The feasibility studies of the measurement of the central exclusive jet production at the LHC using the proton tagging technique are presented. In order to reach the low jet-mass region, single tagged events were considered. The studies were performe
d at the c.m. energy of 14 TeV and the ATLAS detector, but are also applicable for the CMS-TOTEM experiments. Four data-taking scenarios were considered: AFP and ALFA detectors as forward proton taggers and $beta^*$ = 0.55 m and $beta^*$ = 90 m optics. After the event selection, the signal-to-background ratio ranges between 5 and $10^4$. Finally, the expected precision of the central exclusive dijet cross-section measurement for data collection period of 100 h is estimated.
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 simple C++ class structure for construction of a Monte Carlo event generators which can produce unweighted events within relativistic phase space is presented. The generator is self-adapting to the provided matrix element and acceptance cuts. The p
rogram is designed specially for exclusive processes and includes, as an example of such an application, implementation of the model for exclusive production of meson pairs $pp rightarrow p M^+M^- p $ in high energy proton-proton collisions.
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.
The measurement of diffractively scattered protons in the ATLAS Forward Physics detector system placed 220 m away from the ATLAS interaction point is studied. A parameterisation of the scattered proton transport through the LHC magnet lattice is pres
ented. The proton energy unfolding and its impact on the centrally produced scalar particle mass resolution are discussed.
