The IceCube Neutrino Observatory is the world’s largest neutrino detector. In July 2018, we announced the discovery of the first likely source of ultra-high energy neutrinos, the blazar TXS 0506+056. The discovery was announced in two side-by-side articles in Science and received widespread press coverage. The first Science article, “Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A,” was co-authored by the IceCube Collaboration and 15 follow-up observatories. It describes the detection of a single high-energy astrophysical neutrino and the subsequent detection of (photon) counterparts by various telescopes. The second article, “Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert,” was authored by just IceCube and describes the detection of an excess of energetic neutrinos from the same source in our archival data. A popular-press article in The Conversation by Penn State’s Doug Cowen, Azadeh Keivani (now at Columbia U.) and Derek Fox, “The IceCube observatory detects neutrino and discovers a blazar as its source,” has received nearly 70,000 reads.
Additional press articles covering our detection appeared in the NYTimes, CNN.com, CBSnews.com, the Philadelphia Inquirer, Smithsonian Magazine, and Penn State News and Penn State ICS News, and was featured in Astronomy Picture of the Day on July 16, 2018.
The identification of TXS 0506+056 followed by several years our earlier discovery of ultrahigh energy astrophysical neutrinos. This earlier discovery garnered Physics World 2013 Breakthrough of the Year. The result was also published in Science as “Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector.” IceCube has now collected about 100 high energy neutrino candidates, as first described in the Physical Review Letters article “Observation of High Energy Astrophysical Neutrinos in Three Years of IceCube Data.”
IceCube is an extremely versatile instrument. With its DeepCore sub-array it can also perform world-class neutrino oscillation measurements. The Penn State group has contributed to measurements of muon neutrino disappearance and is now actively working on tau neutrino appearance using IceCube DeepCore. DeepCore’s measurement of muon neutrino disappearance places IceCube in the same league as the immensely successful Super-Kamiokande detector and numerous dedicated accelerator-based experiments. For more details, please see our paper in Physical Review D, Determining neutrino oscillation parameters from atmospheric muon neutrino disappearance with three years of IceCube DeepCore data. More recent analysis techniques will give us a factor of several improvement in statistics and promise to improve this result still further.
We are eager to build on IceCube’s success with the IceCube Upgrade and with “IceCube-Gen2,” both of which will enhance the detector’s sensitivity to both lower and higher energy neutrinos. Penn State is one of five US institutions that submitted the IceCube Upgrade proposal to NSF, focusing on the electronics for the new modules to be deployed in the ice, and on the primary analysis of the device, atmospheric tau neutrino appearance. As part of IceCube-Gen2, we also hope to build the Precision IceCube Next Generation Upgrade (PINGU), whose goal is to lower IceCube’s neutrino energy threshold to enable world-leading measurements of neutrino oscillation parameters using atmospheric neutrinos, including the “neutrino mass ordering,” one of the few remaining unknown fundamental parameters of the Standard Model of Particle Physics. With the high energy component of IceCube-Gen2, we plan to increase IceCube’s ultrahigh energy neutrino event rate by about a factor of 10 to better measure the spectrum of these mysterious particles, and to identify more of their sources.