CASTOR, acronym for Centauro And Strange Object Research, is a novel sampling, Cherenkov-type calorimeter, located at the very forward region (-6.6 < η < -5.2) of the CMS detector, at the Large Hadron Collider (LHC). Originally designed for the study of Strange Quark Matter (SQM) and the so called Centauro-type cosmic-ray events, the calorimeter serves as an experimental tool for a wide physics program, within the context of forward physics phenomena occurring for both p-p and Pb-Pb collisions at very high energies. Very low-x QCD, underlying events and multiple interactions characteristics, diffraction in the presence of a hard scale, centrality determination and exotic events in heavy-ion collisions, energy flow, as well as constraining cosmic ray shower models are the main physics topics where the CASTOR detector is expected to contribute, mostly.
The measurement of very forward low-pT jets is of primary importance to probe the low-x structure of the proton, with x the fractional momentum of the struck parton with respect to that of the incoming proton. In the low-x region, the strong rise of the gluon density is expected to be tamed by recombination processes, leading to a saturation of the gluon density. The observation of this effect, which is not included in the DGLAP evolution equations, would shed light on the asymptotic high-energy behavior of Quantum Chromodynamics (QCD).