Hadronic interaction studied by TA

Two studies by the Telescope Array group related to the hadronic interaction observed with Extensive Air Showers are reviewed. (1) Inelastic p-air cross section sigma(inel)(p-air) = 567.0 +/- 70.5 [stat](-25)(+29) [sys] mb and total p-p cross section sigma(tot)(p-p) = 170(-44)(+48) [stat](-17)(+19) [sys] mb were determined using the 5 years of TA hybrid data with one of the 3 FD stations. These results at the highest energy root s(NN)=95 TeV showed good agreements with the extrapolation from the previous measurements and model predictions. (2) The signal sizes of SD were compared between data and MC using 7 years of TA SD data in the energy range from 10(18.8) eV to 10(19.2) eV. It was found that the data/MC ratios exceed unity and the deviation becomes larger when the expected fraction of muon signal, defined as muon purity P, is higher. The results support the muon excess (with respect to MC) problem reported by the previous observations.