The Design and Performance of IceCube DeepCore (1109.6096v1)

Abstract: The IceCube neutrino observatory in operation at the South Pole, Antarctica, comprises three distinct components: a large buried array for ultrahigh energy neutrino detection, a surface air shower array, and a new buried component called DeepCore. DeepCore was designed to lower the IceCube neutrino energy threshold by over an order of magnitude, to energies as low as about 10 GeV. DeepCore is situated primarily 2100 m below the surface of the icecap at the South Pole, at the bottom center of the existing IceCube array, and began taking physics data in May 2010. Its location takes advantage of the exceptionally clear ice at those depths and allows it to use the surrounding IceCube detector as a highly efficient active veto against the principal background of downward-going muons produced in cosmic-ray air showers. DeepCore has a module density roughly five times higher than that of the standard IceCube array, and uses photomultiplier tubes with a new photocathode featuring a quantum efficiency about 35% higher than standard IceCube PMTs. Taken together, these features of DeepCore will increase IceCube's sensitivity to neutrinos from WIMP dark matter annihilations, atmospheric neutrino oscillations, galactic supernova neutrinos, and point sources of neutrinos in the northern and southern skies. In this paper we describe the design and initial performance of DeepCore.

• The paper presents the innovative design with a denser sensor array and enhanced PMT efficiency that lowers the neutrino energy detection threshold to 10 GeV.
• It outlines extensive Monte Carlo simulations that validate DeepCore’s effective background suppression by a factor of 10^5 and optimized triggering algorithms.
• The study highlights significant implications for neutrino oscillations, dark matter searches, and broader astrophysical investigations using improved low-energy measurements.

The Design and Performance of IceCube DeepCore

This paper provides a detailed exploration of the IceCube DeepCore, a low-energy neutrino detector that serves as a critical extension of the IceCube Observatory located at the South Pole. The primary objective of DeepCore is to substantially lower the energy threshold of IceCube measurements, thereby enhancing the sensitivity to neutrinos with energies as low as 10 GeV. This has significant implications for a variety of high-energy astrophysical phenomena and fundamental particle physics experiments.

DeepCore Design and Instrumentation

DeepCore operates as a high-density subarray within the larger IceCube detector. Its design optimizes sensitivity at lower energies through several interrelated strategies: a higher density of optical sensors, advanced photomultiplier tubes (PMTs) with increased quantum efficiency, and deployment at depths greater than 2100 meters within the polar ice. This strategic location capitalizes on the exceptional optical clarity of the ice at those depths, thus enhancing detection capabilities.

A significant feature of DeepCore is its enhanced module density, which is approximately five times that of the standard IceCube array. The increase in PMT quantum efficiency was realized using a new photocathode providing roughly 35% greater quantum efficiency. These technical innovations, combined with the spatial arrangement of DeepCore modules, afford unprecedented sensitivity to low-energy neutrino events.

Simulation and Performance Metrics

The paper describes extensive simulation efforts to characterize DeepCore's performance. The Monte Carlo simulations simulate particle interactions and detector responses, providing insights into triggering, filtering, and effective volume and area for potential neutrino events. DeepCore's SMT3 trigger, which activates with as few as three coincidental hits from low-energy muons or neutrinos, marks a significant software advancement in capturing low-energy phenomena.

The effectiveness of the trigger and associated filtering algorithms is quantified, with an accomplished reduction in background noise from cosmic-ray interactions by a factor of approximately $10^5$. These achievements highlight DeepCore's formidable ability to differentiate between genuine neutrino events and background noise, showcasing its enhanced sensitivity to weakly interacting massive particles (WIMPs), neutrino oscillations, and neutrinos from astrophysical point sources.

Implications for Neutrino Astronomy and Particle Physics

DeepCore's operational capability below 10 GeV opens new experimental horizons in both theoretical and experimental astrophysics and particle physics. The improved resolution for low-energy neutrinos uncovers fresh opportunities for investigating atmospheric neutrino oscillations and probing the neutrino mass hierarchy. Furthermore, DeepCore promises to expand research into potential sources of neutrinos, including active galactic nuclei, gamma ray bursts, and supernovae.

From a particle physics perspective, DeepCore's sensitivity to solar WIMP annihilations holds transformative potential in the search for dark matter, possibly allowing limits to be set below those achievable by present accelerators. As well, with its ability to analyze soft-spectrum neutrinos from southern sky sources, including exotic astrophysical events, DeepCore substantially broadens the scientific yield of the IceCube Observatory.

Conclusion

In summary, the DeepCore subarray represents a meaningful advancement in neutrino detection technology. The combination of its sophisticated detection hardware and software has demonstrated notable improvements in background suppression and signal sensitivity within the IceCube Observatory. Continued operation and data collection are likely to provide deeper insights into the phenomena that govern both our universe and the fundamental particles within it. Future developments could further optimize trigger algorithms and extend DeepCore's application to novel research areas, fortifying its role in the ongoing progression of neutrino astronomy and high-energy particle physics.