Measurement of the very forward inclusive jet cross section in pp collisions at $\sqrt{s}=13~\mathrm{TeV}$ with CMS

The measurement of very forward jets at $13~\mathrm{TeV}$ in proton-proton collisions with CMS is reported. Such jets, in particular when correlated to other objects, are the most sensitive probes of the small-x parton dynamics in the proton. In this paper we demonstrate the fundamental capabilities of jet reconstruction with CMS using the CASTOR detector at a pseudorapidity of $-6.6<\eta<-5.2$. The data is corrected for all detector effects and compared to model calculations. Models based on Gribov-Regge calculations tend to predict a slightly softer spectrum in contrast to PYTHIA tunes. The data indicates a spectrum more consistent with the shape predicted by PYTHIA, however, the data are compatible with all models within the experimental uncertainties.