Particle production at forward rapidities in proton-nucleus collisions provides access to the target structure at very small momentum fraction x, where non-linear QCD dynamics is expect to play an important role. Recently, the CASTOR calorimeter at CMS , covering pseudodapidity region -6.6 < eta < -5.2, has released first jet spectra measurements in proton-lead collisions, probing nuclear structure down to Bjorken-x values of the order of 10^(-6).
In this talk, based on Ref we investigate the forward-jet energy spectrum within the Color Glass Condensate framework, focusing on the kinematic range covered by the CMS-CASTOR calorimeter. We show that our saturation-model calculations are compatible with the CASTOR measurements and that to optimally reproduce the data, effects of multiparton interactions need to be included on top on non-linear QCD dynamics. We predict a significant nuclear suppression — reaching down to 50% at the lowest considered jet energies E_jet∼500 GeV.
 CMS Collaboration, JHEP 05 (2019) 043, arXiv:1812.01691 [hep-ex]
 H. Mäntysaari, H. Paukkunen, Phys.Rev. D100 (2019) no.11, 114029, arXiv:1910.13116