University Place  Paolo Desiati The Science of Ice Cube: Beyond Neutrinos  UP939 October 30, 2013   cc >> Welcome, everyone, to 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, and it's another opportunity for you to share in the discovery here at your public land-grant research university. Tonight, it's a delight for me to be able to introduce to you my friend Paolo Desiati, who will be talking to us about the science of IceCube, going way beyond neutrinos even to things like Earth tomotography. Tomography. Sometimes I put too many Ts in. Paolo started in 1993, did a one-year undergraduate research in the underground. He's an underground person. 

He worked at the Gran Sasso Underground National Laboratory in Italy, and that's where he started working on cosmic ray experiments. In 1994, he got his master's degree in physics at the University of Florence in Italy, which is where he grew up. In 1999, he got his PhD in physics at the University of Rome La Sapienza. He did his PhD on the NESTOR neutrino telescope project in the Mediterranean. And then from 1999 to 2001, he was a postdoctoral researcher with the -- in Germany. He worked on the AMANDA Neutrino Observatory, which was the precursor to the IceCube. And AMANDA is at the South Pole, is that correct? And then since 2001, he's been an associate scientist at the Wisconsin IceCube Particle and Astrophysics Center, and he's also an associate scientist with the Department of Astronomy here at UW-Madison. It's pretty interesting to see the parallels between something going on in 1609 and 1610 with the telescope and the things that are going on in our lifetime at the South Pole with one of the world's largest scientific apparatuses ever built. It's so large, as a matter of fact, it seems that they weren't even aware of all the things they could do with it, which I think is what Paolo is going to get to tell us about tonight. Please join me in welcoming Paolo Desiati to Wednesday Nite at the Lab. 

[APPLAUSE]  >> Thank you very much. Can you hear me? So it's a lot of you tonight, and I have to apologize for my voice. It might be a little low tonight. So, the title might be maybe a little surprising for a few of us. I was saying earlier that when I take a taxicab to go to the airport, everybody knows about IceCube, sometimes more than I do I think. There's a lot of outreach about this big project at the University of Wisconsin. It's an astrophysics project, and it's built at the South Pole. I will talk about it. It's a very weird and strange type of observatory. And it's main purpose is to do astrophysics. 

And what type of astrophysics I will to describe to you. But what I want to describe also, and that's the second story, is that IceCube, which is an instrument built for a specific topic, can actually be used to do very interesting interdisciplinary science. Some of them it's not very advanced, it's just the beginning, like Earth tomography, but I think it's very interesting to show you what potential this instrument has besides astrophysics. So, and the third story, of course, since the IceCube is at the South Pole in the Antarctic, I want to show you a few pictures of that place. What it means to live there sometimes for a few weeks, to work there, and I think it's very interesting to see that. So three stories. Everything started in the beginning of the 20th century. A lot of science developed there. Modern science basically has its root in many aspects in that time. And there are only three people who contributed to what today we call cosmic rays. 

And those were the years where radioactivity was discovered, and people were studying radioactivity. And radioactivity was, the idea was radioactivity is producing the Earth. There are some materials that transform themselves from one --, one atomic strapped to another, and then this transformation emits some radiation. And people were eager to study this radiation. So various scientists at the time, they built instruments like -- to measure this radioactivity, and they wanted to see whether there is a difference between radioactivity at the surface of the Earth and in altitude. So what he did, he went to Paris, he went on the top of the Eiffel Tower, and he measured that radioactivity decreases enough but not as much as he thought. So he, for the first time, he had the idea that perhaps there is some radioactivity coming from the sky besides from the Earth. -- from Italy, he did the opposite. He actually took a military submarine, put an instrument inside, and went below the sea surface and found out that radioactivity depends on the seasonal temperature of the atmosphere. So he had also -- that somehow the atmosphere is related to the radioactivity that is measured on Earth. 

But everybody says that the discovery of cosmic rays, or the click in the brain, happened when Victor Francis Hess, this Austrian scientist, took a balloon and put his instrument on the balloon and it went very high and he demonstrated that radioactivity does not decrease with altitude, but actually it increases. So there is definitely a source of radioactivity coming from the sky. That was a very profound, had a very profound effect on scientists. Nobody had any idea what that meant. Basically, even today we don't really have any idea, but we know much more than those days. So, basically, cosmic rays are these massive particles, basically particles that we know. They are protons, they are nuclei of helium, of carbon, of nitrogen. We have these materials everywhere on Earth. They have been stripped of the electrons that usually orbit around the nuclei, and they travel in space. Where they come from we don't know. 

And the origin of their energy is basically unknown. When they heat once in a while, Earth, they basically cannot then heat nitrogen and oxygen atoms in the atmosphere, and they produce this cascading interactions. And then usually cosmic rays are measured directly with satellite, usually very small experiments that orbit around the Earth. So they measure directly the particles coming from the sky. Or balloons that are, they travel very high in the upper atmosphere, not exactly in space, so they can still detect cosmic rays. But if you want to detect cosmic rays at much higher energies since they are much rarer, the rate of the cosmic rays the higher the energy is lower, we usually build instruments on the surface of the Earth, and when we build an instrument on the surface of the Earth, it's impossible to measure direct the cosmic rays, but we measure their effects. All the secondary particles. Among them there are neutrinos, which I'm talking about later. So, what I'm trying to explain is what cosmic rays are, where do they come from, and what they are telling us. I'm not giving you the solution because actually we do not know. 

We actually know what cosmic rays are definitely, but we don't know where they come from, and we don't know what they are telling us. What I'm going to say, though, is that we can study cosmic rays in many different indirect ways, through gamma ray detection, and I will talk about this a little bit, and neutrino, which is what IceCube is doing. First of all, let me go to the South Pole. This is where we do the science. The South Pole is a very particular place on Earth. It's in the middle of the Antarctic Continent, which is this vast continent of ice, and I like to call it the bottom of the world. And it's very close, the South Pole station is surrounded by scientific instrumentation, many types. You can see the South Pole Telescope, which is studying, basically, the origin of the universe. They observe the sky, and they observe the background radiation that is emitted by the universe as an echo of the beginning of the universe's life. And many things are happening around. 

