Critical evidence for nucleon coalescence in heavy-ion collisions at 400 MeV per nucleon

We present two critical pieces of evidence for the coalescence of nucleons in heavy-ion collisions at 400 MeV per nucleon. The elliptic flow parameters of the proton and of the helium isotopes plotted as functions of the transverse momentum overlap each other when scaled by the number of nucleons. In addition, the shapes of the invariant spectra of deuterons can be reproduced by the proton spectra powered by the number of constituent nucleons. By using the density-matrix formalism, we extract the rapidity-dependent source radius of the excited zone at chemical freeze out. The source radius is maximum at midrapidity, and it decreases towards the target and projectile rapidities. The estimated chemical freeze-out radius at midrapidity is about 20 % larger than the radius of the incident nuclei.