Klein and Stezelberger

Spectrum

Physicist Spencer Klein and Electrics Engineer Thorsten Stezelberger, both at Lawrenc Berkeley National Lab, describe the Neutrino Astronomical project IceCube, which was recently completed in Antarctica. They also go on to discuss proposed project Arianna.

Transcripts

Speaker 1: Spectrum's next [inaudible]. Welcome to spectrum [00:00:30] the science and technology show on k a l x Berkeley, a biweekly 30 minute program bringing you interviews featuring bay area scientists and technologists as well as a calendar of local events and news.

Speaker 2: Good afternoon. I'm Brad Swift, the host of today's show, Rick Karnofsky and I interview Spencer Klein and Torsten Stessel Berger about the neutrino astronomy project. Ice Cube. Spencer Klein is a senior scientist and group leader at Lawrence Berkeley National Lab. [00:01:00] He's a member of the ice cube research team and the Ariana planning group. Thorsten Stetso Berger is an electronics engineer at Lawrence Berkeley National Lab. He too is part of the ice cube project and the Ariana team. They join us today to talk about the ice cube project and how it is helping to better define neutrinos. Spencer Klein and Thorsten setser Berger. Welcome to spectrum.

Speaker 3: Thank you. Thank you. Can you talk to us a little bit about neutrinos? [00:01:30] Well, neutrinos are subatomic particles which are notable because they barely interact at all. In fact, most of them can go through the earth without interacting. This makes them an interesting subject for astrophysics because you can use them to probe places like the interior of stars where otherwise nothing else can get out and are most of them neutrinos from those sources. There's a wide range of neutrino energies that are studied. Some of the lowest energy neutrinos are solar neutrinos which [00:02:00] come from the interior of our sun. As you move up to higher energies, they come from different sources. We think a lot of the more energetic ones come from supernovas, which is when stars explode, they will produce an initial burst of neutrinos of moderate energy and then over the next thousand years or so, they will produce higher energy neutrinos as ejected spans, producing a cloud filled with shock fronts and you're particularly interested in those high energy.

Speaker 3: Yes, ice cube is designed to study those neutrinos and also [00:02:30] neutrinos from even more energetic neutrinos where we don't really know where they come from. There are two theories. One is that they come from objects called active Galactic Nuclei. These are galaxies which have a super massive black hole at their center and they're rejecting a jet of particles perpendicular, more along their axis. And this jet is believed to also be a site to accelerate protons and other cosmic rays to very high energies. The other possible source of ultra energy neutrinos [00:03:00] are gamma ray bursts, which are when two black holes collide or a black hole collides with a neutron star. And if the neutrinos don't interact or interact so rarely and weekly with matter, how do we actually detect them? Well, the simple answer is you need a very large detector. Ice Cube is one cubic kilometer in volume and that's big enough that we think we should be able to detect neutrinos from these astrophysical sources.

Speaker 3: The other project we work on, Ariana is even bigger. It's [00:03:30] proposed, but it's proposed to have about a hundred cubic kilometers of volume. And so you have an enormous detector to detect a few events and once you detect them, how can you tell where they came from? Well, with ice cube we can get the incoming direction of the neutrinos to within about a degree. So what we do is we look for neutrinos. Most of what we see out of these background atmospheric neutrinos which are produced when cosmic rays interact in the earth's atmosphere. But on top [00:04:00] of that we look for a cluster of neutrinos coming from a specific direction. That would be a clear sign of a neutrino source, which would be, you know, and then we can look in that direction and see what interesting sources lie. That way we can also look for extremely energetic neutrinos which are unlikely to be these atmospheric neutrinos.

