[Paper Review] The IceTop experiment in 2010

Todor Stanev|arXiv (Cornell University)|Nov 8, 2010

Astrophysics and Cosmic Phenomena3 citations

TL;DR

The IceTop experiment at the South Pole, integrated with the IceCube neutrino detector, measures cosmic ray energy spectra and composition using air shower events detected by surface Cherenkov tanks and deep-ice muon signals. By analyzing vertical and inclined showers across 73 deployed stations (with full deployment to 1 km²), it determined the cosmic ray 'knee' at 3.1 ± 0.3 PeV, marking a spectral steepening from E⁻².⁷¹ to E⁻³.¹¹.

ABSTRACT

We present the current status of the IceTop air shower array on top of the IceCube neutrino detector that IceTop can use as a huge detector of TeV muons. We laos give a brief discussion of different types of air shower events that contain information on the spectrum and composition of the cosmic rays in a wide energy range.

Motivation & Objective

• To measure the cosmic ray energy spectrum and composition using surface air shower detectors and coincident deep-ice muon signals.
• To determine the position and properties of the cosmic ray 'knee' in the energy spectrum.
• To study the response of muon bundles in inclined showers and their energy loss in deep ice.
• To analyze low-multiplicity air shower events (3–4 station triggers) for composition-sensitive parameters in the 200–1,000 TeV range.
• To calibrate and correct for environmental effects such as snow cover and tank freezing dynamics.

Proposed method

• IceTop uses 1 m-radius plastic Cherenkov tanks with dual-gain digital optical modules (DOMs) to detect electromagnetic and GeV muon components of air showers.
• Each IceTop station consists of two tanks spaced ~10 m apart, with coincidental hits (hard local coincidences) triggering the system when six DOMs are active.
• Single hits (soft local coincidences) are recorded as muons, electrons, or gamma rays.
• The IceCube detector at 1,500 m depth measures muon energy loss in 1 km of clear ice, providing complementary energy deposition data.
• Monte Carlo simulations are used to model detector response, accounting for array size, shape, and snow cover effects.
• Shower reconstruction uses surface station geometry and InIce muon track information to determine core position, zenith angle, and primary energy.

Experimental results

Research questions

• RQ1 What is the precise energy and composition of cosmic rays at the 'knee' of the spectrum, around 3 PeV?
• RQ2 How do muon energy losses in deep ice differ between proton- and iron-initiated showers?
• RQ3 To what extent can low-multiplicity air shower events (3–4 triggered stations) provide reliable energy and composition estimates?
• RQ4 How do environmental factors like snow cover and tank freezing affect signal shape and detector calibration?
• RQ5 Can coincident IceTop and IceCube data improve the separation of air shower events from high-energy neutrino events?

Key findings

• The cosmic ray 'knee' was determined at 3.1 ± 0.3 PeV, with the spectrum steepening from E⁻².⁷¹ to E⁻³.¹¹.
• For a 10 PeV iron shower, 53 muons above 100 GeV reach the top of IceCube, compared to 22 for a proton shower.
• A 1 TeV muon loses 643 GeV over 1 km of ice, with iron showers showing stronger energy loss suppression due to lower average muon energy.
• Three- and four-station triggers correspond to narrow energy ranges: 10⁵.³ to 10⁵.⁵ GeV for protons and 10⁵.⁵ to 10⁵.⁸ GeV for iron, enabling composition-sensitive studies.
• Inclined showers with zenith angles up to 72.5° can still trigger IceTop and be reconstructed via muon bundle tracks in IceCube, with core position estimated within 50 m.
• The slow freezing of IceTop tanks (months at -25°C) is due to ice’s insulating effect and heat from water circulation pumps that remove air bubbles.