PROCEEDINGS OF THE 31 st ICRC, L ´ OD ´ Z 2009 1 Influence of the low energy hadronic interaction models on the secondary cosmic ray proton and antiproton fluxes at mountain altitude. Arunava Bhadra * , Sanjay K. Ghosh †‡ , Partha S. Joarder † , Arindam Mukherjee * and Sibaji Raha †‡ * High Energy & Cosmic Ray Research Centre, University of North Bengal, Siliguri, West Bengal, India 734013 † Centre for Astroparticle Physics and Space Science, Bose Institute, Block EN, Sector V, Salt Lake, Kolkata, India 700091 ‡ Department of Physics, Bose Institute, 93/1 A.P.C. Road, Kolkata, India 700009 Abstract. The influence of the low energy hadronic interaction models on the secondary cosmic ray proton and antiproton fluxes at mountain altitude has been examined using air shower simulation program CORSIKA. When the simulated results are compared with the recent precise measurements by the BESS spectrometer it is found that the model FLUKA describes the BESS observations on secondary proton spectrum better than the other two models, UrQMD and GHEISHA but FLUKA generated antiproton spectrum shows significant deviation from the BESS observation whereas UrQMD and GHEISHA repro- duce the BESS observations reasonably well. Keywords: EAS, Low energy hadronic interaction models, Proton and Antiproton flux I. I NTRODUCTION Monte-Carlo simulations of the extensive air shower is strongly dependent on our knowledge of the interaction mechanisms of energetic particles. Such knowledge on particle interactions is uncertain even at low (below ∼ 5 GeV) and intermediate (from few GeV to a few hundred GeV) energies as there is lack of data on hadron-nucleus interactions and almost no measurements are available for the particle production in pion-nucleus collisions. One relies mostly on theoretical models of particle interactions in such cases. The interaction models used in simulation programs are necessarily of the nature of extrapolations of known processes and/or of low energy accelerator data so that each of such models has its own parametrization guided by some (mainly QCD- motivated) theoretical prescriptions. Large uncertainities involved in these models influence the simulations of low to intermediate energy secondary cosmic ray flux in an EAS [1], [2], [3]. The aim of the present work is to examine the sensitivity of the low to intermediate energy secondary proton and antiproton fluxes on the relevant hadronic interaction models. The simulated showers of secondary protons, that arise from hadronic interactions of the forward kinematic region, are expected to be particularly responsive to the choice of interaction models. To gener- ate secondary fluxes for various models of hadronic in- teractions, the air shower simulation program CORSIKA (COsmic Ray SImulation for KAscade) version 6.600 [4] is exploited here that allows one to choose any of the three popular low energy hadronic interaction models, namely GHEISHA [5], FLUKA [6] and UrQMD [7], [8], respectively. We also use the model QGSJET 01 [9] for the description of hadronic interactions at high energies. The borderline between the high and the low energies is set as 80 GeV/n by default in this simulation program. Due to the steeply falling energy spectrum of the primary cosmic rays, the contribution of the primary particles with energies above 80 GeV/n on the secondary proton spectrum is found to be only about 15 percent. The high energy hadronic interaction models are, therefore, not likely to have much effects on the low energy secondary proton and antoproton spectrum. Whether the low energy interaction models of CORSIKA can be discriminated vis-a-vis actual measurements will also be examined in this paper by comparing the simulated secondary proton and antiproton spectra obtained from these models with the recent precise measurements of such fluxes at the mountain altitude,at an atmospheric depth of 742 g cm -2 , by the BESS spectrometer [10] A problem in differentiating the influence of hadronic interaction models is that the estimation of secondary fluxes through MC simulations include various system- atic errors caused not only by the built-in uncertainties in the interaction models but also by the errors involved in the estimation of values of various physical inputs, such as the primary cosmic ray fluxes, the atmospheric density profiles etc. The effects of such errors in the calculation of physical inputs considerably complicate the simulated flux in such a way so as to make it difficult to isolate out the influence of interaction models alone on the calculated values of secondary fluxes. In particular, a dominant systematic error in evaluating the flux of cosmic ray secondaries arises from the uncertainties involved in the estimation of input fluxes of the primary cosmic rays. To minimize such uncertainties, the simu- lated results of the primary cosmic ray energy spectra, as measured by the abovementioned BESS instruments [11], would be considered in this paper as the inputs in the simulations after taking into account the effect of solar modulation. The article is organized as follows: in the next