Speaker 3: And how is it that you measure that energy? What happens is a neutrino will come in and occasionally interact in the Antarctic. Ice should mention that ice cube is located at the South Pole where [00:04:30] there's 28 hundreds of meters of ice on top of the rock below. Occasionally in Neutrino will come in and interact in the ice and if it's something called a type of neutrino called the [inaudible] Neutrino, most of its energy will go into a subatomic particle called the Meuron. Meuron is interesting because it's electrically charged. As it goes through the ice, it will give off light, something we call Toronto radiation. So we've instrumented this cubic kilometer of ice with over 5,000 optical [00:05:00] modules, which are basically optical sensors. And so we record the amount and arrival times of the light at these optical sensors. And from that we can determine the neutrino direction to about within a degree.

Speaker 3: And we can also get an estimate of the energy. Um, essentially is the on is more energetic. It will also produce other electrically charged particles as it travels. Those will give off more light. And so the light output is proportional to the neutrino energy. So you're taking an advantage of the fact that there's [00:05:30] a lot of ice in Antarctica and also that it's very big. Are there other reasons to do it at the South Pole? Well, the other critical component about the ice is that it has to be very clear, shouldn't scatter light and it shouldn't absorb light. And in fact the light can travel up to 200 meters through the ice before being absorbed. This is important because that means we can have a relatively sparse array. You know, we have only 5,000 sensors spread over a cubic kilometer. That's only if the light can travel long distances through the ice. [00:06:00] And do you have to take into account that the ice in the Antarctic is not perfectly clean? Yes. When we reconstruct the neutrino directions, we use this sophisticated maximum likelihood fitter. Essentially we try all sorts of different Milan directions and see which one is the most likely. And that takes into account the optical properties of the ace and includes how they vary with depth. There are some dust layers in the ice where the absorption length is much shorter and some places, [00:06:30] well most of the ice where it's much better.

Speaker 4: Our guests on spectrum today are Spencer Klein and Thorsten Stetson Burger from Lawrence Berkeley national lab. They are part of a physics project named Ice Cube. In the next segment they talk about working at the South Pole. This is KALX Berkeley.

Speaker 3: Can you compare the two experiments, both ice Cuban on a little bit? Well, ice cube is designed [00:07:00] for sort of moderate energy neutrinos, but for the really energetic neutrinos are, they are rare enough so that a one cubic kilometer detector just isn't big enough. And so for that you need something bigger and it's hard to imagine how you could scale the optical techniques that ice cube uses to larger detectors. So that's why we looked for a new technique in it. Here I should say we, the royal, we either many people, many places in the world looking at different versions. And so what we've chosen is looking [00:07:30] for radio [inaudible] off the mission. You know, we have this interaction in the ice. Some of the time. If it's an electron Neutrino, it produces a compact shower of particles. That shower will have more negatively charged particles than positively charged.

Speaker 3: And so it will emit radio waves, you know, at frequencies up to about a Gigahertz coherently, which means that the radio emission strength depends on the square of the neutrino energies. So when you go to very high neutrino energies, this is a preferred technique. Radio waves can [00:08:00] travel between 300 meters and a kilometer in the ice, which means you can get by with a much sparser array. So you can instrument a hundred cubic kilometers with a reasonable number of detectors. When Ariane is developed, it will get to access higher energies. Will it still didn't detect some of the moderately high energies that ice cube is currently reaching? No, and there's no overlap because of the coherence and just not sensitive. I mean, ice cube will occasionally see these much higher energy neutrinos, [00:08:30] but it's just not big enough to see very many of them. Uh, you commented on, or you mentioned the size of the collaboration.

Speaker 3: Can you sort of speak about how big these projects are? Sure. Ice Cube has got about 250 scientists in it from the u s Europe, Barbados, Japan, and New Zealand. Oh yeah. And plus one person from Australia now. And that's a well established, you know, it's a large experiment. Arianna is just getting going. It's got, I'll say less than a dozen [00:09:00] people in it. Mostly from UC Irvine and some involvement from LDL. How many years have you had experience with your sensors in the field then? That's kind of a complicated question and that the idea of doing neutrino astronomy in the Antarctic ice has been around for more than 20 years. The first efforts to actually put sensors in the ice, we're in the early 1990s these used very simple sensors. We just had a photo multiplier tube, essentially a very sensitive [00:09:30] optical detector, and they sent their signals to the surface. There are no complicated electronics in the ice.