And so I want to show you what a little bit of the place where we do the science. For example, if from the United States we want to go to the Pole, we have to go to LA, travel, perhaps for 14 hours, to Auckland, New Zealand, and then just one hour to Christchurch, which is in the south of New Zealand, and if the weather is good, which might happen one or two weeks later, with National Guard planes, usually C130 or some other planes, we travel six hours down to McMurdo Station, which is a logistic station. It's a city, basically. It's a town at the coast. It's actually on an island offshore of the continent. And then three hours fly to the South Pole. But when I went to the South Pole a few years ago, I was traveling from Europe. I was a postdoc in Germany, and since I've been in Madison, actually never went to the Pole again. Although, here it's actually as cold as there in summer, in winter. So I was flying from Frankfurt to Singapore to Christchurch, and then the same trip. 

It was a big enough trip. Once we got in Christchurch, we go to the CDC, the  Clothing Distribution Center, and they show you... [LAUGHTER] The clothes you actually do need. Sometimes they give you a choice between different gloves or hat, but the more you can get with you, the better because it's really cold and many layers is actually the best you can do. And so definitely the must is the red parka, which is the most beautiful tool out there. It's amazing. I wanted to get one of those when I was coming to Madison, but honestly even though here it's really cold, most of the time this is too warm. So we can't use it. Or boots or gloves, many layers of gloves, many layers of socks and pants. And then you put them in orange bags, usually two of them. 

Pretty thick. Like military people. And then we, I don't think this is a C130, but typically we board on cargo planes. And usually most of the time we are on the side of the plane, no windows, extremely noisy so we have to use earplugs. And in front of your face, just one meter away, you can have onions, potatoes, chocolate, or mechanic instrumentation, these sorts of things. Or, if you're lucky, you can have the entire cargo space for you to have these beautiful seats. It never happened to me unfortunately. [LAUGHTER] So then we arrive at McMurdo, and usually the airport in McMurdo is actually on the ice shelf. It's not in the continent. And the ice is very thick. 

And depending on the season, the airport can be just in front of the town of McMurdo or when in general the first icebreaker comes and breaks the ice so then the airport is moved much farther away. So there are two possible sides. And it's a beautiful place. There's this fantastic volcano, Mount Erebus, which is on Ross Island, and it's a remarkable place full of life, animals, and it's a beautiful scene to stay there. Then we take another C130, and if you're lucky to get in the cockpit or to watch from one of these little windows, you can see Antarctic mountain chain, which is spectacular, and then after three hours you land at the South Pole, which is really stunning psychologically, but from a natural point of view it's not as beautiful as McMurdo because it's just white flatness on a blue sky. No animals, no life. Only humans doing strange science. So the plane just, this is a C130, just lands on this runway on skis, not on wheels, although the skis can be taken away, and then between the station and the scientific location depending where you are, we just go back and forth and sometimes the weather is not very nice. Well, when I was there in 2000-2001, the South Pole station was this very interesting dome which, over the years, had been submerged by ice. So the surface of the South Pole because of drift due to the wind just gets higher and higher. 

So at that time I know to get into the dome, they had to excavate this tunnel. And then inside is little, looks like marzipan or gingerbread houses, and we were working there. But nowadays there is a grand hotel station which is this wonderful piece of architecture built at the South Pole. And, of course, you go to the galley to eat, some colleagues play golf with a red ball because otherwise you don't see it, and then you have to do your shift to clean the dishes. And every January 1st there is the race around the world, three miles. [LAUGHTER] Around the world. And this is 3,000 meters above the sea level, the oxygen is pretty thin. So you have to be really in good shape to do that. Okay, so that's a little bit of a background where actually people work during the summer and some of them do the entire winter in order to make sure that instrumentation work and everything goes right. So, how do we investigate down there the origin of the cosmic rays? So, let me go a little bit back. 

Since the beginning, actually since the 1700s, scientists have investigated the electromagnetic spectrum. So with our eyes, we can see only a little, a tiny little bit of the electromagnetic spectrum, which is the visible light. We can see from the deep red infrared light to the ultraviolet light, but this is just a tiny little interval of the possibilities the electromagnetic spectrum can have. It's still the same particle as photons, it's just light photons. A photon is a particle without any mass. They travel along in space at the speed of light, and they are categorized by a frequency of oscillation. The frequency of oscillation of visible light is very narrow, as I said, but the frequency can vary enormously from radio waves to microwaves, infrared, ultraviolet, X-rays, and gamma rays. And the different frequency of electromagnetic spectrum have connections to different physics processes. And in the every day life we know if you have a broken bone, you go to the hospital and they use X-rays because X-rays can penetrate what we cannot see. And then it's absorbed by thicker tissues like bones. 

So you can see the structure of the bones. Or you can actually have an infrared measure of your hand where the heated surface produces more infrared light than cold surfaces. So you can actually visualize temperature gradient between different parts of objects. And the same we do in science. We observe the same object, in this case it's a supernova remnant, which is what remains of an explosion of a star many years ago, in different frequencies. And each frequency tells us a different story. What temperature it is. What particles actually are emitted there. What magnetic field is in there. So this is an extraordinary way to do astronomy and astrophysics which goes beyond optical observation of traditional astronomy. 

So these are just two examples of two objects. The Crab Nebula, which I've showed before in X-ray and infrared. This are actually pictures taken of a time, so they've been put together in a movie. So things actually change, even in space, over time. And the longer the observation, the more we can see how they change. Or we can look at another supernova remnant, which is Vela supernova remnant which is basically almost invisible in optical light. We can't really see very well. But in X-rays it's as large as five degrees. Just to give you an idea, the moon and the sun are only half a degree. So if we had X-ray vision, the sky would be extraordinarily different. 

