[Paper Review] The modeling of the nuclear composition measurement performance of the Non-Imaging CHErenkov Array (NICHE)

John Krizmanic, D. R. Bergman+1 more|arXiv (Cornell University)|Jul 15, 2013

Astrophysics and Cosmic Phenomena3 citations

TL;DR

This paper models the nuclear composition measurement performance of the Non-Imaging CHErenkov Array (NICHE) using 4- and 5-component cosmic ray composition models derived from J. Hörandel's poly-gonato framework. By simulating NICHE's $X_{\rm max}$ and energy resolution, event statistics, and unfolding techniques, the study demonstrates that NICHE can resolve composition components with less than 15% uncertainty for fractions above 5% from $10^{15.8}$ to $10^{17.8}$ eV, enabling robust cross-calibration with TALE.

ABSTRACT

In its initial deployment, the Non-Imaging CHErenkov Array (NICHE)will measure the flux and nuclear composition of cosmic rays from below 10^16 eV to 10^18 eV by using measurements of the amplitude and time-spread of the air-shower Cherenkov signal to achieve a robust event-by-event measurement of Xmax and energy. NICHE will have sufficient area and angular acceptance to have significant overlap with TA/TALE, within which NICHE is located, to allow for energy cross-calibration. In order to quantify NICHE's ability to measure the cosmic ray nuclear composition, 4-component composition models were constructed based upon a poly-gonato model of J. Hoerandel using simulated Xmax distributions of the composite composition as a function of energy. These composition distributions were then unfolded into individual components via an analysis technique that included NICHE's simulated Xmax and energy resolution performance as a function of energy as well as the effects of finite event statistics. Details of the construction of the 4-component composition models and NICHE's ability to determine the individual components as a function of energy are presented.

Motivation & Objective

• To quantify NICHE's ability to measure cosmic ray nuclear composition across the $10^{15.8}$ to $10^{17.8}$ eV energy range.
• To assess how NICHE's $X_{\rm max}$ and energy resolution performance translates into composition resolution for multi-component models.
• To enable cross-calibration between NICHE's Cherenkov measurements and TALE's fluorescence measurements via overlapping event statistics.
• To develop a computationally tractable 4- and 5-component model that preserves astrophysical sensitivity while reducing complexity.

Proposed method

• Constructed 4- and 5-component cosmic ray composition models based on J. Hörandel's poly-gonato model, grouping elements into proton, helium, CNO, silicon, and iron components.
• Used CORSIKA simulations to generate energy-dependent $X_{\rm max}$ distributions for each composition model across third-of-a-decade energy bins from $10^{15.8}$ to $10^{17.8}$ eV.
• Incorporated NICHE's simulated $X_{\rm max}$ resolution (<40 g/cm² at $10^{16}$ eV, improving with energy) and energy resolution (<15% at $10^{16}$ eV) into the simulation framework.
• Applied Monte Carlo techniques to generate composite $X_{\rm max}$ distributions with Gaussian fluctuations based on 2-year statistics and 10% duty cycle.
• Unfolded the composite distributions using a 4-component model (p, He, CNO, Fe) to retrieve component fractions, repeating 100 times to assess mean and RMS deviations.
• Compared reconstructed fractions to true input compositions to evaluate accuracy and resolution across energy bins.

Experimental results

Research questions

• RQ1 Can NICHE resolve a 4-component cosmic ray composition model with sufficient accuracy across the $10^{15.8}$ to $10^{17.8}$ eV energy range?
• RQ2 What is the uncertainty in NICHE’s reconstructed composition fractions for components above 5% in fractional abundance?
• RQ3 How does NICHE’s $X_{\rm max}$ and energy resolution performance translate into measurable composition sensitivity?
• RQ4 To what extent can NICHE provide cross-calibration with TALE’s fluorescence measurements above $10^{17}$ eV?
• RQ5 How do finite statistics and resolution effects impact the fidelity of composition unfolding in NICHE?

Key findings

• NICHE can reconstruct cosmic ray composition components with less than 15% uncertainty for fractional abundances above 5% across the $10^{15.8}$ to $10^{17.8}$ eV energy range.
• The 5-component model (p, He, CNO, Si, Fe) shows excellent agreement with the full poly-gonato model, validating the compression approach for simulation efficiency.
• At $10^{17}$ to $10^{17.5}$ eV, NICHE achieves approximately 700 all-particle events in the galactic-only model and 1200 in the galactic+extragalactic model over two years, enabling meaningful composition analysis.
• Above $10^{17.5}$ eV, statistics drop to ~170 events in the galactic+EG model, but the analysis remains feasible due to high resolution and unfolding robustness.
• The $X_{\rm max}$ resolution of NICHE is better than 40 g/cm² at $10^{16}$ eV and improves to under 20 g/cm² above $10^{16.5}$ eV, enabling precise event-by-event $X_{\rm max}$ reconstruction.
• NICHE’s performance allows for reliable cross-calibration with TALE’s fluorescence measurements above $10^{17}$ eV, ensuring consistency between Cherenkov and fluorescence techniques.