NUC In the literature: open

Existence and location of the QCD critical point

In plain words

At zero net baryon density, ordinary matter turns into quark-gluon plasma smoothly as it heats. At higher density the change may become abrupt, and the critical point is where smooth turns abrupt, if it exists.

Precise statement

Determine whether the chiral crossover line $T_{\mathrm{pc}}(\mu_B)$ ($T_{\mathrm{pc}}(0)$ about $156\,\mathrm{MeV}$, $\mu_B$ the baryon chemical potential) ends at a critical point (T_c, mu_B,c) beyond which the transition is first order, and locate it. Lattice QCD disfavors a critical point at $\mu_B/T$ below about 3. Answer: yes or no, and (T_c, mu_B,c) with uncertainty.

What would settle it

A first-principles calculation reaching $\mu_B/T > 3$, or an experimentally established nonmonotonic fluctuation signal reproduced by dynamical critical-point modeling.

Status in the literature

Unverified note

Functional-method and lattice-based extrapolations from 2021 to 2025 placed a possible critical point near $\mu_B$ of roughly 400 to 650 MeV, beyond direct lattice reach as of 2026.