Finite temperature lattice simulations of quantum chromodynamics (QCD) are sensitive to the hadronic mass spectrum for temperatures below the “critical” temperature $T_c\approx 160\mathrm{MeV}$. We show that a recent precision determination of the QCD trace anomaly shows evidence for the existence of a large number of hadron states beyond those known from experiment. The lattice results are well represented by an exponentially growing mass spectrum up to a temperature $T=155\mathrm{MeV}$. Using simple parametrizations of the hadron mass spectrum we show how one may estimate the total spectral weight in these yet undermined states.

• Received 19 August 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.252002