For example, this one. You can see the third to last is the optical view of the galactic center. If you go to a very dark place, you can see the Milky Way, the galactic plane, crossing the sky. If we had vision in other frequencies, like X-ray down there, it would look completely different. And gamma rays even more than in radio frequencies. So the galaxy looks completely different, and each of these pictures tell us a different story. For example, where cosmic rays are generated inside the galaxy. What is missing here is a neutrino sky map, which is what IceCube will do. It's actually starting to do it. So, what is the connection between neutrino and the high energy photons, gamma rays basically, and cosmic rays? So, these are what we call the messengers of the cosmos. 

They come from somewhere, we don't know exactly where, and they have information about the origin of the cosmic rays. So, for example, gamma rays, which are these very high energetic lights that we cannot see with our eyes, we need special instrumentation, they are produced in objects within our galaxy, or even outside of the galaxy, by star explosion or by mechanism that accelerate protons and carbons and nitrogens on nuclei. And the same mechanisms that produce these high energy photons, they have to produce neutrinos. We know that because this happens exactly on Earth. If you go to Fermilab or you go to CERN, this is exactly what happens. There is no reason to think that physics somewhere else is different than here. Unless, really, we are missing the fundamental point in nature. But there is no reason. So what we observe here, it has to be observed somewhere else. We know that if a proton interacts with some target, it produces a lot of different particles. 

Some of them are neutrinos, and some of them are photons. So the same thing must happen in the sky. The problem is that the sky is not like an accelerator where everything is control. You have a proton beam with a specific energy, specific direction and the target well determined, here everything is not very well known. So astrophysics is the differences between astronomy that tells us what is out there and particle physics which is what accelerators tell us. And neutrino come into play because neutrino have to be produced by the same processes that produce high energy gamma rays, but there is less ambiguity. These neutrinos are only associated to the acceleration of cosmic rays. They're the reason why we observe very high energy cosmic rays in the sky, which is a mystery. There is so much energy out there we don't know where it comes from. So what happens when this cosmic ray's proton, for example, hits the Earth? Of course, the reason why the line is so wiggly here is because cosmic rays have a charge and the sky out there, within the galaxy and between galaxies, have a magnetic field. 

Magnetic field in charged particle, they don't, charged particles might have to change directions. So we cannot point back when we detect cosmic rays. They just come randomly from any direction because the magnetic field has totally scrambled them. But photons and neutrinos don't have a charge. They don't know anything about magnetic fields. They don't know anything about a material between us and the source, mainly, especially for neutrinos. But the problem of neutrinos is that the same reason why it makes them these very good messengers of processes very far away from us, it makes them very difficult to detect. We need huge detectors because neutrinos don't really like to mess up normal matter. That's the particularity of these particles. And this is why neutrinos are, in many aspects, still very mysterious. 

They don't like to interact very much with matter. They're very rare processes. But cosmic rays are not very rare. These are protons. We know them. Again, we just don't know where they come from. But when they hit the atmosphere, they just produce a lot of secondary particles. We know all of them because they are producing accelerators, so we use this cascading processes in the atmosphere that ultimately will produce some neutrinos, which we call atmospheric neutrinos, which we have to distinguish from the neutrinos that eventually are produced in very far away sources, the same sources of the cosmic rays. These are our background. We have to understand, with the help of particle physics that explain us these processes, but we have eliminate them in our observation because we want to detect neutrinos coming from outside of the Earth not in the atmosphere. 

And one way to do that is to build an upside down telescope. Usually a traditional telescope is a dome. A telescope is usual optical but not all the antennas, radio telescopes looking up the sky and you observe the sky. In this case, you observe many of the sky from the below. And below is actually the Earth. The reason why we do that is because cosmic rays like this that hit the atmosphere will produce a lot of neutrinos that usually are a kind of disturbance for us. But also muons. This Greek letter mu means that these are really particles like electrons. Electrons are the particle that produce electricity in copper wires. And the difference between muon and electrons is muons can propagate in rock and the Earth for like 10-20 kilometers. 

So if you build a detector two kilometer below the ice of the rock, you can see a lot of these muons. Usually one million every neutrino. So you'll want to observe the sky from below where there is no muon coming from outside the Earth because they have been absorbed by the Earth but the Earth is not able to absorb neutrinos. So usually we look down, and if there is an event, a particle coming from the center of the Earth up, this is definitely produced by neutrinos that have interacted near by the detector. It's a completely different concept which actually was theorized already in the '30s and '40s, and finally it has been built.  So, once a neutrino coming from below interacts, and this happens once in a million times, a million neutrino come through, one of them interact nearby the detector, it produces a mu, for example. We know mus can propagate for a very long distance within the ice. The ice is transparent. There is a phenomenon, there is an effect called Cherenkov effect that if you have a particle, a very energetic particle at very high speed propagating a transparent medium, a light is produced which is called Cherenkov light. This is the same or a very similar phenomenon which happens on a supersonic plane when a plane is very fast, and it's must faster than the speed of sound in the air. 

You have this wake produced at a specific angle. In this case, this visible wake is due to the condensation of the air because of a high pressure. But in particle physics, this is due to the fact that the particle ionizes and interacts with the atoms of the ice and produces this light at a specific angle. The same thing, I don't know if you can see, happens if you happen to go to a nuclear plant and see where the reactor is, all the electron or whatever secondary particle produced by the radiation of the fuel of the nuclear plant produced Cherenkov light, which is in the blue. Although, the peak of the light is in the ultraviolet that we cannot see without ice. So that's a concept, an upside telescope, basically, to detect neutrinos. And what we did, we actually  built one at the South Pole. And IceCube, that's the name of the observatory, it consists, it's a very simple detector. It is not as complicated as those built at Fermilab nearby here or at CERN. It is not as complicated, but it's very simple and it's gigantic. 

You can see the Eiffel Tower, which is 300 meters high, is actually only one-third or less than a third of the height of the detector. So we built them, we built IceCube under the ice at the South Pole at some depth. The ice is actually three kilometers thick. So we built the detector between 1500 and 2500 meters. And in each of these what we call string, vertical string, we put a number of sensors which are enclosed in a glass sphere. And these sensors are basically the opposite of a lamp. A lamp usually produces light and then emits light. What these do are actually detect light, and they are so sensitive they can detect a single photon, and our eye, for example, is not able to distinguish a second photon from some noise due to our nervous system. These are extremely sensitive. The photons produced by the Cherenkov light of the muons can be detected by these inverse lamps. 

