Particle Physics in Ice with IceCube DeepCore

📝 Abstract

The IceCube Neutrino Observatory is the world’s largest high energy neutrino telescope, using the Antarctic ice cap as a Cherenkov detector medium. DeepCore, the low energy extension to IceCube, is an infill array with a fiducial volume of around 30 MTon in the deepest, clearest ice, aiming for an energy threshold as low as 10 GeV and extending IceCube’s sensitivity to indirect dark matter searches and atmospheric neutrino oscillation physics. We will discuss the analysis of the first year of DeepCore data, as well as ideas for a further extension of the particle physics program in the ice with a future PINGU detector.

💡 Analysis

The IceCube Neutrino Observatory is the world’s largest high energy neutrino telescope, using the Antarctic ice cap as a Cherenkov detector medium. DeepCore, the low energy extension to IceCube, is an infill array with a fiducial volume of around 30 MTon in the deepest, clearest ice, aiming for an energy threshold as low as 10 GeV and extending IceCube’s sensitivity to indirect dark matter searches and atmospheric neutrino oscillation physics. We will discuss the analysis of the first year of DeepCore data, as well as ideas for a further extension of the particle physics program in the ice with a future PINGU detector.

📄 Content

Particle Physics in Ice with IceCube DeepCore Tyce DeYoung for the IceCube collaboration Department of Physics, Pennsylvania State University, University Park, PA 16802, U.S.A. E-mail: deyoung@psu.edu Abstract The IceCube Neutrino Observatory is the world’s largest high energy neutrino telescope, using the Antarctic ice cap as a Cherenkov detector medium. DeepCore, the low energy extension to IceCube, is an infill array with a fiducial volume of around 30 MTon in the deepest, clearest ice, aiming for an energy threshold as low as 10 GeV and extending IceCube’s sensitivity to indirect dark matter searches and atmospheric neutrino oscillation physics. We will discuss the analysis of the first year of DeepCore data, as well as ideas for a further extension of the particle physics program in the ice with a future PINGU detector. Keywords: astroparticle physics; neutrino oscillations; dark matter

1. Introduction The IceCube neutrino telescope, now fully opera- tional at depths of 1450-2450 m below the surface of the Antarctic ice cap, was designed to detect high en- ergy neutrinos from astrophysical accelerators of cos- mic rays. Although the energy threshold of a large vol- ume neutrino detector is not a sharp function, the orig- inal IceCube design focused on efficiency for neutrinos at TeV energies and above. Recently, the IceCube col- laboration decided to augment the response of the de- tector at lower energies with the addition of DeepCore, a fully contained subarray aimed at improving the sensi- tivity of IceCube to neutrinos with energies in the range of 10’s of GeV to a few hundred GeV. This energy range is of interest for several topics related to parti- cle physics, including measurements of neutrino oscil- lations and searches for neutrinos produced in the anni- hilation or decay of dark matter. DeepCore consists of an additional eight strings of photosensors (Digital Optical Modules, or DOMs) com- prising 10” Hamamatsu photomultiplier tubes and as- sociated data acquisition electronics housed in standard IceCube glass pressure vessels. For most of the Deep- Core DOMs, the standard IceCube R7081 PMTs were replaced with 7081MOD PMTs with Hamamatsu’s new super-bialkali photocathode. These PMTs provide ap- proximately 35% higher quantum efficiency (averaged over the detected Cherenkov spectrum) than the stan- dard bialkali PMTs. Sited at the bottom center of the IceCube array, Deep- Core benefits from the high optical quality of the ice at depths of 2100-2450 m, with an attenuation length of approximately 50 m in the blue wavelengths at which most Cherenkov photons are detected in ice. Deep- Core also benefits from the ability of the standard Ice- Cube sensors to detect atmospheric muons penetrating the ice from cosmic ray air showers above the detector, allowing substantial reduction in the background rate by vetoing events where traces of penetrating muons are seen. Each DeepCore string bears 50 DOMs in the fidu- cial region, with an additional 10 DOMs deployed at shallower depths to improve the vetoing efficiency for steeply vertical muons. In addition to the new Deep- Core strings, the DeepCore fiducial volume for analysis includes 12 standard IceCube strings, chosen so that the fiducial region is shielded on all sides by a veto region consisting of three rows of standard IceCube strings, as shown in Fig. 1. The random noise rate of IceCube DOMs is quite low (around 500 Hz, on average) due to the low tempera- tures and radiopurity of the ice cap. This permits Deep- Core to be operated with a very low trigger threshold, demanding that 3 DOMs within the DeepCore fiducial region detect light in “local coincidence” within a pe- riod of no more than 2500 ns. The local coincidence cri- terion counts DOMs as being hit (i.e., having detected light) only if one of the four neighboring DOMs on a Preprint submitted to NIM A Proceedings of RICAP 2011 March 8, 2021 arXiv:1112.1053v1 [astro-ph.HE] 5 Dec 2011 Top View IceCube Strings HQE DeepCore Strings DeepCore Infill Strings (Mix of HQE and normal DOMs) DeepCore IC79 IC86 Dust Layer Side View DeepCore strings have 10 DOMs with a DOM-to-DOM spacing of 10 meters 50 HQE DOMs with a DOM-to-DOM spacing of 7 meters 21 Normal DOMs with a DOM-to-DOM spacing of 17 meters Figure 1: Schematic layout of DeepCore within IceCube. The shaded region indicates the fiducal volume of DeepCore, at the bottom cen- ter of IceCube, plus the extra veto cap of DOMs deployed at shal- lower depths to reinforce the veto against vertically-downgoing atmo- spheric muons. This schematic depicts both the DeepCore configura- tion used in 2010, when 79 IceCube strings were operational, and the final DeepCore layout and fiducial region used in the 2011 run. string (two above and two below) also registers a hit within ±1 µs. Most of the resulting 185 Hz of trig- gers are due to stray light from muons which simulta- neously satisfy the main IceCube trigger condition of 8 DOMs hit in local coincidence within 5 µs,

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