Speaker 3: The first Amanda effort in fact failed because the sensors were near the surface where the light was scattering very rapidly. Turns out the upper kilometer of ice is filled with little air bubbles, but then as you get down in depth, there's enough pressure to squeeze these bubbles out of existence. And so you go from very cloudy ice like what you see if you look in the center of an ice cube and then you go deeper [00:10:00] and you end up with this incredibly clear ice. So the first efforts were in this cloudy ice. Then in the second half of the 1990s Amanda was deployed in the deep highs. This is much smaller than ice cube in many respects. The predecessor, of course, the problem with Amanda was this transmission to the surface. It worked but it was very, very touchy and it wasn't something you could scale to the ice cube size. So one where people got together and came up with these digital optical modules where all of the digitizing electronics [00:10:30] is actually in the module. We also made a lot of other changes and improvements to come up with a detector that would be really robust and then we deployed the first ice cube string in 2005 and continued and then the last string was deployed at the end of 2010

Speaker 5: so basically from the scientific point or engineering point of view, we're learning about the detector. We got data from the first strain. It was not very useful for take neutrino science but you can learn to understand [00:11:00] the detector, learn how the electronics behaves, if there is a problem, change code to get different data.

Speaker 3: When we did see some new is in that run and there's this one beautiful event where we saw this [inaudible] from a neutrino just moving straight up the string. I think it hit 51 out of the 60 optical sensors. So we're basically tracking it for 800 meters. It was just a beautiful that

Speaker 5: what is the lifelight down there? The food, the day to day, [00:11:30] we've never been there in the winter time, so I can only talk about a summer and in the summer you're there for something specific like drilling or deploying a, so to summertime keeps you pretty busy and you do your stuff and then afterwards you hang out a little bit to wind down. And sometimes with some folks playing pool or ping pong or watching movies or just reading something and then time [00:12:00] again for the sleep or sleeping. And the next day for drawing for example, we had three shifts. And so that kept you pretty, pretty busy. One season when I was thrilling there I was on what we call the graveyard shift. Starting from 11 to I think eight in the morning. I saw and yeah, it was daylight. You don't notice it except you always get dinner for breakfast and scrambled eggs and potatoes for dinner.

Speaker 3: The new station at the South Pole is really very nice and I would [00:12:30] say quite comfortable, good recreational facilities. I mean, and I would say the food was excellent, really quite impressive and you get to hang out with a bunch of international scientists that are down there. How collegial isn't, it

Speaker 5: depends a little bit on the work. Like when I was rolling on night shift, we mostly got to hang out with people running the station. That was fairly collegial.

Speaker 3: There's actually not very many scientists at the South Pole. In the summer there were about 250 [00:13:00] people there and maybe 20 of them were scientists. Most of them were people dealing with logistics. These are people, you know, heavy equipment operators. Fuel Lees would get the fuel off of the plane, cooks people, and even then can building the station wasn't quite done yet. The drillers will lodge wide variety of occupations but not all that many scientists. How close are the experiments to the station?

Speaker 5: They are quite a few experiments [00:13:30] based in the station. Ice Cube is a kilometer away about probably

Speaker 3: Lamotta and a half to the, to the ice cube lab, which is where the surface electronics is located.

Speaker 5: So it's pretty close walking distance called walk. But it depends. I mean I don't mind the calls or it was a nice walk but they have like ice cube, uh, drilling. We are like lunch break also. It's [00:14:00] a little bit far to walk kilometer out or even throughout depending where you drill. So we had a car to drive back and forth to the station to eat lunch. Otherwise you are out for too long.

Speaker 3: Yeah, they give you a really good equipment and so it's amazing how plaza you can be about walking around when it's 40 below, outside.

Speaker 5: Especially if you do physical work outside as part of drilling also. It's amazing how much of that cold weather Ikea you actually take off because you just [00:14:30] do staff and you warm up.

