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Posts Tagged ‘IceCube’

The World’s Largest Detector?

Wednesday, August 13th, 2014

This morning, the @CERN_JOBS twitter feed tells us that the ATLAS experiment is the world’s largest detector:

CERN_JOBS Tweet Largest Detector

Weighing over 7,000 tons, 46 meters long, and 25 meters high, ATLAS is without a doubt the particle detector with the greatest volume ever built at a collider. I should point out, though, that my experiment, the Compact Muon Solenoid, is almost twice as heavy at over 12,000 tons:


CMS is smaller but heavier — which may be why we call it “compact.” What’s the difference? Well, it’s tough to tell from the pictures, in which CMS is open for tours and ATLAS is under construction, but the big difference is in the muon systems. CMS has short gaps between muon-detecting chambers, while ATLAS has a lot of space in order to allow muons to travel further and get a better measurement. That means that a lot of the volume of ATLAS is actually empty air! ATLAS folks often say that if you could somehow make it watertight, it would float; as a CMS member, I heartily recommend attempting to do this and seeing if it works. 😉

But the truth is that all this cross-LHC rivalry is small potatoes compared to another sort of detector: the ones that search for neutrinos require absolutely enormous volumes of material to get those ghostlike particles to interact even occasionally! For example, here’s IceCube:

"Icecube-architecture-diagram2009" by Nasa-verve - IceCube Science Team - Francis Halzen, Department of Physics, University of Wisconsin. Licensed under Creative Commons Attribution 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Icecube-architecture-diagram2009.PNG#mediaviewer/File:Icecube-architecture-diagram2009.PNG

Most of its detecting volume is actually antarctic ice! Does that count? If it does, there may be a far bigger detector still. To follow that story, check out this 2012 post by Michael Duvernois: The Largest Neutrino Detector.


There’s a software tool I use almost every day, for almost any work situation. It’s good for designing event selections, for brainstorming about systematic errors, and for mesmerizing kids at outreach events. It’s good anytime you want to build intuition about the detector. It’s our event viewer. In this post, I explain a bit about how I use our event viewer, and also share the perspective of code architect Steve Jackson, who put the code together.

Steamshovel event viewer showing the event Mr. Snuffleupagus

The IceCube detector is buried in the glacier under the South Pole. The signals can only be read out electronically; there’s no way to reach the detector modules after the ice freezes around them. In designing the detector, we carefully considered what readout we would need to describe what happens in the ice, and now we’re at the stage of interpreting that data. A signal from one detector module might tell us the time, amplitude, and duration of light arriving at that detector, and we put those together into a picture of the detector. From five thousand points of light (or darkness), we have to answer: where did this particle come from? Does the random detector noise act the way we think it acts? Is the disruption from dust in the ice the same in all directions? All these questions are answerable, but the answers take some teasing out.

To help build our intuition, we use event viewer software to make animated views of interesting events. It’s one of our most useful tools as physicist-programmers. Like all bits of our software, it’s written within the collaboration, based on lots of open-source software, and unique to our experiment. It’s called “steamshovel,” a joke on the idea that you use it to dig through ice (actually, dig through IceCube data – but that’s the joke).

Meet Steve Jackson and Steamshovel

IceCube data from the event Mr. Snuffleupagus

Steve Jackson’s job on IceCube was originally maintaining the central software, a very broad job description. His background is in software including visualizations, and he’s worked as The Software Guy in several different physics contexts, including medical, nuclear, and astrophysics. After becoming acquainted with IceCube software needs, he narrowed his focus to building an upgraded version of the event viewer from scratch.

The idea of the new viewer, Steamshovel, was to write a general core in the programming language C++, and then higher-level functionality in Python. This splits up the problem of drawing physics in the detector into two smaller problems: how to translate physics into easily describable shapes, like spheres and lines, and how to draw those spheres and lines in the most useful way. Separating these two levels makes the code easier to maintain, easier to update the core, and easier for other people to add new physics ideas, but it doesn’t make it easier to write in the first place. (I’ll add: that’s why we hire a professional!) Steve says the process took about as long as he could have expected, considering Hofstadter’s Law, and he’s happy with the final product.

A Layer of Indirection 

As Steve told me, “Every problem in computer science can be addressed by adding a layer of indirection: some sort of intermediate layer where you abstract the relevant concepts into a higher level.” The extra level here is the set of lines and spheres that get passed from the Python code to the C++ code. By separating the defining from the drawing, this intermediate level makes it simpler to define new kinds of objects to draw.

A solid backbone, written with OpenGL in C++, empowers the average grad student to write software visualization “artists” as python classes. These artists can connect novel physics ideas, written in Python, to the C++ backbone, without the grad student having to get into the details of OpenGL, or, hopefully, any C++.

Here’s a test of that simplicity: as part of our week-long, whirlwind introduction to IceCube software, we taught new students how to write a new Steamshovel artist. With just a week of software training, they were able to produce them, a testament to the usability of the Steamshovel backbone.

