Introduction to Cosmic Ray Physics with the IceCube Neutrino Observatory

The IceCube Neutrino Observatory at the geographic South Pole, completed in December of 2010, is not only a world-class neutrino observatory but is also an excellent instrument to study cosmic rays. IceCube includes multiple detector components, as shown in Figure 1. The IceCube-InIce array consists of 86 strings buried beneath the surface of the Antarctic ice sheet to a depth of 2500 m. Below a depth of 1500 m, these strings are instrumented with 60 digital optical modules (DOMs) apiece [1]. The DOMs are designed to detect the Cherenkov light emitted by charged particles traversing the ice [2]. The strings are arranged in a triangular grid with ∼125 m separation, as shown in Figure 2. Each IceCube-InIce string is topped with two ice-Cherenkov tanks separated by 10 m. These two tanks are referred to as a station, and all the surface stations together comprise the IceTop array [3]. Each tank is viewed by two DOMs apiece, one running at low gain, the other at high gain, to maximize the dynamic range.

Both the IceTop and IceCube-InIce DOMs are fully integrated into the data acquisition system of the observatory.

Observation Modes for Cosmic Ray Studies Using IceTop and IceCube-InIce

Since the IceTop and the IceCube-InIce arrays can be operated independently or in coincidence, there are a number of different cosmic ray studies that can be performed utilizing those three possible observation modes. We begin with a discussion of each observation mode: the analyses are discussed in the next sections. * e-mail: karen.andeen@marquette.edu

Studies using the IceTop Array alone

As discussed in [3], when six tanks in three stations register a signal in coincidence, the IceTop surface array is triggered and the signals from all tanks and the deep-ice detectors are preserved. IceTop data from each air shower event are then reconstructed using a maximum-likelihood procedure to fit the shape and normalization of a lateral distribution function (LDF) of the deposited charges. This reconstruction algorithm takes into account arrival time fluctuations and results in the fitted shower core position (x, y, z), direction (θ, φ), and (S 125 , β) . Here, β is related to the slope of the LDF, while S 125 is the "shower size" parameter, the result of the LDF fit to the signal strength measured in vertical equivalent muons (VEM) at a reference distance of 125 m perpendicular to the shower axis, as shown in Figure 3. At this distance, the shower size