Imprint of the atmospheric attenuation process on electron distribution in EAS
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The lateral density distribution (LDD) of shower particles in an extensive air shower (EAS) experiment is commonly approximated by a particular type of lateral density function (LDF). A standard perception is being used in air shower physics since long, according to which the LDD is assumed to be symmetric about the EAS axis, and the adopted LDF is adequate for the description of the LDD. However, the simulated electron density of a non-vertical EAS is asymmetric. In this work, such asymmetry in the LDD can be qualitatively explained as the atmospheric attenuation suffered by each shower particle. Quantitatively, the asymmetry can be roughly described in terms of a gap length (GL) between the EAS core and the center of the modified density pattern consisting of several equi-density ellipses. This study also validates the use of such a modeling of the atmospheric attenuation on the electromagnetic component in an EAS by investigating the so called GL in simulated density data. A modified LDF is proposed, based on these features of the simulated densities for the purpose of shower reconstruction in EAS experiments. The GL arises from attenuation effect is found to increase with the mass of the shower initiating particle. A different radial dependence of the local age parameter (LAP) is seen, if the modified LDF is applied to simulated electron densities. Primary cosmic-ray mass sensitivity of the LAP is also re-examined.
KeywordsSimulations Cosmic-rays Extensive air showers Lateral density distribution Atmospheric attenuation
PACS Nos.98.70.Sa 96.50.sd
RKD thanks the SERB, Department of Science and Technology (Govt. of India) for financial support under the Grant No. EMR/2015/001390.
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