This separation also lets the backbone include important design details that might not occur to the average grad student, but make the final product more elegant. One such detail is that the user can specify zoom levels much more easily, so graphics are not limited to the size of your computer screen. Making high-resolution graphics suitable for publication is possible and easy. Using these new views, we’ve made magazine covers, t-shirts, even temporary tatoos.

Many Platforms, Many People

IceCube has an interesting situation that we support (and have users) running our software on many different UNIX operating systems: Mac, Ubuntu, Red Hat, Fedora, Scientific Linux, even FreeBSD. But we don’t test our software on Windows, which is the standard for many complex visualization packages: yet another good reason to use the simpler OpenGL. “For cross-platform 3D graphics,” Steve says, “OpenGL is the low-level drawing API.”

As visualization software goes, the IceCube case is relatively simple. You can describe all the interesting things with lines and spheres, like dots for detector modules, lines and cylinders for the cables connecting them or for particle tracks, and spheres of configurable color and size for hits within the detector. There’s relatively little motion beyond appearing, disappearing, and changing sizes. The light source never moves. I would add that this is nothing – nothing! – like Pixar. These simplifications mean that the more complex software packages that Steve had the option to use were unnecessarily complex, full of options that he would never use, and the simple, open-source openGL was perfectly sufficient.

The process of writing Steamshovel wasn’t just one-man job (even though I only talked to one person for this post). Steve solicited, and received, ideas for features from all over the collaboration. I personally remember that when he started working here, he took the diligent and kind step of sitting and talking to several of us while we used the old event viewer, just to see what the workflow was like, the good parts and the bad. One particularly collaborative sub-project started when one IceCube grad student, Jakob, had the clever idea of displaying Monte Carlo true Cherenkov cones. We know where the simulated light emissions are, and how the light travels through the ice – could we display the light cone arriving at the detector modules and see whether a particular hit occurred at the same time? Putting together the code to make this happen involved several people (mainly Jakob and Steve), and wouldn’t have been possible coding in isolation.

Visual Cortex Processing

The moment that best captured the purpose of a good event viewer, Steve says, was when he animated an event for the first time. Specifically, he made the observed phototube pulses disappear as the charge died away, letting him see what happens on a phototube after the first signal. Animating the signal pulses made the afterpulsing “blindingly obvious.”

We know, on an intellectual level, that phototubes display afterpulsing, and it’s especially strong and likely after a strong signal pulse. But there’s a difference between knowing, intellectually, that a certain fraction of pulses will produce afterpulses and seeing those afterpulses displayed. We process information very differently if we can see it directly than if we have to construct a model in our heads based on interpreting numbers, or even graphs. An animation connects more deeply to our intuition and natural instinctive processes.

As Steve put it: “It brings to sharp relief something you only knew about in sort of a complex, long thought out way. The cool thing about visualization is that you can get things onto a screen that your brain will notice pre-cognitively; you don’t even have to consciously think to distinguish between a red square and a blue square. So even if you know that two things are different, from having looked carefully through the math, if you see those things in a picture, the difference jumps out without you even having to think about it. Your visual cortex does the work for you. […] That was one of the coolest moments for me, when these people who understood the physics in a deep way nonetheless were able to get new insights on it just by seeing the data displayed in a new way. ”

And that’s why need event viewers.


Today at the Neutrino2014 conference in Boston, the IceCube collaboration showed an analysis looking for standard atmospheric neutrino oscillations in the 20-30 GeV region. Although IceCube has seen oscillations before, and reported them in a poster at the last Neutrino conference, in 2012, this plenary talk showed the first analysis where the IceCube error bands are becoming competitive with other oscillation experiments.

IC86Multi_NuMuOsc_results_Pscan_V1Neutrino oscillation is a phenomenon where neutrinos change from one flavor to another as they travel; it’s a purely quantum phenomenon. It has been observed in several contexts, including particle accelerators, nuclear reactors, cosmic rays hitting the atmosphere, and neutrinos traveling from our Sun. This is the first widely accepted phenomenon in particle physics that requires an extension to the Standard Model, the capstone of which was the observation of the Higgs boson at CERN. Neutrinos and neutrino oscillations represent the next stage of particle physics, beyond the Higgs.

IC86Multi_NuMuOsc_results_LEOf the parameters used to describe neutrino oscillations, most have been previously measured. The mixing angles that describe oscillations are the most recent focus of measurement. Just two years ago, the last of the neutrino mixing angles was measured by the Daya Bay experiment. Of the remaining mixing angles, the atmospheric angle accessible to IceCube remains the least constrained by experimental measurements.  

IceCube, because of its size, is in a unique position to measure the atmospheric mixing angle. Considering neutrinos that traverse the diameter of the Earth, the oscillation effect is the strongest in the energy region from 20 to 30 GeV, and an experiment that can contain a 20 GeV neutrino interaction must be very large. The Super Kamiokande experiment in Japan, for example, also measures atmospheric oscillations, but because of its small size relative to IceCube, Super Kamiokande can’t resolve energies above a few GeV. At any higher energies, the detector is simply saturated. Other experiments can measure the same mixing angle using accelerator beamlines, like the MINOS experiment that sends neutrinos from Fermilab to Minnesota. Corroborating these observations from several experimental methods and separate experiments proves the strength of the oscillation framework.

