CAREER: Cosmic Ray Composition across Five Decades in Energy (50 TeV to 5 EeV) with the IceCube Neutrino Observatory

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This award is funded in part under the American Rescue Plan Act of 2021 (Public Law 117-2)For more than 100 years we have known that cosmic rays constantly bombard our atmosphere and affect our daily lives on Earth. Cosmic rays are thought to be produced in the far reaches of the universe in some of the most violent observed astrophysical processes. Yet key information regarding the processes of cosmic ray creation, acceleration, and propagation through the universe is lacking. However, candidate theoretical models have been developed that make testable predictions about cosmic ray parameters that are observable at Earth. To test these models, precise and accurate experimental measurements of the individual elemental spectra of cosmic rays are needed from a single observatory across a wide range in energy. This project seeks to advance knowledge of the energy-dependent cosmic ray composition in an important energy range that will connect direct methods of observation with indirect methods. Direct methods include experiments that measure the cosmic ray particles with a relatively high degree of precision. Indirect methods include experiments that measure the interactions of cosmic ray particles with either the atmosphere or ice deep below the South Pole. Indirect methods are more likely to record many more and much higher energy interactions than direct methods. These higher energy interactions are of continuing scientific interest to understand the highest energy astrophysical sources of the cosmic rays. The current understanding of the energy-dependent cosmic ray composition has large uncertainties that will be reduced when the direct and indirect methods can be cross calibrated resulting in a significant advance in the field. The project will also focus on science education associated with cosmic particles, especially with historically under-represented groups in and around Milwaukee WI. In addition, the project will help improve intercultural competence (ICC) within the Principal Investigator's (PI's) university and within the scientific collaborations involved.The project will utilize three individual detector elements at the South Pole: IceAct (two recently deployed prototype air Cherenkov detectors), IceTop (near surface intra-ice optical sensors), and IceCube (deep ice cubic km array of optical sensors) with a goal to measure the cosmic ray composition over 5 decades of energy from ~50 TeV to ~5 EeV. Of particular technical note, this research will allow for event-by-event mass composition of interacting cosmic rays rather than treating data with a statistical approach. The proposal outlines three objectives, each leading to publication, divided into subtasks of research conducted by the Principal Investigator and a newly supported postdoctoral researcher. The research involves new simulation and the development of new data analytic tools and techniques. Objective 1 involves improving beyond a preliminary level the IceAct / IceCube reconstruction, calibration, and analysis towards an indirect measurement of the cosmic ray composition over the energy range that connects and allows comparisons with direct measurements by experiments that detect and precisely measure the cosmic particles. Objective 2 involves improving the PI's previous work on cosmic ray composition at higher energies using IceTop / IceCube with an increase of precision. Objective 3 is to determine the cosmic ray composition over the broad energy range using two methods: Combining the results of Objectives 1 and 2 and a combined global analysis of IceAct / IceTop / IceCube data and simulation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.