And then on the upper side of this lamp, which is usually looking down because we want to detect neutrinos coming from below, there is all this electronic board which is a better position by itself. So the signal detected by this inverse lamp is digitized and then sent up to the surface. Each of the strings which contains 60 of these sensors have a distance of 125 meters. So the entire volume of detector is actually one kilometer long and one kilometer wide. It's a huge volume, and it's very hard to visualize because 125 meters apart, the distance between the strings or the cables, is actually very long. And each of these spheres is only like this. So it's a very sparse detector. Huge volume. So the way we built the holes is a very fancy drill system that goes in two stages. One is a heater that produces a hole in what we call the firn, which is 200 meters of non-compacted ice. 

It's basically snow. And after 200 meters, the pressure is so high that the snow crystallizes so it's really solid. And then a second drill shoots a high pressure, high temperature water to produce to actually create the hole which is almost 3,000 meters long and 60 centimeters wide. And this process is done in less than a day. But since when I was going there I was still working AMANDA, I like to compare the two ages. The drill -- in AMANDA was something like, I don't know, a huge mess. And then there were these huge heaters producing hot water, and to drill a hole 25, AMANDA was shallower, 22 kilometers or 2500 meters, it took like five days. So it had to be done in different stages because there was no way to build in one single shot such a long hole. But in IceCube, the drill system has a huge power compared to AMANDA. Everything can be done in one single day, actually 20 hours I think. 

And once the hole is done, the drill camp, the drillers go away, and we go there, we arrive there. In AMANDA we used to mount these tents around the hole with a tower that is used to take cable where we mount the different optical models. And it was very cold down there. There was this heater with hot air, which is like a beam. Everything there is extremely cold. You have to be there. So everybody was a long the beam of the heat here. And a person which was the farthest way, they don't like it. It was pretty intense. But now there is this very fancy hut. 

Everything is super organized. Even a deployment of the spheres is actually extremely fast compared to AMANDA time. So, I hope this move is not going to stuck my computer because it's huge. So this is actually what happens. So, basically, there are two types of neutrinos. One is a neutrino that produces what we call a cascade. It's a neutrino electron neutrino that produces an electron instead of a muon. Electron cannot propagate a very long time in ice, so the Cherenkov light produced by this particle that don't propagate very far actually appears to ask when this gigantic volume has a sphere. And what you're visualizing here is individual photons from the Cherenkov radiation that crosses, propagates through the ice and then is scattered in the ice and doesn't go straight. And the color goes from red is the prompt photons that arrive early, and blue are the ones that arrive later. 

And the optical sensor, as I showed you before this inverse lamp, they detect these photons and we represent their detection in this way down here, in the bottom left, where the size of the bowls represent how many photons we have detected and the color, how early. Red is very early, and blue is very late. In this case, photons propagate on one central point outward. But neutrinos can also be of type muon. So when they interact in matter, they produce the muon. Muon, unlike the electron, can actually propagate several kilometers in the ice. So it looks like a track. This is what we call track-like events. They're associated with neutrinos if they come from below or from the horizon. And, again, the photons propagate in this cone-like fashion, and they propagate outward and they scatter in the ice and they eventually will make the photons more diffuse. 

And the way they look like in the detector is that optical modules along the trajectory of one kilometer long pathway of the particle illuminate and give us the time and how many photons. In this case especially, it's easier, we take all these data, actually I should say this later. So, basically, I already show this, so an event crosses the detector, the data are sent on the surface, and then the digitized data from each of the optical spheres, and then they are collected by this amazing set of cables and stored on disc. And we have an online processing of the data. We constructed direction based on the time and the number of photons, and then we can build sky maps like this. So this sky map says a little bit more than I said. So you can see the Earth up there. So we are at the South Pole. So we are located upside down over the South Pole, and we detect neutrinos basically from below because from above are dominated by radio produced by cosmic ray interaction. We want to detect neutrinos that are for sure neutrinos and not muons. 

So basically the upper sphere here, this is basically the sky opening up in an ellipse way. So each of these dots is a reconstructed direction of a neutrino. And the one coming from above the upper one are the neutrinos that have crossed the Earth can come up. Belong, instead, these are dominated by the muons, not neutrinos. But we take the sky map, of course by eye it looks like there's really nothing interesting. These are all atmosphere events connected to cosmic ray interaction in the atmosphere not to the origin of the cosmic rays. But perhaps between them, there are neutrinos that have been produced very far away and they sneaked into the atmospheric originated radioaction. One way to do that is to study statistically whether there are clusters of this, especially the high energies. And in a sky map like this, I have to say we didn't see any specific clusters. So this is interesting but in a different way. 

No evidence of astrophysical neutrinos from this map. But this is interesting because then we build up sky maps of probabilities of clusters of neutrinos. We take all these events, the direction, and we calculate what is the probability that one or more neutrinos are clustered within a specific angle. And this is the, we built a colored map. The red color means high probability of clustering, and blue color means low. And we compare that with the gamma ray observations which, as you can see, probably, I don't know, it's not dark enough, they're extremely detailed. And that tells you how easy it is to detect high energy gamma rays and how complicated it is to detect neutrinos. Huge statistics of gamma rays, very fine structures everywhere. You can see gamma rays produced by sources in the galaxy, and outside of the galaxy we still are struggling in collecting as many events as possible. But then, and this is the end of my neutrino part, there are different ways of detecting neutrinos. 

One way is we want to see neutrinos that interact inside the detector and are as bright as possible. Well, we found two in the last three years of data taken by IceCube, and they are so remarkably energetic and huge we gave them names: Bert and Ernie. [LAUGHTER] Actually, a student, these were found by a student in Japan. They are studying the data of IceCube to look for extremely high energy neutrinos, and these were the lowest energy neutrinos in their analysis. So they didn't find anything above this high energy, but we found two. Just to give you the idea of how large these events are inside the volume of IceCube, you see Camp Randall I think is 200 meters long. Sorry, I don't know exactly the feet. So, basically, the extension of the event is twice the size of Randall. Several blocks in Madison. So it's a huge extension. 

