Electromagnetic tomography of radial flow in the quark-gluon plasma

We present a novel multimessenger approach to extract the effective radial flow of the quark-gluon plasma (QGP) by jointly analyzing thermal photon and dilepton spectra in heavy-ion collisions. A key feature of this method is that it circumvents the need for an unmeasurable reference -- the temperature extracted from the photon spectrum in the absence of flow -- by establishing a linear correlation between it and the dilepton-inferred temperature within a calibrated framework. By leveraging the complementary sensitivities of photons and dileptons, we define an effective radial flow observable that reflects early-time collectivity and expansion dynamics. We find that this observable exhibits a strong correlation with the spacetime-averaged radial velocity of the QGP, providing it with clear physical meaning as a measure of collective expansion. Together with previous results linking dilepton temperatures to initial QGP conditions, our work establishes a consistent framework for electromagnetic tomography of the QGP, offering direct access to its early-time dynamics.