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Title: Existence and location of the QCD critical point
Plain: 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: 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.
Settled by: A first-principles calculation reaching $\mu_B/T > 3$, or an experimentally established nonmonotonic fluctuation signal reproduced by dynamical critical-point modeling.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: open
Status 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.
Posed since: 1989