The sheer size of IceCube means that neutrinos have many chances to interact and be observed within the detector, giving IceCube a statistical advantage over other oscillation experiments. Even after selecting only the best reconstructed events, the experimental sample remaining still has over five thousand events from three years of data. Previous atmospheric oscillation experiments base analysis on hundreds or fewer events, counting instead on precise understanding of systematic effects. 

The IceCube collaboration is composed of more than 250 scientists from about 40 institutions around the world, mostly from the United States and Europe. The current results are possible because of decades of planning and construction, dedicated detector operations, and precise calibrations from all over the IceCube collaboration.

IceCube has several major talks at the Neutrino conference this year, the first time that the collaboration has had such a prominent presence. In addition to the new oscillations result, Gary Hill spoke in the opening session about the high energy astrophysical neutrinos observed over the last few years. Darren Grant spoke about the proposed PINGU infill array, which was officially encouraged in the recent P5 report. IceCube contributed nine posters on far-ranging topics from calibration and reconstruction methods to a neutrino-GRB correlation search. The conference-inspired display at the MIT museum is about half IceCube material, including an 8-foot tall LED model of the detector. One of three public museum talks on Saturday will be from (yours truly) Laura Gladstone about the basics of IceCube science and life at the South Pole.

One new aspect of the new oscillation analysis is that it uses an energy reconstruction designed for the low end of the energy range available to IceCube, in the tens-of-GeV range. In this range, only a handful of hits are visible for each event, and reconstructing directional information can be tricky. “We took a simple but very clever idea from the ANTARES Collaboration, and rehashed it to tackle one of our biggest uncertainties: the optical properties of the ice. It turned out to work surprisingly well,” says IceCuber Juan Pablo Yanez Garza, who brought the new reconstruction to IceCube, and presented the result in Boston.  By considering only the detector hits that arrive without scattering, the reconstruction algorithm is more robust against systematic errors in the understanding of the glacial ice in which IceCube is built. 


The IceCube Moon Shadow

Monday, June 2nd, 2014

In a previous post, Marcos Santander wrote about a paper he and other IceCubers were working on looking for the shadow of the Moon in  cosmic rays raining down on Earth. Now that paper has been published!

The shadow of the Moon as was observed with the 59-string configuration of IceCube.

The idea of the Moon shadow is simple: to make sure that our detector is pointed the way we think it’s pointed, we look for a known source. The Moon makes a very nice known source, because it blocks cosmic rays from reaching the Earth, and so we see a deficit of cosmic ray air showers (and thus the muons they produce) from the direction of the Moon. By seeing the deficit where we expect it, we know that we can trust directions within the detector, or as the paper puts it, “this measurement validates the directional reconstruction capabilities of IceCube.”

It’s always funny adding the language of modern statistical significance to discussions like this, because they make it sound rather absurd (at least using the frequentist school of statistics). We talk about the random probability that a null (boring) hypothesis could produce the same signal, so smaller probabilities are more significant, and we talk about those probabilities in terms of the area under a “normal” or “gaussian” distribution, measured in the width sigma of that gaussian. A 2-sigma result is farther out in the tail of the gaussian, and less likely (so more significant) than a 1-sigma result.

We’ve arrived at a convention in particle physics that when your data reach 3-sigma significance, you can call it “evidence,” and when they reach 5 sigma, you can call it “discovery.” That’s purely convention, and it’s useful, although scientists should know the limits of the terminology.

That leads to absurd sounding lines like “IC22 has seen evidence of the Moon, while IC40 and IC59 have discovered it.” This is, technically, correct. What we’re really discovering here, though, is not that the Moon exists but that the IceCube detector works the way we expect it to.

Another consideration demonstrated by this paper is that it takes a long time to get a paper through the publication process. Now that the whole process is completed, we can celebrate. I’ve been following this analysis since I started working on it for my masters thesis, then handed it off to other IceCubers while I switched to neutrino oscillations. Do any of you have stories of long review processes?  Does anyone have a favorite other experiment that has looked at the Moon shadow?


Since IceCube was proposed, people have been claiming that you can get a new view of astrophysics by using particles instead of light, and we were pretty sure what the journey would look like. It hasn’t gone quite in the order we expected, but we’re getting that new view of astrophysics, and also, a few years later, filling in the steps we expected to fill first. When we find bits of scientific evidence in a different order than we expected, does that change how excited we get about them?

Sunrise over the IceCube laboritory

The sunrise at the South Pole over the IceCube laboratory, the central building on top of the IceCube Neutrino Observatory.

We been expanding astronomy since it started. First, astronomers used telescopes to resolve visible light better. Later, they expanded to different regions of the light spectrum like x-rays and gamma rays.  Then, it was a small step to expand from gamma rays, which are easier to think of as particles than as waves, to particles like the atomic nuclei that make up cosmic rays. Neutrinos are another kind of particle we can use for astronomy, and they have unique advantages and challenges.

