Very forward inclusive jet energy spectra were measured with the CMS experiment at the LHC in proton-lead collisions, with a centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=5.02\,\mathrm{TeV}$. The measurement was performed using the CASTOR calorimeter, which measures in the pseudorapidity range $-6.6<\eta<-5.2$. The spectra, with the proton (p+Pb) or ion (Pb+p) towards CASTOR, are unfolded to the particle level and compared to predictions of various event generators. The p+Pb/Pb+p ratio of the spectra is also presented, for which the systematic uncertainties in the measurement are significantly reduced.
The event generators considered in this analysis are not able to describe any of the spectra in their full energy range. Deviations between data and the models in excess of two orders of magnitude are observed.