The activity in the field of diffractive physics at the Large Hadron Collider has been constantly increasing. This includes the planning for additional dedicated apparatus -- horizontal forward proton detectors. This work focuses on the problems rela
ted to the alignment of such devices. The effects of the misalignment of the detectors on their geometric acceptance and on the reconstruction of the proton kinematics are studied. The requirements for the alignment precision are inferred for different types of possible measurements.
A process of Central Exclusive $pi^+pi^-$ production in proton-proton collisions and its theoretical description is presented. A possibility of its measurement, during the special low luminosity LHC runs, with the help of the ATLAS central detector f
or measuring pions and the ALFA stations for tagging the scattered protons is studied. A visible cross section is estimated to be 21 $mu$b for $sqrt{s}=7$ TeV, which gives over 2000 events for 100 $mu$b$^{-1}$ of integrated luminosity. Differential distributions in pion pseudorapidities, pion and proton transverse momenta as well as $pi^+pi^-$ invariant mass are shown and discussed.