The hard part about using neutrinos as a messenger between the stars and us is that neutrinos very rarely interact with matter. This means that if thousands pass through our detector, we might only see a few. There are some ways around this, and the biggest trick IceCube uses is to look in a very large volume. If we look for more neutrinos at a time, we have more of a chance of seeing the few that interact. The other trick is that we concentrate on high energies, where the neutrinos have a higher chance of interacting in our detector.

The great thing about using neutrinos as a messenger is that they hardly ever interact, so almost nothing can stop them from arriving at our door. If we see a neutrino in IceCube, it came to us directly from something interesting. We know that its direction wasn’t deflected in any magnetic fields, and it wasn’t dimmed by dust clouds or even asteroid clouds. Every (rare) time we see a high-energy neutrino, it tells us something about the stars, explosions, or black holes that created it.

That’s the story that people like Francis Halzen used to get funding for IceCube originally, and around Madison we still get to hear him tell this story, with his inimitable accent, when he speaks at museums or banquets.

Comparing neutrino astronomy to other new 20th century advances in astronomy, we expected the development of the field to follow a certain story.

We expected that first we would see a “diffuse” signal. This would be part of a large sample including a lot of background events, but some component would only be explained by including astrophysical sources. In IceCube, one of the best ways of reducing background noise is to look for events traveling up through the Earth, since only neutrinos can pass through the Earth. We could also look at high energies, since backgrounds like atmospheric neutrinos fall off exponentially with energy. So we thought the first diffuse astrophysics signal would come from the high-energy tail of an upgoing sample.

After that, we expected to resolve the diffuse sample into some clusters, and after a few of the clusters remained consistent, to declare them astrophysical sources.

What we did instead was to skip to the end of this story. We found astrophysical neutrinos first, and then a diffuse upgoing signal only two years after that (just this past spring). The exciting part about finding this recent diffuse signal isn’t that it’s the first detection of astrophysics, or even the strongest. It’s exciting because it follows the story we thought neutrino astronomy was going to follow.

The first detection was exciting too. That used a different kind of analysis: we identified only a few events (28 in two years) that were extremely likely to be from astrophysical sources. These were so special that each one got a name, using the theme of the Muppets, from Sesame Street and the Muppet Show. One is named Bert, one Ernie, one Mr. Snuffleupagus, one Oscar the Grouch. If we keep analyzing our data this way and eventually get enough events, we can expand to the Muppet Babies cartoons and various muppet movies, even including things like Labyrinth that used Jim Henson’s talents but not the muppets specifically. I’m personally a big fan of the muppet naming scheme, partly because it draws from a cannon recent enough that it includes several women and many kinds of diversity. When naming events is our biggest problem, it will be a great day for neutrino astrophysics. For formal publications, we usually say “HESE” for “High Energy Stating Event,” instead of “muppets.”

The two bedrock assumptions of the muppet analysis were that (1) we’re the most interested in the highest energy events, and (2) the events must have started within the detector; they must be “contained.” That containment requirement means that they must have been neutrinos and not cosmic rays, since comic ray showers contain lots of stuff besides neutrinos that arrives at the same time. We can assume at the highest energies that no cosmic ray could make it through the outer layers of our detector without leaving a trace (unpacked: cosmic rays must leave a trace) but at lower energies some cosmic ray muons can steak through. For the first muppet analysis, we get around this by just looking at the highest energies.

This is backwards from what we expected in two ways: first, the sample we get is mostly from neutrinos coming from above the detector, and second, there are almost no background events in our sample, so we don’t have to include directional clustering to know that we’ve seen astrophysics.

The sample is mostly downgoing because the highest energy neutrinos are blocked by the Earth. Higher energy neutrinos are more likely to interact than low-energy neutrinos; it’s the opposite of our momentum-based intuition from faster cars slamming through walls without stopping. It’s a popular trivium that neutrinos can pass through lightyears of lead without interacting, but that’s only true at low energy scales like the neutrinos from nuclear reactors. At IceCube astrophysics scales, it takes only our tiny planet to stop a neutrino. So the muppet events we do see are mostly ones that don’t pass through the Earth.

Since the muppets sample has almost no background events (at the very most, 10 of the 28, but we don’t know which 10), we don’t need to do a clustering analysis. Traditionally, we thought this was the most promising way to find neutrino point sources, and the background would be neutrinos from interactions in the Earth’s atmosphere. But at PeV energies, there aren’t enough atmospheric neutrinos to explain what we saw, so each event in the new analysis is potentially as interesting as a cluster would be in the old analysis.

We haven’t yet seen clusters using the old techniques, and when we do, it will probably be celebrated by a small party, an email around our collaboration, some nights out for the people involved, and a PhD for someone (or a few someones). But it won’t be the same cover-of-Science-Magazine celebration (that was Mr. Snuffalupagus on the cover) and press coverage that we had for the first discovery. It will be a quiet victory, as it was for the recent diffuse result.

