The mesons were reconstructed in the two photon decay channel for pT from 0.5 and 1 GeV/c up to 200 and 50 GeV/c for pi0 and eta mesons, respectively. The high momentum reach for the pi0 measurement was achieved by identifying two-photon showers reconstructed as a single energy deposit in the ALICE electromagnetic calorimeter.
The nuclear modification factor (RpPb) was measured as the ratio of the cross sections in p-Pb and pp collisions normalized by the atomic mass number. Below 10 GeV/c, RpPb is found to be smaller than unity, while above 10 GeV/c, it is consistent with unity. The measurement is described by calculations over the full transverse momentum range, which include nuclear shadowing or parton saturation, and provides further constraints to the nPDF parameterizations for lower than about 5 GeV/c.