Speaker 4: [inaudible] you are listening to spectrum on KALX Berkeley coming up, our guests, Spencer Klein and Torsten Stotzel Burger detail, the ice cube data analysis process,

Speaker 3: the ongoing maintenance of Ice Cube Sarah Plan for its lifetime

Speaker 5: for the stuff [00:15:00] in the eyes, it's really hard to replace that. You cannot easily drill down and take them out. They are plans, uh, to keep the surface electronics, especially the computers update them as lower power hardware becomes available. Otherwise I'm not aware of preventive maintenance. You could do with like on a car. Yeah.

Speaker 3: I have to say the engineers did a great job on ice cube. About 98% of the optical modules are working. Most of the failures were infant [00:15:30] mortality. They did not survive the deployment when we've only had a handful of optical modules fail after deployment and all the evidence is we'll be able to keep running it as long as it's interesting. And is there a point in which it's no longer interesting in terms of how many sensors are still active? I think we'll reach the point where the data is less interesting before we run out of sensors now. Okay. You know, we might be losing one or two sensors a year. In fact, we're still at the point where [00:16:00] due to various software improvements, including in the firmware and the optical modules, each year's run has more sensors than the previous years. Even if we only had 90% of them working, that would be plenty.

Speaker 3: And you know, that's probably a hundred years from now. What do we have guests on to speak about the LHC at certain they were talking about the gigantic amounts of data that they generate and how surprisingly long it takes for scientists to analyze that data to actually get a hold [00:16:30] of data from the detector. And you're generating very large amounts of data. And furthermore, it's in Antarctica. So how much turnaround time is there? Well, the Antarctica doesn't add very much time. We typically get data in the north within a few days or a week after it's taken. There is a bit of a lag and try and take this time to understand how to analyze the data. For example, now we're working on, for the most part, the data that was taken in 2010 and [00:17:00] you know, hope to have that out soon probably for summer conferences. But understanding how to best analyze the data is not trivial. For example, this measurement of the mule on energies, very dependent on a lot of assumptions about the ice and so we have ways to do it now, but we're far from the optimal method

Speaker 5: and keep in mind that detector built, it's just finished. So before you always added in a little bit more. So each year the data looked different because you've got more sensors in the data.

Speaker 3: [00:17:30] Let's say for things where turnaround is important. For example, dimension, these gamma ray bursts, there's where this happens when a bunch of satellites see a burst of x-rays or gamma rays coming from somewhere in the sky. They can tell us when it happened and give us an estimate of the direction. We can have an and I would say not quite real time, but you know that we could have turned around if a couple of weeks. We also measure the rates in each of the detectors. This is the way to look for low energy neutrinos from a [00:18:00] supernova that is essentially done in real time. If the detector sees an increase, then somebody will get an email alert essentially immediately. If we got one that looked like a Supernova, we could turn that around very quickly. So are the algorithms that you're using for this longer term analysis improving?

Speaker 3: Yes. They're much more sophisticated than they were two years ago. I'd say we're gradually approaching and I'm ask some Todrick set of algorithm, but we're still quite a ways [00:18:30] to go. We're still learning a lot of things. You know, this is very different from any other experiment that's been done. Normally experiments if the LHC, if they are tracking a charged particle, they measure points along the track. In our case, the light is admitted at the trend off angle. About 41 degrees. So the data points we see are anywhere from a few meters to a hundred meters from the track. And because of the scattering of light, it's a not so obvious how to find [00:19:00] the optimum track and it's, you know, it's very dependent on a lot of assumptions and we're still working on that. And we have methods that work well. As I said, you know, we can get an angular resolution of better than a degree in some cases, but there's still probably some room to be gotten there.

Speaker 5: And then also, I mean I'm not involved in the science, but I hear people have new ideas how to look at a data. So that's still evolving too.