While it doesn’t have to follow the script we expect it to, science can still sometimes choose to follow a familiar plotline. And we are comforted by the familiarity.


Greetings from the South Pole

Saturday, December 31st, 2011

As a new Quantum Diarist, I wanted to introduce myself and my research work. And say hello from the bottom of the world. I am at the South Pole Station working on a new neutrino experiment called ARA, the Askaryan Radio Array.

This project is a second generation effort to look at the the highest-energy (GZK) neutrinos using radio detection of the coherent (Askaryan) emission from showers in dense materials. We’re building at the South Pole to take advantage of the largest block of dense, radio-transparent media on Earth, the 3km thick ice sheet that covers the continent. This is my second summer season at Pole working on ARA, last year we installed an engineering detector that has operated quite successfully throughout the year and now we’re installing the first production detector station. Ultimately we’re aiming for a detector array covering about 100 square kilometers with the antennas capable of detecting signals down to the bedrock below. A truly large detector. It’s much larger, but optimized for higher-energy events, than the IceCube detector completed last summer season at the Pole.

ARA is built on the experiences of the ANITA balloon-borne radio neutrino detector and the ice-drilling and radio spinoff efforts (RICE, AURA, & SATRA) of the IceCube experiment. It’s a small collaboration but with most of the world experience in radio neutrino detection and a significant block of the experience in hot-water drilling down into the ice. The main goal are the so-called GZK neutrinos, neutrinos produced by the interaction of the highest energy (charged particle) cosmic rays with the 3K microwave background radiation. More on all these physics topics in future postings…right now mostly wanting to say hello.

It’s New Year’s Eve at the South Pole. There are about 240 people here at the US South Pole Base, Amundsen-Scott Base, living and working in the new elevated station, or in the many small smaller building around the area. Some folks here are fairly traditional astronomers, working on the 10m South Pole Telescope, others have magnetometers, aurora cameras, seismometers, air sampling gear, and other scientific pursuits. The majority of people at Pole are here in support roles, driving heavy equipment, cooking dinner, washing the dishes, managing the cargo flow, and staffing the communications facility. Tonight there will be four bands performing, followed by a DJ set. We get satellite network a few hours per day and I’ll post this in the morning, in the new year for us.

Physics has gotten me to a lot of interesting places, and this is certainly way up there on that list, though it’s not the first project that had gotten me to Antarctica. I had worked on the CREAM and ANITA balloon experiments, both of which have flown from McMurdo Base on Ross Island just off the coast of Antarctica. (It’s probably close enough to count as Antarctica.) My background is in cosmic rays, I worked on spacecraft isotopic measurements of the cosmic rays while I was a graduate student at the University of Chicago. As a postdoc at Penn State, I worked on the HEAT balloon experiment measuring cosmic ray antimatter and the Pierre Auger Observatory in the Argentine grasslands. Later as a professor at the University of Minnesota, I added CREAM (a cosmic ray elemental abundance balloon experiment) and ANITA (the balloon neutrino experiment parent of the current ARA work). Now I am at the University of Wisconsin at Madison working on ARA, IceCube, and the HAWC TeV gamma-ray observatory currently under construction in Mexico. Detectors and their associated hardware are as important to me intellectually as the physics now.

So, greetings from the South Pole, a good place to do physics. And I’m looking forward to sharing my corner of the world of astroparticle physics with you, my dear readers.


A cosmic ray shower.

Editor’s note: Bob’s most excellent particle detector adventure, part 7.

Bob Peterson continues to travel with his QuarkNet particle detector around the edge of Africa recording remnants of cosmic rays. This offers a chance to study how cosmic ray recordings differ on land and sea and at different latitudes. The data will be accessible to high school students and teachers in several countries who use similar detectors to learn about particle physics.

Read his previous posts here: The voyage begins, Turning the detector on, Other science on the sea, Particle detectors don’t like light, Enduring a branding for science A teaching moment on the ocean.

11 May 2011
R/V Polarstern
Latitude: 30-56.1 N
Longitude: 14-27.0 W
off the Moroccan coast
Ship course 017° T
Ship velocity 10.8 knots

10 May:
Dawn; the forecast called for a sunny day? What’s that cloud bank out my cabin window? Oh, wait, that’s land! Ah, the Canary Islands right on schedule just as the navigator predicted, and we approach Las Palmas harbor from the south.

The Polarstern receives the pilot at 0945 (he’s late), and the ship proceeds cautiously into the slip. Forty-five minutes later, dock lines are thrown and we are winched tight to the quay and the gangway lowered.

We are here to receive new scientists from Alfred Wegner Institute, or AWI, coming onboard for special training in echo acoustics and bottom profiling. And it gives some of us a chance to feel land. Shore leave is two hours; be back by 1400 or the captain will not be happy. So, I escape. Sure enough the land is moving in a wave-like motion. I must have sea-legs.

Underway again at 1745. The pilot was late again. By 1830, the Canary Islands are falling behind and slipping into the sunset haze.

