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Search for Kaluza-Klein gravitons in extra dimension models via forward detectors at the LHC

We investigate contributions of Kaluza-Klein (KK) graviton in extra dimension models to the process $pp \to pγp \to pγj X$, where a proton emits a quasireal photon and is detected by using the very forward detectors planned at the LHC. In addition to the $γq$ initial state as in the Compton scattering in the standard model, the $γg$ scattering contributes through the $t$-channel exchange of KK gravitons. Taking account of pileup contributions to the background and examining viable kinematical cuts, constraints on the parameter space of both the ADD (Arkani-Hamed, Dimopoulos and Dvali) model and the RS (Randall and Sundrum) model are studied. With 200 fb$^{-1}$ data at a center-of-mass energy of 14 TeV, the expected lower bound on the cut-off scale for the ADD model is 6.3 TeV at 95% confidence level, while a lower limit of 2.0 (0.5) TeV is set on the mass of the first excited graviton with the coupling parameter $k/\overline{M}_{\rm Pl}=0.1$ (0.01) for the RS model.