Pis’ma v ZhETF, vol. 105, iss. 4, pp. 209 – 210 2017 February 25 c Effect of meson cloud on the jet nuclear modification factor in pA collisions B.G.Zakharov1) L.D.Landau Institute for Theoretical Physics, 117334 Moscow, Russia Submitted 12 December 2016 DOI: 10.7868/S0370274X17040026 Factorization of hard and soft process suggests that in the cross section of hard reactions the soft physics can be accumulated in parton distribution functions (PDFs) of colliding particles. <...> The correlations of this type have been observed in recent measurements by ATLAS [1] of the centrality dependence of the jet nuclear modification factor RpA for p+Pb collisions at √s = 5.02TeV. <...> The RpA for jet production is defined as RpA = where Njet pA and Njet dNjet pA/dpTdy NcolldNjet pA/dpTdy , (1) pp are the jet yields in pA and pp collisions, and Ncoll is the number of the binary collisions. <...> In [1] it has been observed that the jet nuclear modification factor RpPb in the broad (minimum bias) 0 − 90% centrality region is close to unity. <...> However, it is not the case for narrow centrality bins. <...> For high pT the RpPb has been found to be suppressed in central events (RpPb < 1) and to be enhanced in peripheral events (RpPb > 1). <...> The mechanism of [2] assumes that in the presence of an energetic parton (which is necessary for a hard process to occur) the number of soft partons in the projectile is suppressed. <...> It leads naturally to correlation of the jet RpA with the multiplicity/centrality. <...> Because, due to the nonperturbative physics of the underlying events (UEs), it is impossible to obtain robust predictions for the multiplicity/centrality dependence of RpA within the parton level schemes. <...> The meson cloud of the proton plays an important role in the flavor dependence of nucleon PDFs in deep inelastic scattering, and is probably responsible for the violation of the Gottfried sum rule [3]. <...> The emergence of the centrality dependence of RpA in the scenario with the meson cloud is conceptually very similar to the partonic mechanism of [2]. <...> It results in suppression of the UEs multiplicity in jet production at high pT , that should lead to centrality dependence <...>