better understand whether fragmentation processes are affected by the presence of the colored medium.

Previously published results on $\pi^0$ and $\eta$ production at PHENIX were obtained in symmetric heavy-ion systems such as ${\mbox{Au$+$Au}\xspace}$ and ${\mbox{Cu$+$Cu}\xspace}$  [@Adler:2006bv; @Adare:2008cg; @Adare:2008qa; @Adare:2008ad; @Adare:2010dc]. Contrarily to that, ${\mbox{Cu$+$Au}\xspace}$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV is the first asymmetric system of heavy nuclei studied at RHIC. Such collisions provide a different collision geometry from the one realized in symmetric systems. In central collisions the Cu nucleus is fully submerged in the Au nucleus, which results in the reduction of nucleon-nucleon interactions in the “corona" region [@Pantuev:2005jt] of the collision (see Fig. \[fig:cartoon\]). In semi-central ${\mbox{Cu$+$Au}\xspace}$ collisions an asymmetry of the nuclear overlap region is present along the axis connecting the centers of the interacting nuclei. These features make ${\mbox{Cu$+$Au}\xspace}$ collision system an important part of the systematic study of the final-state effects in heavy-ion collisions.

In this paper we present $\pi^0$ and $\eta$ meson $p_T$ spectra and nuclear modification factor measurements in ${\mbox{Cu$+$Au}\xspace}$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Data were collected in RHIC Year-2012 run with the PHENIX detector.

Data analysis
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![Cartoon showing and collisions with comparable . On panel (b) the overlap area is asymmetric, and 