A new basic air shower observable sensitive to the cosmic-ray elemental mass

Abstract Based on a Monte Carlo simulation study of vertical extensive air showers (EAS) at the KASCADE location we introduce a new simple observable η ρ (45;310) (in short η ρ ) - the ratio between two lateral electron densities of an EAS measured at two well-defined radial distances indicated by the characteristic radial feature of the local age parameter (LAP). Our analyses of simulated data generated by the Group I nuclei with cosmic-ray elemental masses, A actual = 1, 4, 12, 16, 24, 32, 40, 56, observed a double correlation of η ρ with, (i) the lateral shower age s av , and (ii) A actual of the EAS initiating primary particle. Applying the first correlation to a new set of simulated showers initiated by the Group II nuclei with A actual = 7, 14, 20, 28, 40, 52, the average difference between the lateral shower age s av obtained directly from the conventional LAP approach and the estimated one s est is found to be close to 0. The second correlation involving η ρ with A actual applied to the set of such showers estimates the average atomic 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:msub> <mml:mrow> <mml:mi>A</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">est</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> </mml:math> of their shower initiating primaries, utilizing the η ρ s. Results of the work revealed that the method of estimating the lateral shower age is almost high-energy interaction model-independent. A certain level of model dependence is albeit found in the case of <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:msub> <mml:mrow> <mml:mi>A</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">est</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> </mml:math> estimation.