How IceCube works. Credit: IceCube collaboration

11 May:
Daily, the Polarstern weather technician, Klaus, launches a weather balloon for upper-atmosphere soundings. Michael Walter, my contact from DESY/IceCube, needs these data. I’m intrigued, so Klaus gladly offers to train me to ready and launch the balloons. This will be fun.

All over the world, weather stations and ships launch these balloons simultaneously, and they need to be at 10 kilometers, or 6 miles, altitude by 1200 Coordinated Universal Time, or UTC. So, Klaus prepares and launches the balloon one hour before because it takes that long to reach 33,000 feet. The balloons are filled with helium to about five feet diameter and carry a small data collection transponder called a radiosonde.

Launchings on land are straight forward; the technician steps out of the filing garage and let’s go. On ship, it’s anything but simple. The deck is pitching and rolling, the forward speed sweeps the deck with maybe 35 knots of wind, and the tall crow’s nest in the center of the ship is definitely in the way. There will be no end of grief from the crew if I hang the balloon there. So, Klaus coaches (and laughs) as I learn to manage the recalcitrant, reluctant object, but I’ve now mastered the preparation and launch. Launchings are analogous to a young boy throwing a rock off a cliff; except, it defies gravity. What fun to watch it sail away. I wonder how long I can still see it before it disappears into the haze.

The data returns to the ship in one-second intervals, showing the profiles of atmosphere parameters. The soundings return data on altitude, pressure, temperature, humidity and wind speed and these data might couple to the QuarkNet cosmic ray muon detector (CRMD) data. Michael Walter will use this to correlate to the cosmic ray flux, or flow rate of cosmic ray remnant particles passing through various areas of the sky. I hope that QuarkNet students can do the same. I, too, will return home with the large data sets to compare to the onboard QuarkNet detector.


*Quay: Pronounced “key”. A concrete, stone or metal platform lying
alongside or projecting into water for loading and unloading ships. Similar to a

*Pilot: a master mariner hired by the captain to guide a big ship into confined harbors. They have special local knowledge and training. Still the ship’s captain is ultimately responsible. A pilot job is nice if you can get it, because all have to wait for the pilot. They are notoriously late.

*Winch: A hauling or lifting device consisting of a rope, cable or chain winding around a horizontal, rotating drum, turned by a crank or by a motor or other power source.

*AWI: Alfred Wegner Institute – Research facility that owns and manages the R/V Polarstern.

*UTC: Coordinated Universal Time

*Radiosonde: An instrument carried by balloon or other means to various levels of the atmosphere and transmitting measurements by radio.

*Crow’s nest: A shelter or platform fixed near the top of the mast of a vessel as a place for instruments or lookout.

–Bob Peterson


Bob Peterson continues to travel with his QuarkNet  particle detector around the edge of Africa recording remnants of cosmic rays. This offers a chance to study how cosmic ray recordings differ on land and sea and at different latitudes. The data will be accessible to high school students and teachers in several countries who use similar detectors to learn about particle physics.

His first post explains why he’s taking his science to the seas and how getting a detector on a boat sounds easier than it is.

–April 20: Breakfast at 0730 and you better be on time. The galley crew frowns on late comers and they clear the tables whether you are done or not. Other scientists have boarded in preparation of our departure. There is a group of atmospheric chemists studying particles that nucleate clouds. They had a gigantic shipping container lifted aboard last night, and spent the night setting up. They look a bit bedraggled. Soon, I will be too. I want to get the detector on the air before we depart. But, still, the cosmic ray muon detector sits on the cargo deck and I can’t carry it up seven flights of stairs.

Cosmic ray muon detector aboard ship. Credit: Fermilab

–April 20, 1200: It’s noon and finally the cosmic ray muon detector (in a box) is sitting in front of the ship’s weather office. My contact, Michael Walter, from the high-energy physics laboratory DESY/Zeuthen in Germany,  does outreach with students using cosmic ray detectors and is a collaborator on IceCube. He  previously installed his own detector. My detector will live directly above. By having two detectors of the same type we can double check data and also have a backup for when one of the detectors malfunction, which has happened at times on previous trips. The afternoon will be busy: assemble, plateau, capture data, record data.

–April 20, 1950: Didn’t quite make collecting data. The cosmic ray muon detector is alive and healthy and all counters plateaued. That means that the detector has hit the sweet spot where the photo multiplier tubes are recording the optimal amount of photons. Below that spot we would be missing valuable data and above it the data would get muddy. While all this is great, I lack a computer to record data. I need drivers installed to talk to the data acquisition system, and the computer I’m using doesn’t have drivers. No driver; no data recorded. I must have the data. I will work on this problem
Right now, the pilot has arrived to shepherd the R/V Polarstern out of Cape Town and underway. I will hide in the dark corners of the bridge and stay out from under foot.

