When charm mesons form matters: tracking quark-gluon plasma temperature

In collisions of oxygen nuclei at the Large Hadron Collider, two types of charm mesons flow differently through the hot plasma created in the collision—but only if they form at different temperatures. The team used simulations to show that $D_s^+$ mesons freezing out at 1.2 times the critical temperature, while $D^0$ mesons form at the critical temperature itself, naturally explains ALICE detector measurements. This timing difference acts as a thermometer for the quark-gluon plasma.