Exploring the Frontiers of Cosmic-Ray Physics: Perspectives on GRANDProto300 and the GRAND Project

Abstract The Giant Radio Array for Neutrino Detection (GRAND) is an envisioned large-scale radio array designed to detect ultrahigh-energy cosmic rays (UHECRs, E &gt; 100 PeV) and neutrinos. Employing cost-effective radio antennas distributed across vast areas, GRAND is optimized to observe the rare flux of ultrahigh-energy particles with high precision. The GRANDProto300 (GP300) pathfinder array, currently under deployment, targets the 10 16.5 –10 18 eV range and is anticipated to achieve approximately 15% energy resolution and 20 g cm −2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>X</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> precision. This level of precision enables accurate measurements of the fine structure of the energy spectrum, mean logarithmic mass ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:mi>ln</mml:mi> <mml:mi>A</mml:mi> <mml:mo stretchy="false">〉</mml:mo> </mml:math> ), and proton flux within this energy range for GP300. After 5 yr of data collection, the sensitivity for detecting anisotropy could reach 5 × 10 −3 for energies below 10 17.1 eV. With its substantially larger effective area, GRAND extends these capabilities to the highest energies (∼10 20 eV), offering enhanced statistics and sensitivity for spectral, composition, and anisotropy measurements within 1 yr for UHECRs.