LHCf Letter of Intent for a p-Pb run. A precise study of forward physics in √s_NN= 4.4 TeV proton-Lead ion collisions with LHCf at the LHC

The LHCf detectors were installed in the TAN regions on both sides of IP1 at the beginning of the LHC run in 2009. The goal of the experiment is the measurement of neutral particle production at very high pseudo-rapidity values (η > 8.4) in proton-proton (pp) and proton-ion (pA) collisions. Until now data have been for two different physics cases, pp interactions at 900 GeV and 7 TeV center of mass energy. These data are extremely useful for the calibration of hadronic interaction models used for the study of the development of atmospheric showers, identified also as Extensive Air Showers (EAS), produced by extremely energetic cosmic-ray (CR) particles interacting with the atmospheric gas. Anyway the study of only the pp system in not enough to have a complete picture of hadronic interactions in atmosphere, where interactions involve mainly nitrogen and oxygen nuclei which can differ in important aspects with respect to the more simple case of pp interaction. A marked reduction of cross section values in pA interactions with respect to pp collisions, due to nuclear screening effects, has been found in previous measurements performed at lower values of pseudo-rapidity and energy than the LHC. Thus we propose to install one of the LHCf detectors for the p-Pb run that is under discussion for the 2012, with the goal of reaching a better understanding of these nuclear effects in a pseudo-rapidity and energy configuration that is very significant for CR physics.