— April 20, 2001: Much is going on. The gangway has been taken in, the springs are loosed and weare headed north and west. The pilot departs with the briefest of words. It’s dark and the Southern Cross constellation  is rising in the east; Orion is settling in the west. We clear the breakwater at 2020, and, oh my, what a westerly swell. The weather officer warned me: Be ready. I am not, and my stomach rolls over. It’s been 30 years since I have felt such a thing, and I’m as green as the wreaths of Christmas. It’s going to be an unpleasant night. Quickly I retire to my bunk.

–April 21AM: The Polarstern is a big ship, but it is getting pushed around by 6-to 8-meter swells. After all we are near the roaring forties winds and the dominate westerlies. The weather guys have quickly become my friends as they point out that this will pass soon enough as we enter the southeast trade winds.
But, I can’t wait. I have to get that cosmic ray muon detector data recorded no matter my condition. If you need friends, look to your weathermen, named Klaus and Max, and your systems administrator, named Felix. Installing the driver has proven problematic for the available Ubuntu machine. Felix enters with a brand new Mac: “Can you use this?” Within minutes, I have data sliding neatly into the open file, and now I can relax. Back to my bunk where I will spend the afternoon.

–April 21 PM: Klaus was right. Slowly the swell subsided and so did my constitution. I managed to attend dinner and felt better. Not great; just better. More good news: the cosmic ray muon detector is behaving.

— April 23: I’m managing many things now. I’ve figured out the meal schedule. I’ve learned who to go to with questions: Klaus and Max and Felix are always willing but steer clear of the cargo mate. He’d just as soon bite your head off. I’m always welcome on the bridge and Philipp is good at providing details. I know much of this, though I’m a bit rusty. It’s all coming back. And still the cosmic ray muon detector data flows. Good thing.

— April 23 PM: The crew relaxes with a movie and the bar is open. Everyone settles into the routine. Tomorrow is Easter. I will have to think about how to worship. I suspect I’ll be all alone about it.

— Bob Peterson


Related information:

You can follow the journey at:

You can e-mail Bob questions at [email protected]. Please send only text, no images.


*Galley: A ship’s kitchen.

*Bridge: The elevated, enclosed platform on a ship from which the captain
and officers direct operations.

*Springs: Dock lines

*Breakwater: A barrier built out into a body of water to protect a coast or
harbor from the force of waves.

*Swell: A slow, regular movement of the sea in rolling
waves that do not break.


Bob Peterson has agreed to forfeit a month of his time and his non-sea-loving stomach, for a briefer period, in the name of science.

Bob Peterson

This Fermilab employee and QuarkNet instructor will shepherd a cosmic ray muon detector through rolling ocean waves around the edge of Africa to gather data to help the world’s largest frozen particle detector, the IceCube neutrino observatory at the South Pole. The detector is the same type as those built and used by high school students in cosmic ray study projects, including QuarkNet program, which allows students throughout the world to collect and share particle physics data. QuarkNet gives students a chance to interact with physicists and get a taste of what it would be like to work on a global experiment such as IceCube.

IceCube serves as a neutrino telescope peering at neutrino particles that cascade out of collisions of high-energy cosmic rays with the Earth’s atmosphere. The trick is that IceCube only wants to look at these cosmic neutrino remnants coming from a certain direction, from the opposite hemisphere and through the Earth, not those falling directly overhead of the detector.

The data Peterson collects will help IceTop, a smaller detector set a top IceCube, to give the most precise data to the IceCube collaboration so that it knows it is focusing on the right particles. His data will be combined with data collected on a similar trip last year in Antarctica by a group of Wisconsin college physics students. This combined data will tell researchers the varying intensity levels of cosmic ray remnants as you travel from the equator to the poles. This will help the IceTop collaboration calibrate its detector to compare data to IceCube and help IceCube reject background particles from downward cosmic ray remnants that can obscure the detectors’ views of neutrinos moving upward through the Earth.

Sketch of the IceCube detector. Each cross on the surface represents two IceTop tanks. Credit: IceTop Collaboration

Studying neutrinos in one of the coldest places on Earth will help scientists get a better picture of where high-energy neutrinos originate and how they contribute to the universe’s most violent events, exploding stars called supernovaes. These explosions spit out the heavy elements necessary for the creation of life on Earth. Without these neutrino-fed explosions the universe would look very, very different.

And so Peterson, an avid sailor, who gets sea sick for the first few days of every journey, packed up his gear and headed out to learn about the universe and its most distant, violent objects by riding on a boat.

He is blogging his adventures in science and seafaring here at Quantum Diaries. A glossary of sailing terms will appear at the bottom of each post to aid readers.

23 Apr 2011, R/V Polarstern
Lat: 24-50.5S
Long: 9-42.7E
somewhere off the Namibia coast
Heading: 320degT
Speed: 12 knots

Bob’s Blog begins wherein Bob is on a voyage aboard a German research vessel to the Southern Hemisphere and discovering that using the Internet aboard a ship isn’t that simple.

–April 18: I had a really nice blog written yesterday, but the mail server timed out, and poof. No more. Then I found out from others that, oh yes, that happened to them, too. Well, I won’t do that again.

