First indication of LPM effect in LHCf, an LHC experiment

The Large Hadron Collider forward (LHCf) experiment is dedicated to the measurement of very forward neutral particle production in the high energy hadron-hadron collisions at LHC. The aim of the experiment is to improve the cosmic ray air shower development models and its setup gives an important opportunity to directly measure the Landau Pomeranchunk Migdal (LPM) effect in heavy absorber. This work presents the analysis for LPM effect on data taken in 2010 and 2013 at sqrts = 7 TeV and sqrts_NN = 5.02 TeV respectively. We study the interactions of gamma, mainly produced by pi_0 decay, in one of the calorimeter pairs of LHCf. This is composed by 16 Tungsten layers as absorbers and 16 plastic scintillators for energy measurements (Arm2). We use three parameters to describe the mean shower profile with respect the photon mean energy. The results are compared with Epics MonteCarlo simulation with LPM active and inactive models, shows a first evidence of LPM effect.