Simulation of Direct Photon Production in $${d+d}$$ Collisions at $${\sqrt{s_{NN}}=13.5}$$ GeV and $${\sqrt{s_{NN}}=27}$$ GeV

The upcoming SPD experiment at the NICA collider will provide a detailed study of direct photon production in deuteron–deuteron and proton–proton collisions. Direct photons serve as a crucial tool for investigating the dynamics of interactions in high-energy nuclear collisions. In this paper we calculate direct photon invariant spectra and nuclear modification factors as a function of transverse momentum in the rapidity region $$\left|y\right|<3$$ at the energies of $$\sqrt{s_{NN}}=13.5$$ GeV and $$\sqrt{s_{NN}}=27$$ GeV. The measurements were performed using free proton PDFs and nuclear PDFs for the deuteron interactions. The small difference between them suggests that the nuclear effects in the nuclear PDF are weak. The suppression of direct photon production in deuteron–deuteron collisions compared to proton–proton collisions indicates that the isospin effect is a major contributor to nuclear effects.