And consider the detector is one kilometer cubed. These are actually interesting. There are two of them, and they are not track-like, as I showed you before. The direction is defined but not as well as you can find the direction from a specific elongated track but have very high energy. And they are very unlikely to be produced in the atmosphere. So maybe this is really the first time that we are seeing extraterrestrial neutrinos. Although, we have no idea, actually, what they are. So the two neutrinos, Bert and Ernie, if you look at their energy, are actually the total photons that have been detected by our optical sensors, which is an indication of how much energy there. They're up there in the red circle over there. And you see they're well above the expectation of neutrinos emitted in the atmosphere by being part of cosmic rays. 

So something interesting is happening there. So maybe this is the beginning of neutrino astrophysics. But the thing is that we don't really know. It's very exciting for us. This is really fantastic. It's very good news for our project, but the only thing we have to do now is to wait for more data and see what actually happens. We do expect extraterrestrial neutrino to be much more energetic; therefore, when the atmospheric neutrino at high energy become rarer, we would expect high neutrinos from the origin of the cosmic rays to sneak out exactly as we are maybe starting to see. So, I want to show you this. Sorry. So there will be an event about neutrinos about all this and perhaps the beginning of a neutrino astrophysics in Milwaukee. 

So I was asked to show you this one-minute and 20-second movie. It is a promo of this event at the Milwaukee Public Museum.  >> Deep in the ice at the heart of Antarctica, the biggest and strangest detector in the world waits for mysterious messengers from the cosmos.  See how the IceCube Telescope chases ghostly particles called neutrinos. These tiny but extremely energetic particles give us new ways to explore the most amazing places in space.  Exploding stars around black holes. Neutrinos are helping us answer some of the biggest mysteries in our universe. Join IceCube on this journey of discovery.  >> So this is an event happening at the Milwaukee Public Museum November 21st, and I believe in December, I don't know if it is on the calendar, there will be somebody talking about this here at the Wednesday Nite at the Lab. And this is really a very exciting moment for neutrino astrophysics. 

It happened many years ago for gamma rays astrophysics where finally gamma ray experiments started to see something once technology became good enough to see gamma rays. That was a good moment for them. Now they don't remember that anymore. [LAUGHTER] But we are basically at that stage several years later. So, let's go back to our previous plot. So now I want to give you a glimpse of interdisciplinary science that we can do in IceCube. Some of them are really important. For example, we are detecting these very high energy events, for example, specific to Bert and Ernie. Of course we have another 28. They also have names of Sesame Street people, puppets, Muppets or whatever. 

These are really the two which are strikingly interesting not reproduced in the atmosphere unless we don't really understand particle physics of cosmic interaction in the atmosphere. One big activity in IceCube is to study whether we really understand the byproducts of cosmic ray interaction in the atmosphere. I'm not talking about origin of cosmic rays anymore. We know that cosmic rays one day will know where they come from but just will detect them. They heat the Earth, they produce neutrinos, and that's our background. But we can transport the background into a signal and try to understand what happens. So then we have to go to particle physics conferences in Fermilab, for example, CERN, and Geneva, say to accelerator physicists and say, look, you guys have to be the accelerators which are much powerful so that you can answer our questions Because, in fact, the physics of the cosmic ray interaction in the atmosphere is actually particle physics, but the energies are so much higher than any possible accelerator ever built on Earth. So we actually witnessing some physics that has not been tested in accelerators, and that's a big problem because right now what we do is to extrapolate what accelerator physics are doing and we assume that we know how to extrapolate, but nature is a little bit tricky and it's not obvious we can always do that. So one thing we can do is to measure the neutrinos produced in the atmosphere, atmospheric neutrinos, and measure their energy distribution. This is a remarkable measurement by itself because even though we don't have to go to extremely high energy and say this must be neutrinos from extragalactic sources. 

We just measure neutrinos produced in the atmosphere and measure their spectrum. We have measured the highest energy neutrinos ever detected on Earth. So this would be, this energy spectrum, energy distribution, will be actually in the textbooks in the future. Actually, I think they already are. And the shape, the precise shape of the spectrum, which is not really a straight line but is a little bit curved, contains a lot of particle physics. So the more precise we measure it, the more we can indirectly test what particle physicists tell us. One interesting thing we can do is to measure the other background before the neutrinos are extracted, the background of the muons. As I said before, when cosmic ray interacts in the atmosphere they produce a lot of things. The two penetrating components that actually can enter into the Earth are neutrinos and muons. We can see a lot of them. 

Three thousand every second. It's huge. And then we can actually use them. We measure them as a fraction of the direction, as a fraction of energy, as a fraction of time. So what we do here, I don't know if you can see, but the black line is just a muon, the relative reaction of the mu rate is every day, and you can see it changes over the season. In July it's the minimum, and in January it's the maximum. July at the South Pole is winter, and January at the South Pole is summer. And the color represents the temperature of the atmosphere over the South Pole, over Antarctica. The top represents the very high atmospheric level in the color picture, and the bottom is the surface. So you see that in September/October where it is spring over there, there is a dramatic change, increase in temperature on the outer layer, and then this produces dilation of the atmosphere. 

The density is lower so the cosmic rays have a little bit hard time to interact, and then it's, sorry, actually they do. But because of the cascading process in the atmosphere, we detect more muons than in winter when the atmosphere is thinner so muons are more difficult to produce because the parent particle that produce the neutrino, they disappear before they produce the muons. There is a huge variation, and the gray line is actually the temperature that we take from weather satellite and we interpret them using particle physics. What will be the temperature that is relevant for our muon. And it actually goes not only the -- reaction is the same, but even the -- are actually going exactly as the temperature is. So, okay, that's interesting. So, we can actually, we are trying to use this data to infer some particle physics information that way. It's a little hard, but this is a possibility to do. But it's also possible to do atmospheric physics. To probe the phenomenon that happen in the upper atmosphere in a way that has not been done before. 

