Proposal for the LHC Run 3 Addressing Cosmic Ray physics with forward measurements in proton – proton and proton – light nuclei collisions at LHC

The LHCf experiment was originally designed to measure neutral particles produced at very high pseudo-rapidity (η > 8.4) in p+ p collisions at an energy of 14 TeV in the center of mass frame and in p+A collision. Since the first activities at the LHC in 2009, the LHCf detectors have taken data in different conditions involving proton and ions with different energies. The measurements carried out so far concern p + p collisions at √ s=0.9, 2.76, 7 and 13 TeV and p+ Pb collisions at √ sNN=5 TeV and 8 TeV. These cases correspond to proton collisions in the laboratory frame with an equivalent energy ranging from 1014 eV to almost 1017 eV, thus covering a large energy range which is significant for the study of the highest energy cosmic-rays interactions with the atmosphere. These data are extremely useful for the calibration of hadronic interaction models used for the study of the development of atmospheric showers, the so called Extensive Air Showers (EAS), produced by extremely energetic cosmic-ray (CR) particles interacting with the atmospheric gas. Because of the characteristics of these collisions, the study of the p + p system only at LHC is not enough to have a complete picture of the real processes going on in the Earth atmosphere, where interactions involve mainly nitrogen and oxygen nuclei. The dynamic of p + N collisions can differ in many important aspects with respect to the more simple case of p+p interactions. For example, a significant reduction in the cross section in p+A with respect to p+p collisions, due to nuclear screening effects, has been found in previous measurements performed at smaller values of pseudo-rapidity and lower energy than the LHC; this reduction has been later confirmed by LHCf itself by comparing p+ p with p+ Pb interactions. In this document we propose to install the LHCf detectors for the p+p run at √ s=14 TeV and for the eventual proton light ion run that is under discussion after the first year of the LHC Run3. The main purpose of this proposal is to get a better understanding of the nuclear effects in a pseudo-rapidity and energy configuration that is very significant for CR physics, with the aim to reduce the systematic uncertainties still present in the High Energy hadronic interaction models. As an additional by-product, we can extend at 14 TeV the measurements already carried out by LHCf at smaller center of mass energies; thanks to the improved DAQ system, which allows more than the double of the previous DAQ rate, and to a more sophisticated trigger scheme, allowing to operate at a luminosity 10 times higher than before, we can significantly increase the statistics of our measurements. This will give us the opportunity to measure also the spectra of neutral hadrons others than π0 very forward produced in the p+ p and p+Light Ion collisions.