Low Energy Cosmic Ray Spectrum from 250 TeV to 10 PeV using IceTop

TL;DR

This paper extends the IceTop cosmic ray spectrum measurement down to 250 TeV, bridging the gap with direct measurements, and compares results with other experiments and models, revealing a bend around the knee region.

Contribution

Introduces a new low-energy trigger for IceTop, enabling measurement of the cosmic ray spectrum from 250 TeV to 10 PeV, filling a key observational gap.

Findings

Spectrum shows a bend around the knee region.

Consistent results with different hadronic interaction models.

Extension of spectrum measurement to lower energies.

Abstract

Using IceTop, the surface component of the IceCube Neutrino Observatory, the all-particle cosmic ray energy spectrum has been determined above a few PeV. The measured energy spectrum leaves a gap of more than a decade in energy to direct measurements by balloon and satellite experiments. In this analysis, we lowered the energy threshold of IceTop to 250 TeV, narrowing the gap between IceTop and direct measurements. In order to collect lower energy events, we implemented a new trigger that uses four pairs of infill stations for which the separation between stations is less than 50 m, compared to 125 m for the main array. The new trigger collects data from the entire array for events with hits on at least one infill pair. The low-energy extension of the all-particle cosmic ray energy spectrum using these IceTop events is measured and is compared with the energy spectrum from HAWC and other experiments. Air shower simulations with two different hadronic interaction models, Sibyll 2.1 and QGSJetII-04, are used in this analysis and an energy spectrum for each model is produced. Both measured energy spectra show a bend around the knee region.