There was one case, this graduate student, this German graduate student Henricha, who actually analyzed the AMANDA data before IceCube was even built, and she wanted to detect very bright events, similar to what we have seen. But AMANDA was too small. It was very hard to see these very energetic neutrinos. She was looking for bright events inside the detector, and what she found instead was this amazing rate variation of the background of the muon around September 2002. And she was desperate, and she had no idea what that was. And then she graduated by eliminating this part of the data in her analysis, and then by chance she talked to a meteorologist and said, yeah, there was a stratospheric warming event at the South Pole, which is very rare in Antarctica. It's much more common in the North Pole where there is no land continent down there. The meteorology is different. But at the South Pole, once spring is starting up, the sun is rising and the atmosphere is heating. So the Antarctic loop currents that surround the ozone hole that is actually always on top of Antarctica has been disrupted dramatically. 

And so the ozone hole is split into two different vortex, and it went away from the Antarctic continent. So on top of the Antarctic continent, the temperature of the atmosphere has risen by 40 degrees Kelvin. 40 degrees C, basically. So 80 degrees Fahrenheit. It's a huge variation in temperature. So from a particle physics point of view, the density of the air has changed in a week so much that many more muons have been detected. So that's actually very interesting. One can do a reverse engineering here. Say, okay, let me believe particle physics. I know that how muons are produced, let me actually take the mu variation on a daily base and see what I can do. 

And there are ideas to use the mu variation as a function of a daily temperature to measure the winds, the wind speed in the upper atmosphere. These are very interesting possibilities and perhaps meteorologists know much more physics than me on that. Another interesting thing that can be done that has been done is to use a different part of IceCube that has been built at the surface. I really didn't mention it, but we do also have a cosmic ray detector at the surface just on top of the buried strings. The can tell exactly the same optical sensors, which are put in these big tanks of frozen ice, obviously. So cosmic rays, a soft component of cosmic rays interaction that cannot penetrate in the ice, it actually gets into this tank and then we can detect their presence. So once in the while there are solar flares, especially during the maximum activity of the sun that happened, basically, now. The sun activity is going down again. But the sun has this 11-year period, and then during the maximum there are many sorts of flares. They're this little explosion on the surface of the sun. 

And there is, oh, sorry. And I went one too many. And during this solar flare event, after a few hours we can see that the soft component of the cosmic rays, or the low energy cosmic rays, actually have an increase in rate. And this happens, there is a monitoring around the world, and the South Pole is only one of them. And by cross-calibrating the different time when this happened across the world, a lot of information can be gathered about the flare. So perhaps we are talking about this enhancement of cosmic rays, they have to be associated to acceleration properties. So during this flare magnetic fields actually kick protons that are emitted by the sun, and they give them more energy, and when the heat the Earth, they actually go beyond the normal level. And the understanding of this acceleration process is really fundamental because it can be the root to understand how cosmic rays are accelerated very far away from us. And the sun is a perfect laboratory very close to us. Another event in the sun that is associated somehow to solar flare is the coronal mass ejection. 

It's a much more massive a phenomenon of this massive explosion, and the loop of the coronal mass ejection that you can see here can be, sorry, I never know how to do this, okay, can be so big that many Earths can be put along the loop produced. And what they produce when they are so gigantic, so they propagate in the space between the sun and the Earth, eventually they heat the Earth, and what they do is the opposite of the enhancement. They actually create a depletion of cosmic rays, which is called --. So this can be studied also in very detail. The timing distribution and the duration of the increase and then the slow increase of cosmic rays when the coronal mass ejection has crossed the Earth is actually very important for how your physicist to understand what actually happens as we are in the middle of this coronal mass ejection. And it contains a lot of physics. This is also something that has been done. It's basically been using IceCube as a monitor also for these events. The most important thing for us is the ice. So, basically, IceCube is surrounded by ice. 

The ice we know is transparent, but this is not ice we built in the lab. We didn't build a one-kilometer cube of ice with controlled transparency. This is ice that's been produced in geological times. So we have to know what the optical properties are. We have to know what happens to the photons when they propagate from the events to our sensors so that we have to, from counting the photon we can derive how many have been emitted and from how far away. So this is absolutely important. The ice is the detector, and the optical sensors adjust the detection devices. So a lot of effort over the years, and this is extremely complicated, has been done, has been put to understand the optical properties. There are many different ways of doing that. But, for example, there are two properties we have to measure. 

One is the absorption of photons. Photons propagate in ice, and then they are absorbed by a dust grain or just by the crystal structure of the ice. So it produces a dimming of the photons beam. And then there is scattering. Scattering can also be produced by dust grains or by ice and crystals. Sometimes the crystals are displaced because this is not controlled, the ice is not produced in a controlled way in the lab. So there are discontinuities so the photons can scatter. And the scattering produces not a dimming but a blurring of the image in space and in time. So each optical model has LEDs, these light meters that are calibrated. We know how many photons they emit of a specific color. 

And we just shoot, we just turn on these LEDs for one of the optical models, and we detect the photons from the others. A fraction of the distance we detect, we know how many we emit, we just measure how many we detect and how late they are. So the time distribution is very thin for a nearby optical model from the source and becomes wider in time the farther away you go. So by measuring this in the 3D dimension, you can actually measure the ice properties. And the trick is to disentangle the absorption and scattering because they happen at the same time. This is a complicated analysis, but basically we can derive it's a function of the depth for 1400 meters from the surface of the South Pole to 2500 meters. We can detect how much the light is absorbed and scattered. And you see it's not very simple. It actually goes up and down. And that's because of the geology of the South Pole glacier. 

