Conjectured α=0.5 at the QCD critical endpoint

Establish whether the Lévy stability exponent α of the pion-emitting source equals 0.5 at the quantum chromodynamics (QCD) critical endpoint of the phase diagram, as conjectured in femtoscopy analyses using symmetric Lévy sources and two-pion Bose–Einstein correlations.

Background

The paper measures the Lévy exponent α in Ar+Sc collisions at several SPS energies using two-pion femtoscopic correlation functions fitted with a symmetric Lévy source model. The authors reference a conjectured benchmark value α≈0.5 associated with the QCD critical endpoint and compare their observations against this value.

Their results yield α values between 1.5 and 2.0, significantly above the conjectured α≈0.5. The conjecture serves as a physics target connected to critical phenomena and the universality class expectations (e.g., 3D Ising), making its verification an open problem relevant to locating and characterizing the QCD critical endpoint.