University of Wisconsin-Madison

IC86-2016, or a new physics run for IceCube

The IceCube Lab at the South Pole collects data from over 5,000 light sensors. Around one terabyte (TB) of data is recorded every day, which is then filtered, cleaned, and sent to the north over satellite. Image: Sven Lidstrom, IceCube/NSF
The IceCube Lab at the South Pole collects data from over 5,000 light sensors. Around one terabyte (TB) of data is recorded every day, which is then filtered, cleaned, and sent to the north over satellite. Image: Sven Lidstrom, IceCube/NSF

“On behalf of the operations group, I’m happy to report that as of run 127950 on 2016-05-20, 20:38:47 UTC, we have started the IC86-2016 physics run.” With these words, every IceCuber learned that we were entering a new year of data for IceCube. The mail was sent by John Kelley, who manages the detector operations in IceCube.

But what makes a new physics run special when IceCube is already taking data 99% of the time every day of the year? Well, data samples are delivered to IceCube researchers for analysis in one-year blocks. When the IceCube Collaboration searches for cosmic neutrinos or measures neutrino oscillations, it uses at least one year of data. Sure, scientists may sometimes use two or more years of data, too, but they will never use 1.5 years.

The reason is that updates to the data-taking system as well as detector calibrations are done yearly and need to be taken into account when analyzing the data. “It’s exciting that after more than five years since the completion of IceCube, we’re still expanding the physics reach of the detector by deploying new trigger and filter algorithms,” said Kelley when talking about the start of the IC86-2016 physics run.

But before detailing the updates, let’s summarize the IC86-2015 physics run in three numbers: 8,810 hours of data, 99.8% detector uptime and 97.9% analysis-ready data, also called clean uptime. Take a look at the numbers of the 2014 run. Since detector performance is so high, continued improvements by the IceCube operations group yield only small changes now. Still, they provided an extra 52 hours of interesting astrophysical data. As you know, very high energy neutrinos are rare—very rare, in fact. So every hour counts!

So, now let’s talk about the updates implemented for this new physics run. Detectorwise, four new surface detectors, which were deployed during the 2015 polar season, are now fully integrated into the data acquisition system. “These add to the previous IceTop tanks and increase the efficiency to veto atmospheric background events when searching for astrophysically interesting events,” says Matt Kauer, who is the IceCube run coordinator. More surface detectors are planned for deployment in the upcoming seasons.

The IceCube team at the South Pole deploying the surface scintillation detectors. Image: Delia Tosi, IceCube/NSF
The IceCube team at the South Pole deploying the surface scintillation detectors. Image: Delia Tosi, IceCube/NSF

Also related to the surface component of IceCube, our team in Delaware developed a new IceTop trigger that has now been deployed. It uses the closely-spaced infill tanks at the center of the detector to detect low-energy cosmic ray air showers.  

Other important updates include targeting an improvement for multimessenger searches within the international astrophysics and astronomy community. The quality of the event selection for track-like neutrino events has been enhanced. The very high energy alerts, which use events that start within the detector and throughgoing tracks, are now based on better online reconstructions. IceCube is currently generating about one event alert each month and about four per day at lower energy thresholds.

More significant changes have been made to the optical and gamma-ray follow-up systems, which analyze neutrinos for clustering in space or time and send alerts to other telescopes in case of an interesting coincidence. These systems had previously run at the South Pole, "but this year, neutrino events are transferred to the northern hemisphere over an Iridium satellite link and are typically available for analysis within 30 seconds after they are recorded," describes Jim Braun, a software developer in the IceCube detector operations team. Advantages of analyzing these events using systems at UW-Madison include the ability to view sky maps in real-time, easier maintenance of analysis algorithms, and the ability to send alerts to other telescopes in a straightforward manner.

Still another interesting update is the new monopole filter, designed to search for hypothetical magnetic monopoles with moderate velocities (0.1 to 0.75 times the speed of light) and developed by our team in Wuppertal.

If the last run provided about 13 very high energy neutrinos detected—we have not yet looked at the data, but by now we know more or less what nature will provide us—the new efforts to improve IceCube contributions to multimessenger campaigns across experiments will boost their impact. “In order to track down the source of these astrophysical neutrino events, it’s important to get the information from these events in the hands of the scientific community as quickly as possible so they can quickly look for a counterpart signal in their telescopes,” explains Erik Blaufuss, who is the IceCube analysis coordinator.