Infrastructure upgrade underway at IceCube

– We are going to put 700 new optical modules in those holes. These will include improved sensors which can collect more light and calibration devices which will help us to better understand the ice in our detector. The sensors will also be placed closer together, which will help lower the energy of the neutrinos we can detect.

– This is the first time that we are really upgrading the detector in all this time since we've been running.

Why are you doing this upgrade right now?

– When we first built IceCube starting in 2004, it was really a new experiment and we were not sure what we would see. We wanted to see how it would work, and if the neutrinos could be detected at the level we expected. We have been doing great science for the last 15 years and so it took a while before we felt like we needed to upgrade it. With this new development, we can see a bit lower energy events which can maybe let us see new classes of neutrino emitters. It'll also help us to improve our measurement of neutrino properties.

­– And at the South Pole, there's only really a few months of time you can get out and do anything. Right now, it’s summertime in the South Pole which is really the time when you can go out and drill.

What are neutrinos and why they are so interesting to measure?

– A neutrino is a neutral, nearly massless particle – kind of like an electron with less mass and no charge. Our universe is filled with neutrinos, in fact they are the second most common particle after photons. Neutrinos are really interesting because they pass through matter without interacting very much. This makes them difficult to detect, but when you do manage to capture them it means you can see inside very dense and extreme systems in the universe.

What are the benefits of placing a neutrino telescope at the South Pole, and what have you been able to discover so far?

– The South Pole is an ideal location for this type of detector. Because neutrinos interact only rarely, detecting them requires an enormous volume of material. The Antarctic ice provides both the necessary scale and optical clarity to observe the faint light produced when neutrinos interact in the ice. As a result, a detailed understanding of the ice is essential: how light passes through it directly affects our ability to determine a neutrino’s direction and energy. Improving this understanding is a central goal of the calibration devices included in the detector upgrade.

– IceCube discovered the diffuse flux of high-energy astrophysical neutrinos and has since identified three sources: the blazar TXS 0506+056 (a blazar is a very compact, extremely bright, and rapidly variable galactic nucleus, editor’s note), the active galaxy NGC 1068, and emission from Milky Way itself. In addition, the detector enables searches for new physics at energies and over distances far beyond what can be probed in terrestrial experiments.

Among the new optical equipment being inserted into the ice are also cameras of Swedish origin – how come?

– Sweden has a long history in IceCube. We were one of the founding members of AMANDA, which was the precursor experiment to IceCube. Sweden built a third of the optical modules that went into IceCube, but another specialty of Sweden is building cameras. We built a camera for the original IceCube detector and now there are seven Sweden cameras going down into the ice with this upgrade.

­– The cameras have light sources on them and that will allow us to directly view the ice and see what it looks like with our eyes, so maybe we can connect some features that are visible with the camera with what we detect in calibration. This effort is funded by the Swedish Research Council and the work was done here at Uppsala University and at Stockholm University.

With the new equipment installed, what do you hope you will be able to detect?

– We are installing all seven strings in this year – really between right now and January. I'm hoping that we can see new sources of neutrinos at lower energies. Improved understanding of the ice allows us to reanalyze 15 years of data and opens the door to discovering new high-energy sources.

– We will also improve our ability to measure the copious number of neutrinos from our atmosphere which allows us to make measurements of the properties of neutrinos themselves. In this way, we are not only the world’s leading neutrino telescope, but also an increasingly powerful particle physics detector.

Anneli Björkman