And by cross-referencing this data with core data done in other parts of the continent, it is possible to identify them with letters, and these are well identified anywhere in the continent, and you can actually identify the age of that layer of the ice when it was produced as a function of the depth. And then each of these correspond to one of the glacial eras in the past. So during the glacial eras, the ice was a much more high, larger in volume and then decreased, and then every time this happens the ice becomes contaminated by dust, more or less, depending on how thick the ice is. Also, Antarctica is extremely active from a volcanic point of view. So there are ages where volcanic ashes have actually been deposited in very thin layers. The way to detect these thin layers, this is a fantastic experiment done by our Berkeley collaborators, they built this instrument called dust logger. This instrument was put in many of the strings during their deployment at the very bottom. During the deployment of the strings where we put the optical models, we put them in the cable, we attach the optical cable to detect their output. This dust logger actually emits light perpendicularly inside the ice, and the more dust or bubbles, the more scattering processes there are, the more light you get back. And the precision of this is on centimeter level. 

So what they did, they actually remeasure the amount of scattering especially, all the layers as a fraction of depth with an incredible precision. And I can show you how. Zoom in at these peaks. Each of them corresponds to a glacial time. At the bottom, you see the depth in meters. At the top, you see the age, the well calibrated age, 50,000 years ago, that corresponds to that layer. And the dust logger is so precise that it can measure time in the past, in geological time, where very thin layers of ashes have been deposited, which produces so much more scattering than the surrounding layers. So this is a very specific climate fingerprint, which is basically the beginning of understanding what actually happens at the South Pole, in this case, from 53,900 to 54,150 years ago. One thousand years of time. It's incredibly detailed. 

So that's a lot of activity in the glaciology environment. Another thing that we do need to know is these dust layers, the dustiest, the more transparent layer, they are not horizontal because of the history of the continent. So, the dust logger, because it has such precise features, you can actually measure this same feature in a different location and see that actually the layers are tilted in a complicated way. So if you go from shallower depths, from 1300 meters down to 2400 meters, you can see the layers of the same optical properties are actually tilted. And we have to use this when we interpret our data. This absolutely important information for us. So the -- is preferentially around this direction, if you can see my... This is basically the fingerprint of the detector looked from above. So this is the one-kilometer across. Each of these dots represents the projection of the string, which is down below. 

And so the tilt is basically along this direction. And by coincidence the ice at the South Pole is still a glacier, it moves 10 meters every year, and it moves in this direction. In fact, generally the first of every year there is the ceremony where the South Pole marker is moved 10 meters apart. And you can see each year an artist built, I should have taken a picture, built a whole piece of art representing the marker. And you can see all the years since the '50s you can see the bottom of the stick 10 meters apart. So it goes very far way. So the ice has moved a lot since the station was built in the early '50s. It's very remarkable. Ten meters. It's a big movement. 

It moves quite a lot. Really impressive. So this movement actually, it might be related to another property of the ice optical properties which is very important in physics. We demonstrated recently it's absolutely important. The optical properties of the light, my mouse is not visible anymore, you see there is this arrow which is called ice flow. This is the direction of the flow of the entire ice shelf on the northwest direction in this coordinate system. And the light propagating in this direction is actually, so the ice, sorry, the light propagating in this direction propagate for much longer distances than light propagating perpendicularly. So somehow the ice properties are not symmetric. If you look in one direction, you see less light from the same sources. If you look in the opposite direction, you see more light. 

There is actually no symmetry. That is important for us from a physics point of view, but then when we talk to glaciologists they start to imagine all the possible scenarios that perhaps the movement of the ice is aligning the dust grains which producing asymmetry in optical properties and the scattering absorption. So this is the first evidence of an isotropy that is very bizarre. This was done by a collaborator here in Madison. Nobody believed him for a very long time until one of these two events, Bert and Ernie, one of the two did look very, very strange, and then once we interpreted the data with this isotropy, it just looked exactly what we expected it to be at that energy. So somehow this is the right property of the ice. Very interesting. Okay, I'm about to finish, and, by chance, we have thermometers in each of our optical models because we have to monitor the temperature of the electronics. If it's too hot, we have to turn them on, off actually, sorry. So we can actually measure the temperature. 

And then of course the optical models are in thermal equilibrium with the ice once the electronic is off. So measurements have been done of the temperature when the detector was off, which doesn't happen very often but it has happened sometimes. So what you measure is the temperature of the ice, and the temperature of the ice is a function of the depth. So zero means the bedrock, that's the bottom of the glacier. And the surface is at 2800 meters. That's where we walk. And the detector is built between 300 meters and 1500 meters. So the temperature actually decreases. Just below the surface is minus 50 degrees C, and at the bottom it's almost zero degrees. And actually, given the pressure of the ice, the melting point is not at zero C, but it's minus two C. 

This number is very important for glaciologists because if we manage to measure the temperature very well, if it is above a freezing temperature, it means that there is a lake, a liquid lake at the bottom of IceCube, and that has a lot of consequences from the glaciology point of view. Tomography, very quickly. So, a very interesting thing that started in the '60s was to put a muon detector by the Egyptian pyramids. So muons, we know where they come from, from the atmosphere, from the impact of cosmic rays, but muons when they cross materials, they lose energy and they scatter in direction. We can measure the dimming of the muons, and we can measure the deviation of the muons. So, in the '60s the idea was I want to see whether there are empty chambers inside the pyramids because emptiness means that the muons are not as absorbed in that specific angle. And the result was there was no empty chamber at that time. They didn't find any emptiness besides the chambers that were already known in the pyramids. So the pyramid is really solid. This technique has been used, Japanese are really, and actually Italians I had discovered, are really ahead of that. 

They are interested in monitoring volcanoes to see what is inside volcanoes. You put a muon detector on the sides and you start the flux of the muons coming from the other side of the mountains and crossing the mountains. You detect the variation of the muon counting as a function of direction. You can detect the magma chamber because it has a different density from the outside rock so it absorbs muons differently. And recently a few years ago after the explosion of the Fukushima reactor, one of the reactors they put only six weeks of a muon detector on one side in two different reactors. One is the damaged one, and one is the undamaged one. They could see that on the top, I don't know if you can see with this light, on the top central portion of the right image is a darker spot which means muons are not as absorbed there as they are below. That's the part of the reactor that has been emptied by the explosion. Nobody can go there because it's highly radioactive. A muon detector has been used only six weeks, they could diagnose, they could actually check how big the void was so they could estimate how much radioactive material has been expelled by the explosion. 

