrophysical origin.
We're trying to study cosmic rays,
atmospheric neutrinos,
even glaciology, trying to understand the ice
and also look for dark matter.
And of course, IceCube is headquartered here
at UW-Madison, so maybe some of you know already
a bit about it, so it's very exciting experiment.
And it's actually a very large international collaboration.
Also so there are about 300 people working on the experiment
from all around the world.
From 12 different countries
and all the countries are shown here.
This is actually a picture of the
South Pole where our experiment is located.
This is actually the South Pole marker.
This marker actually stands where the
geographic South Pole is and you can--
If you read on there, you can actually read this
January 1st, 2008, so this is actually
at the time when I was there, so I took that picture.
This is actually, some image of me there.
So at that time, the gray in the beard
is actually frost, (laughter)
but now it became real so time has passed on, so.
Okay so then the detector
is located very close to the geographic South Pole.
You can see basically on the top right there,
a map of Antarctica and where the geographic South Pole
is located and on the--
Yeah, basically you can see there where the
geographic South Pole is and also
where the Amundsen-Scott South Pole Station is.
So this is actually where the scientists live.
Then there's a Skiway, this is actually where we
used to, where planes come in to bring in supplies
and scientists to work there.
And then very close to this
station is actually where the IceCube Neutrino Telescope
is located.
And on the top left you can see actually
a temperature chart and I haven't
seen any winters here in Madison yet, but I hear that
during this time here in November, December,
we go to yeah, maybe minus 30 degrees at the South Pole
so maybe we'll reach this temperature here also.
But you can see from this temperature profile then in
the austral summer, or austral winter period actually
goes down to minus 70 or so, or even below that.
And the IceCube detector was actually constructed
during this period from November to February,
so that's actually when the South Pole is accessible.
So after that, the station basically
is not accessible and only a few people
stay behind to keep the detector running.
This was actually, on this picture here,
the guy in the middle, tech,
he was actually one of our Winterovers who stayed there
one entire year to keep the detector running,
so they are doing a tremendous job, actually.
Okay, so on the, yeah,
bottom right you can see kind of this footprint where the
IceCube Neutrino Telescope is located.
Now let's actually go below the surface
to see how the detector looks like.
And you can see here
in the schematic view how the detector looks like.
So first of all, the ice is roughly
three kilometers deep and
we have used a hot water drill to drill holes
into this ice to a depth of 2.5 kilometers
and then deployed optical sensor modules.
So in the bottom right you can see actually
such an optical sensor module.
So it's basically, kind of this basketball-sized module
that contains a PMT or photomultiplier
to basically a large light sensor,
and with that, we want to detect the light
from the neutrinos that are interacting in the ice.
Then this detector was built over a period
of seven years and has been taking data
since 2011, ever since.
Actually already during the construction period
we obtained many very useful science data.
Okay.
This is how the detector
would look like if you could
float through the ice.
These are actually the optical sensor modules.
So it's basically at the bottom you can see this
large optical or this large
PMT and then also the top,
it's basically just some electronics
that digitizes the signal that's received
by this optical sensor module.
Okay, so then how do we look for dark matter
with this neutrino telescope?
Well one of the most spectacular ways
actually how to look for dark matter
with IceCube or very unique ways
is actually to look for dark matter that's captured
in the sun.
This is actually-- It sounds at the beginning,
quite out of this world that this would be possible
but it's actually a very reliable way
to look for dark matter.
And the idea is here that you have
dark matter particles from the galactic dark matter halo,
so as we said earlier, the galaxies are engulfed
in dark matter and so these individual particles
could scatter eventually
on or with the hydrogen atom in the sun.
When this scattering happens,
they can lose some energy and they can become
gravitationally bound to the sun.
And this is basically what's shown here in this pink line.
So you have a particle that's bound to
the sun and, or this dark matter particle and it will
maybe this orbit brings it through the sun
and it has a higher chance of interacting again.
It will lose more energy and eventually sink
to the center of the sun.
So if this process happens over millions of years,
we basically accumulate in the center of the sun
dark matter.
And when you have an enriched region of dark matter,
eventually it will also interact with each other
and when it interacts, it can produce the
standard model particles.
Now from all these particles that are produced
in the center of the sun,
they are basically no particles that could make it out,
only neutrinos, are the only particles that can
make it out of the sun.
So neutrino, I should have also mentioned
also called the Ghost Particles because they
interact so rarely, so they can make it out of the sun
and then come to the Earth.