Speaker 3: Yeah. Like you know, one analysis that people are working on, but we don't have yet would [00:19:30] be a speculative search where you're looking for a pair of event, a pair of neo-cons going upward through the detector in the same direction at the same time, which would quite possibly be a signal of some sort of new physics. And it's certainly an interesting typology to look for, but we're not there yet. And are there different teams looking at the same data to try to find different results and broaden the search so to speak? Uh, yes. We have seven or eight different physics working [00:20:00] groups in each of those groups is concentrating on a different type of physics or a different class of physics. For example, one group is looking for point sources, you know, hotspots in the sky. Second Group is looking at atmospheric and diffuse neutrinos trying to measure the energy spectrum of the neutrinos.

Speaker 3: We do see both the atmospheric and also looking for an additional component. There's a group doing cosmic ray physics. There's a group looking for exotic physics. These are things like these pairs [00:20:30] of upward going particles. Also looking for other oddities such as magnetic monopoles. There's a group that's looking for neutrinos that might be produced from weakly interacting. Massive particles, IAA, dark matter, but there's a group that's monitoring the rates of the detector. This scalers looking for Supernova and oh, there's also a group looking for talented Trinos, which is the this very distinctive topology town. Neutrinos are sort of the third flavor of neutrinos and those are [00:21:00] mostly only produced by extraterrestrial sources and they look very distinctively. You would look for case where you see two clusters of energy and the detector separated by a few hundred meters.

Speaker 5: Looking at what's next, what would be the sort of ideal laboratory? If you want something that's very big, obviously Antarctica is a great challenge. Can you do neutrino detection in space for instance? [inaudible]

Speaker 3: hmm, that's an interesting question. There are people who [00:21:30] are talking about that and the main application is trying to look for these cosmic gray air showers. The best experiments to study high energy, cosmic gray air showers are these things called air shower arrays, which are an array of detectors. Um, the largest one is something called the OJ Observatory in Argentina. It covers about 3000 square kilometers with an array of detectors on kind of a one and a half kilometer grid. And that's about as largest surface detector as you could imagine. Building the alternative [00:22:00] technology is look for something called air fluorescents. When the showers go through the air, they light it up. Particularly the nitrogen is excited and in that kind of like a fluorescent tube. So you see this burst of light as the shower travels through the atmosphere. O J in addition to the surface detectors has these cameras called flies eyes that look for this fluorescence, but it's limited in scale. And people have proposed building experiments that would sit on satellites or a space station [00:22:30] and look down and look at these showers from above. They could cover a much larger area. They could also look for showers from upward going particles, I. E. Neutrino interactions. But at this point that's all pretty speculative.

Speaker 5: And when's your next trip to Antarctica? Uh, that's all depending on funding. I would like to go again and hopefully soon. I think I'm cautiously optimistic. We'll be able to go again this year. Hmm. Spencer in Thorsten. Thanks for joining us. Thank you. Thank you.

Speaker 4: [00:23:00] [inaudible] regular feature of spectrum is to mention a few of the science and technology events that are happening locally over the next few weeks. Lisa Katovich joins me for that

Speaker 6: calendar. The August general meeting of the East Bay Astronomical Society is Saturday, July 14th at the Chabot space and science centers, Dellums [00:23:30] building 10,000 Skyline Boulevard in Oakland. Ezra Bahrani is the evening Speaker. The title of his talk is UFOs, the proof, the physics and why they're here. The meeting starts at 7:30 PM

Speaker 2: join Nobel laureates and social and environmental justice advocates at the towns and Tay Gore third annual seminar for Science and technology on behalf of the peoples of Bengali and the Himalayan basins, the subject, the global water crisis [00:24:00] prevention and solution. Saturday, July 21st 1:30 PM to 7:30 PM the event is jointly sponsored by UC Berkeley's department of Public Health and the international institute of the Bengali and Himalayan basins. Guest Speakers include three Nobel laureates, Charles h towns, Burton Richter and Douglas Ashur off. Also presenting our Francis towns advocate for social justice, Dr. Rush, Gosh [00:24:30] and Sterling Brunel. The event will be held in one 45 Dwinelle hall on the UC Berkeley campus. That's Saturday, July 21st 1:30 PM to 7:30 PM for more details, contact the UC Berkeley School of Public Health,

