Internal gas target experiments at the LHC

The physics opportunities offered by a fixed-target program using the proton and lead-ion beams of the LHC is wide and exciting. The LHC beams can provide the most energetic fixed-target measurements by pp, pA, and PbA collisions at √sNN = 72–115 GeV probing unexplored regions of the kinematical plane, including the high-x region. In the case of an unpolarized target the physics rich ranges from QCD to astroparticle, while the polarized target option opens the ground to novel measurements of TMDs, thereby contributing with a complementary approach to the understanding of the dynamics of the quark-gluon interplay inside the nucleon up to the 3-dimensional description of the nucleons. Among the main LHC experiments LHCb is the most suitable to host a fixed gas target. A description of the ongoing fixed-target proposals aimed at having the first LHC unpolarized data in Run3 and polarized data in Run4 will be discussed.