And if we detect such a neutrino with the
IceCube Detector and see that the signal points back
to the center of the sun, then this is a
smoking gun signal for dark matter.
Now we have performed such a search,
actually several searches.
This is actually some results from the scientific
papers that we have written on this.
Basically on the bottom left, you can see
we are basically counting the number of neutrinos
that we observe in direction of the sun.
And this is actually what's shown in these black dots here
and this gray band is actually,
maybe just look at one of the--
yeah, one of this bottom region here, so.
And this gray band is actually what
we expect from a background from
neutrinos that are naturally produced
in the Earth's atmosphere.
And you can see that this gray band which is kind of
the natural background
is basically flat and the dots that we observe
are pretty much just scattered
around it which means we don't see any excess
of events or any additional neutrinos coming
from the center of the sun,
so which is unfortunate, which means we have not
seen any dark matter that's captured in the sun.
Otherwise, also if we would have seen it,
for sure you would have heard about it already so. (laughter)
And then on the bottom right,
is actually the results plot,
so this actually shows,
and on the X axis, so on the horizontal axis,
you have the math of the dark matter particle
and on the vertical axis is basically the
interaction cross-section or how strong this
dark matter particle would interact with ordinary matter.
And, this red line at the bottom,
this is actually the result from the
IceCube Neutrino Telescope, so it actually shows
that the IceCube results are very relevant.
So also on there are shown some other experiments
and you can see that IceCube actually has some of the
strongest bounds on dark matter,
so we have not found dark matter, but we can still
exclude some parameters space, which is then important
for theorists, who are creating models for dark matter.
To know kind of where there is no dark matter.
So these searches are actually very important.
There are many other ways also of how we have searched
for, indirectly for dark matter.
So we have looked for dark matter annihilation
in our galaxy, in the galactic center,
in small galaxies, in galaxy clusters.
In all those we have not found any,
any evidence for dark matter.
And similar, also other observatories observing
with gamma rays, they have not found any,
any evidence for dark matter.
Now one of the things
that we have, however,
seen with IceCube recently is we observed
very high-energy neutrinos.
This is actually following this and also the
completion of the IceCube Neutrino Telescope,
we have also won this Breakthrough of the Year
from Physics World and this is actually a very
big or important discovery because for the first time
we have observed energetic neutrinos from,
yeah from, of extraterrestrial origin.
So they are from somewhere from outer space.
And we still don't know where these neutrinos
are coming from.
So these neutrinos have humongous energies.
So they actually have energies much higher
than the energies that are created, for example,
at the LHC, at the particle accelerator.
Basically a thousand times higher in energy
are these neutrinos
or some of the neutrinos that we have observed.
And the big question is
where are these neutrinos coming from?
So there are some natural astrophysical sources,
source candidates like gamma ray bursts,
active galactic nuclei.
But also people have suggested maybe
there's some new physics.
So it could also be, and so we are also looking if
these high energy neutrino flux has any
exotic origin or origin from dark matter so.
Okay so, with that, actually I'm come to the end
and so let me conclude.
So first of all,
we know that most of the universe is
made out of dark matter.
So there's overwhelming evidence for the existence
of dark matter and I've showed you at the beginning
of this talk the different ways how we have found
the evidence for the existence of dark matter.
So for example in large scale structure of the universe,
the galactic rotation curves,
through gravitational lensing,
cosmic microwave background and so on.
So there's overwhelming evidence for the existence
of dark matter on all scales in the universe.
And we tend to believe that this dark matter
is a new type of matter that we have--
Yeah, a new type of matter and we have found
or we have identified certain properties of it.
So it has to be stable, it's non-barionic,
not very strongly interacting and it's also not
absorbing or emitting light and yeah.
It's stable and not decaying.
And to understand the universe, really,
we have to understand or we have to learn
what dark matter is and that's why it's such important,
such, yeah, that's why it's so important to look
for dark matter and all these--
They're intensive efforts now ongoing,
by searches at particle accelerators
indirectly through looking for the annihilation of
dark matter and directly looking for the scattering
of dark matter with nuclei
and with, through all these searches we have--
We were able to already exclude some of the models
that have been proposed to explain dark matter
but there's still plenty of parameter space out there
to explore and really we have to find dark matter
to understand the universe and to answer the most,
one of our most fundamental questions,
what is the world made out of?
And so I hope you enjoyed this talk and also
please remember October 31st, Halloween, no.
No, it's Dark Matter Day, so that time
you can learn more about dark matter so.
Thank you for your attention.
(applause)