Speaker 6: the next science at cal lectures on July 21st the talk will be given by Dr Jeffrey Silverman and it's entitled exploding stars, Dark Energy, and the runaway universe. Dr Silverman has been a guest [00:25:00] on spectrum. His research has been in the study of Super Novi. His lecture will focus on how the study of supernovae led to the recent discovery that the universe is expanding, likely due to a repulsive and mysterious dark energy. It was these observations that were recently awarded the 2011 Nobel Prize in physics. The lecture is July 21st at 11:00 AM and the genetics and plant biology building room 100

Speaker 2: next to news stories.

Speaker 6: 3000 species [00:25:30] of mosquitoes are responsible for malaria, dengue, a fever, yellow fever, West Nile virus, and cephalitis and many more diseases. In Burkina Faso alone, residents can expect 200 bytes a day. Rapid resistance to pesticides on the part of malaria mosquitoes has prompted researchers all over the globe to deploy novel strategies against this and other diseases. Targeting Dengue. A fever has an advantage over malaria as only one species. Eighties [00:26:00] Egypt die is responsible for spreading it versus the 20 species responsible for spreading malaria. A British biotechnology company called Oxitec has developed a method to modify the genetic structure of the male eighties Aegypti mosquito transforming it into a mutant capable of destroying its own species. In 2010 they announced impressive preliminary results of the first known test of 3 million free flying transgenic mosquitoes engineered [00:26:30] to start a population crash after infiltrating wild disease spreading eighties a Gyp dye swarms on Cayman Island.

Speaker 6: Oxitec has recently applied to the FDA for approval of its mosquito in the u s with Key West under consideration as a future test site in 2009 key west suffered its first dengate outbreak in 73 years. Australian researchers are testing and mosquito intended to fight dengue, a fever bypassing the disruptive Wolbachia bacteria to other mosquitoes, a very [00:27:00] different approach than transgenic genes funded largely by the bill and Melinda Gates Foundation. The project has shown that the Wolbachia strain not only shortens the life of a mosquito, but also reduces the amount of virus it develops. Releases in Queensland, Australia last year showed that Wolbachia could spread through a wild population quickly and future test sites are under consideration. In Vietnam.

Speaker 2: The UC Berkeley News Center reports a prototype network being installed by chemists at the University of California. Berkeley [00:27:30] will employ 40 sensors spread over a 27 square mile grid. The information the network will provide could be used to monitor local carbon dioxide emissions to check on the effectiveness of carbon reduction strategies now mandated by the state, but hard to verify built and installed by project leader Professor Ron Cohen and graduate student Virginia Tighe and their lab colleagues. The shoe box size sensors will continuously measure carbon dioxide, carbon monoxide, [00:28:00] nitrogen dioxide, and ozone levels as well as temperature, pressure and humidity streaming. The information live to the web through the site. beacon.berkeley.edu the sensor network dubbed Beacon stretches from the East Bay regional parks on the east to interstate eight 80 on the west from El Surrito on the north nearly to San Leandro on the south encompassing open space as well as heavily traffic areas. [00:28:30] Most of the sensors are being mounted on the roofs of local schools in order to get students interested in the connection between carbon dioxide emissions and climate change. The UC Berkeley researchers work with Oakland's Chabot space and science center to create middle school and high school activities using live sensor data stream through the web as part of the students energy and climate science curriculum. The beacon network is a pilot program funded by the National Science Foundation to determine what information can be learned [00:29:00] from a densely spaced network

Speaker 1: [inaudible].

Speaker 2: The music heard during the show is from most done at David's album, folk and acoustics made available through a creative Commons license 3.0 attribution.

Speaker 1: Thank you for listening to spectrum. If you have comments about the show, please send them to us via email. Our email address [00:29:30] is spectrum dot [e-mail] join us in two weeks at this same time. [inaudible].

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