Gallas Torreira, AbrahamAaij, RoelAbellán Beteta, CarlosAckerley, TomAdeva Andany, BernardoAdinolfi, MarcoAfsharnia, HosseinAidala, ChristineAiola, SimoneAjaltouni, Ziad2025-12-292025-12-292022-04-07R. Aaij et al. Phys. Rev. Lett. 128, 1420040031-9007https://hdl.handle.net/10347/44778The production of prompt charged particles in proton–lead collisions and in proton–proton collisions at the nucleon–nucleon center-of-mass energy SQRT(sNN) = 5 TeV is studied at LHCb as a function of pseudorapidity (eta) and transverse momentum (pT) with respect to the proton beam direction. The nuclear modification factor for charged particles is determined as a function of eta between -4.8 < eta < -2.5 (backward region) and 2.0 < eta < 4.8 (forward region), and pT between 0.2 < pT < 8.0 GeV/c. The results show a suppression of charged particle production in proton–lead collisions relative to proton–proton collisions in the forward region and an enhancement in the backward region for pT larger than 1.5 GeV/c. This measurement constrains nuclear PDFs and saturation models at previously unexplored values of the parton momentum fraction down to 10^-6.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Fragmentation into hadronsRelativistic heavy-ion collisionsHadronsHadron collidersParticle production2290 Física altas energíasjournal article10.1103/PhysRevLett.128.1420041079-7114open access