Applications of S/S showers universality for mass composition and hadronic interactions studies

We present the first results of the application of the recently found universality of behavior of muon signal Sμ to electromagnetic (EM) signal Sem ratio with respect to the vertical depth of showers maximum Xv max for mass composition and hadronic interaction studies. Making use of the fact that for zenith angles > 45 degrees the dependence of Sμ/Sem on Xv max is very similar for QGSJET II and EPOS 1.99 we show that this provides the possibility to estimate muon shower content in almost interaction model independent way. To evaluate the excess of signal in the data in respect to Monte-Carlo predictions we propose to use mass independence of the electromagnetic signal. Using the simulations with EPOS 1.99 as a fake data we show that one can determine the absolute scaling factor between these fake data and the interaction model under test (QGSJET II in our case). Applying this scaling factor to the total and muon signals of QGSJET II one can make accurate conclusions on the primary mass of samples prepared with EPOS 1.99.