–April 19 AM: I arrived in Cape Town, South Africa, late Monday night after a 26-hour flight. The trip took me through Dulles Airport and then through Dakar across the Atlantic. I recommend South Africa Airlines; they are good with comfort and food. But still, there I was standing in CPT wondering who was picking me up. After a few nervous minutes, the driver for the ships’ agent, Randal, found me contemplating my next move. Ah, now I’m in good hands as we visit the immigration office where there is much stamping of documents.

I was somewhat foggy after such a long trip. Finding my ship proved not so simple because another ship on the quay was bunkering at the time of my arrival. But I finally made my way down the narrow quay to the gangway and the R/V Polarstern. My question, “Permission to board?” was met with a blank stare, and by then Randal was long gone so retreating was not an option. Just when I thought I would have to take my chances on the neighboring rust bucket (the one that was bunkering), the 2nd Mate, Philipp Gumtow, appeared welcoming me aboard; he took charge of the situation. Soon, I was surveying my cabin and eyeing a nice bunk.

–April 19: My wake-up alarm came from a departing tanker from the next quay over (not from the rust bucket). The traditional departure signal is one long blast, and they care not who is sleeping. Fine, I’m awake. Time for breakfast. Where’s the galley? I find it, and there I meet Philipp again. He tells me, “No, this table is reserved for crew; you sit over there at the science table”.  Ah, the world on the Polarstern is segregated: crew, officers, scientists. I think I fall somewhere in between. A ship is like a summer camp. It is all about procedures and everyone must abide or chaos ensues. The trick is find a friendly party that will explain those procedures before I step over the unseen boundaries. Tina was just that person. She is a biology grad student studying the effect of ocean warming on pelagic fish.

Then I try a quick tour of the ship, but within three turns of a corner I’m completely turned around. The Polarstern has seven decks connected by a central stairs and many doors with inscrutable labels all written in German. This is my handicap. Still, my exploration starts from my cabin to the galley and back and expands from there.

–April 19 AM: The Cape Town harbor sits at the bottom of the continent where 5,000-foot mountains loom. It shelters many ships bound for ports to the West, but not the East because of the threat of pirates. Cape Town traffic has increased as cargo is off loaded to rail and truck to avoid the east side of Africa, and likewise cargo is received for the journey west.

There are big ships here: tankers, container ships, general cargo, oil rigs, crew boats for the rigs and rust buckets. There are some tied to a remote pier called the graveyard. They will soon become target practice or cut up for scrap. One ship stands out; so I go ashore for pictures. With its many derricks and lots of deck plumbing, I want to get a closer look at the Peace in Africa. No kidding, that’s the name. Immediately a shore officer wants to confiscate my camera. “No way,” I say. Then I notice the owner: DeBeers. This ship mines the ocean bottom for diamonds; think Howard Hughes and magnesium nodules. Peace in Africa my foot. I beat a hasty retreat back to the safety of the Polarstern.

QuarkNet detector taken on ship. Credit: Fermilab

— April 19 AM: All the while, I’m wondering: Where is my cosmic ray muon detector? I ask Sonja who is the agent handling all the Polarstern logistics, whether she has seen it. She says that she will check and let me know.

— April 19 PM: Whoops, my first surprise. The money onboard is the euro……. I knew that, but they require cash. Now I’m in trouble; my credit card will do me no good. I must come up with cash; Sonja offers help and a driver to a downtown bank. But, this quickly goes bust as the banks refuse to exchange dollars for euros especially for someone on a ship. You must have an account and a permanent address. Hmmmm, I think they’ve been burned before? What to do?

–April 19 PM: Sonja has found my box. It’s in Cape Town. Closer, but still not onboard.

–April 19 PM: All ships use an agent for logistics and paper work. The Polarstern uses Meihizen International. They are skilled at problem solving, including my cash shortage problem, and they gladly offer help. First, I will retrieve South African rands from an ATM; then the agent will go to his bank for euros because he has permanent-resident status. My money goes from credit card dollars to rands to euros and I can feel a slice out of my funds at every step.

Still, the snafu gave me a tour of Cape Town and a genial meeting with the president of the agent company. He’s a sailor; I’m a sailor. We get along famously; I’m invited back for a cruise on his yacht. Nice yacht.

–April 19, much later PM: The day is getting late, and I learn we will depart at exactly 2000 (8 p.m.) on Wednesday with or without my cosmic ray muon detector. Sonja says the box is now at the agent’s office. It’s closer and will be delivered late afternoon. Sure enough, I see it come out of the delivery truck and get hoisted via the ship’s crane (I think: Please don’t drop it boys) to the receiving deck.

But, still I can’t have it. I am told that the cargo mate must verify the box on his manifest list. The officer will release it tomorrow morning.


*quay: pronounced “key”.  A concrete, stone, or metal platform lying
alongside or projecting into water for loading and unloading ships. Similar to a

*bunkering: fueling a ship.

*galley: kitchen

*manifest: A document giving comprehensive details of a ship, its cargo
and other contents, passengers,and crew for the use of customs officers.

— Bob Peterson