Searching for anomalous top quark interactions with proton tagging and timing detectors at the LHC

We study the LHC sensitivity to new broad neutral resonances produced in two-photon fusion and decaying to a top quark pair, γγ → tt¯. This is probed in central exclusive tt¯ production in proton-proton collisions, pp → ptt¯ p. We use the tagging of the intact protons by PPS (CMS) and AFP (ATLAS) and consider the semi-leptonic tt¯ channel. The sensitivity is also mapped onto a set of dimension-8 γγtt¯ operators in the large mass limit. Using the kinematical correlations between the intact protons and the reconstructed tt¯ system, we obtain a sensitivity to the couplings of the dimension-8 operators of 1.4 10⁻¹¹ GeV⁻⁴ at 95% CL. The sensitivity to the anomalous couplings is significantly improved down to about 7 10⁻¹² GeV⁻⁴ if the proton time-of-flight is known with a precision of 20 ps in future measurements. The 95% CL sensitivity to broad neutral resonances reaches masses of order 1500 GeV when using timing information.