Study of forward physics in sqrt(s_NN) = 8.1 TeV proton-Lead ion collisions with the LHCf detector at the LHC

The LHCf detectors were installed for the first time 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 (eta > 8.4) in proton-proton (p+p) and proton-ion (p+A) collisions. Until now the experiment has achieved successful measurements for p+p collisions at sqrt(s) =900 GeV, 2.78 TeV, 7 TeV and 13 TeV and for p+Pb collision at sqrt(s_NN) = 5.0 TeV. These data will be extremely useful in the near future for the calibration of hadronic interaction models that are commonly used for the study of the development of Extensive Air Showers (EAS) produced by extremely energetic cosmic-rays (CR) interacting with the atmospheric gas. Even though the most frequent collisions of cosmic ray protons in atmosphere involve mainly nitrogen and oxygen nuclei, the study of both the p+p and p+Pb systems at the LHC allows providing important information for the calibration of hadronic interactions models. A marked reduction of cross section values in p+A interactions with respect to p+p collisions, due to nuclear screening effects, has been observed in previous measurements performed at the RHIC accelerator at lower values of pseudo-rapidity and energy with respect to LHCf, and confirmed by LHCf at the LHC energy in the first p+Pb run at the beginning of 2013. The last upgrade of the LHC, followed by the successful p+p run at 13 TeV, could allow now producing p+Pb collisions at sqrt(s_NN) = 8.1 TeV. In this case the equivalent energy of the colliding protons in the laboratory frame (i.e. the frame at rest with respect to the target Lead nuclei) would be approximately 3 times greater than the highest ever reached before, thus representing a significant opportunity for our collaboration and hadronic model developers. For this reason we propose to install one of the LHCf detectors for the p+Pb run that is under discussion for 2016, with the goal of reaching a better understanding of the nuclear effects in a pseudo-rapidity and energy configuration that is very significant for CR physics and never investigated before.