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The study of high energy cosmic rays reveals subtle changes in the power law energy spectrum near 1015 eV (the `knee' of the energy spectrum). The changes are thought to arise from changes in source origin, acceleration mechanism limitations, or even confinement in the Galaxy. Each of these mechanisms has separate predictions for the change of the charge composition in the region of the knee. Previous measurements of composition not only suffer from poor charge resolution (δZ / Z ≥ 100-500%) but also have the unfortunate problem of being uncertain due to unknown particle physics interaction parameters at these energies. The result is a degenerate solution involving the particle physics model and the primary nuclear charge, adding further uncertainty in the astrophysical interpretation.
In this seminar I will review some of these recent measurements from the DICE and BLANCA experiments, and will describe the interaction model dependency of the interpretation of the results. I will then describe a new technique that can break the primary nuclear charge/particle physics degeneracy as well as provide high resolution measurments of cosmic ray charge (δZ / Z < 5%) in the region of the knee. In addition, this new technique may result in the reduction of background electron and proton events in ground-based TeV gamma-ray instruments as well as the first measurements of the electron energy spectrum around 1 TeV. The technique should also allow reliable measurements of utltra-heavy nuclei such as Pb, Zr, U as well as searches for `quark nuggets'. Finally, the techique will also allow direct measurment of the nuclear interaction cross-section and fragementation proceses at with a tagged charge beam at energies well above what can be achieved at man-made accelerators.
