Speaker
Description
In Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA), an air-shower array designed for sub-PeV $\gamma$-ray observations in the Southern Hemisphere, the accuracy of primary energy reconstruction is a key factor that determines the energy spectrum of individual $\gamma$-ray sources.
In this study, we compare the performance of $\gamma$-ray energy estimators based on the lateral density parameter $S_{x}$, where $x$ is the shower core distance to be optimized, and the sum of particle densities, $\Sigma \rho$, using Monte Carlo simulations. By constructing energy conversion functions that take the zenith-angle dependence into account, we evaluate the energy resolution and bias from the distribution of $\ln(E_{\mathrm{rec}}/E_{\mathrm{true}})$.
We find that among the tested estimators, the lateral density parameter at 40 m ($S_{40}$) provides the best energy resolution. Within the $S_{x}$ family, $S_{40}$ outperforms larger core distances such as $S_{70}$; for example, in the 30--100 TeV range, the resolution improves from about 39% to 30%, corresponding to an improvement of about 5--10%. Compared to the sum of particle densities, $\Sigma \rho$, $S_{40}$ further improves the energy resolution from about 30% to 20%.
In this presentation, we discuss the details of each energy estimator and their performance. We will also discuss their impact on the determination of the $\gamma$-ray energy spectrum.