So we start to do neutrinography. Our Japanese collaborator --, she spends 50% of her time in the Earthquake Institute in Tokyo. Japanese are very worried about earthquakes. They really want to know if they can predict them. But the studying of the earthquake goes beyond earthquakes themselves. They want to understand what is inside the Earth, and, strangely enough, we have no clue. Not only we don't know where cosmic rays come from, we have no idea what the Earth is made of, what the density of the Earth is, and whether it's only iron in the core of the Earth or it's lighter material. We only know that the core of the Earth is melted, high temperature, and it produces the magnetic field. That's as much as we know, as far as I understand. So the inner structure of the Earth has been studied with seismic waves. 

Seismic waves can tell, they can propagate through the Earth. Seismic detectors are everywhere so you can actually have a 3D image of a seismic wave after a violent earthquake, and you can actually measure the density gradient of the Earth as deep you go. But of course, and this is fairly well known provided you accept models of the layering of the Earth, it's not a measure where you actually discover things. You have to assume some modeling. And apparently, going to this conference, it seems like there are so many models out there that the seismic waves are important, but you can interpret things in many different ways. So, one thing we can do is this awesome thing called neutrino radiography and this amazing brand new thing called neutrino tomography. So, one is based on the usual idea that neutrinos are absorbed in the Earth. I told you something opposite in the beginning. I told you that neutrinos don't like to interact with the Earth. That's true. 

Neutrinos just cross the Earth as if it doesn't exist, but that's not true at every energy. When neutrinos are high energy enough, they actually do like to interact, and then it's fairly well known how they interact, especially high energy. So they are actually absorbed. The problem is with these high energy neutrinos it will take a long time even for IceCube to detect enough of these very high energy neutrinos from the atmosphere, from the other side of the atmosphere and diagnose or make an image of the interior of the Earth. But the idea is absolutely valid. Neutrino tomography uses a very, a property of the neutrinos which is called oscillation. It's a science by itself. I will just mention what oscillations are in a very, very brief way. It's brand new, and the Japanese geologists are very excited when particle physics go there, or neutrino physics, and say we can do that, and they say, oh, my god, this is fantastic. So, by doing radiography and tomography, you can actually determine maybe in a hundred years from now the chemical composition of the Earth, and this is exactly what geologists need to know. 

So, very briefly, neutrino radiography absorption in the Earth. So basically the detector now is up there. That's the South Pole. I just put it up there. And then it's a function of the distance, sorry, it's a function of the angle where you detect neutrinos. If neutrinos are coming right up, which I call 180 degrees in this case, they have to cross the core, which is much more dense we think, rather than the neutrino coming from the mantle, which is the yellow part of the Earth, which is less dense. So a neutrino coming from the core, just look at the right panel here, they are more absorbed so you should see at high energies, each of these curve at higher and higher energies of the neutrinos. So you can see the slope in the white part of the plot is due to particle physics. They increase probability that neutrinos actually interact in the Earth. And the second part is particle physics given that you have much higher density. 

So if we manage to detect enough neutrino at very high energy here, it will take years, then we can see how this dip is, and we can actually indirectly find what the density of the core is. Tomography, it uses this property which is called oscillations. So I told you before about two types of neutrinos, the muon type of neutrino and the electron type of neutrinos. There is actually another one. It's called tau. And then electron neutrino and tau neutrino in our detector basically behave similarly. They produce events that we call cascade. Events that propagate outward in this kind of pseudospherical way. A mu neutrino will produce an event that's elongated in a track. The problem of the neutrino, which is the other thing that makes them really mysterious, is that they don't have an identity. 

If a neutrino is muon, it changes identity all the time depending on what energy they are. If the energy is right, a mu neutrino can transform itself into an electron neutrino and maybe into a tau neutrino. So it's a very complicated game that had created a huge problem over many, many years. When I was in college, there was a solar neutrino problem. The solar neutrino problem is that the neutrino, low energy neutrinos emitted by the sun were predicted to be three times more than actually were detected. So the idea was there is something wrong in the model of the sun. And actually, a science fiction book was written on that. The sun was actually dying in the book because it emitted much less neutrinos. But in fact the problem was even simpler. Neutrinos transform themselves so the detection was looking for the wrong neutrinos. 

They were still there but we didn't see them. So the mystery of the solar neutrino has been solved. Neutrinos just don't keep their identity. And this is a case, like if you go, this is a neutrino that had given energy for IceCube, a billion electron volt, which as a unit of energy is kind of low. We are detecting neutrinos which are at least a hundred times more energetic than those. But this is the energy were a neutrino changes their nature. What that plot means is that in the horizontal you can see the distance from one kilometer to 12,000 kilometers, which is the diameter of the Earth, and already after a few hundred kilometers, 200 kilometers, mu neutrino has actually already disappeared and became electron neutrino. And then it becomes a muon again and an electron again, and eventually it oscillates so fast that at the end on the other side of the Earth you can see only 50% of them. So somehow there's a missing 50% of mu neutrinos. But that's no mystery because they are not muons anymore. 

If you detect an electron neutrino, then you count 100%. So, what does that have to do with the tomography? Because things are getting really fancy now, neutrinos oscillate in a vacuum with very clear properties but they oscillate in matter with slightly different properties. Because matter is dense, there are a lot of electrons around the atoms. These electrons influence the way neutrino oscillate, and that now is well known and has been tested by accelerator experiments. It's getting more and more known. So, if we manage in the future to have a big IceCube that detects neutrino at such low energy which now is below our threshold, we can measure as a function of energy neutrinos coming just from below, from the North Pole, to the core and up. For example, in this specific case we can measure different energy how a mu neutrino is transformed itself into an electron neutrino and so forth. And in the future where an accelerator experiment will give us much better parameters from the particle physics point of view so that we can model this oscillation much better with smaller errors. We can actually identify the difference between the blue and the red, which is an iron core versus a very light core made of hydrogen, which are completely two different models. And geologists are extremely excited by this possibility; although, they probably don't know that it will take a long time. 

Thank you very much. [APPLAUSE]