Tiny subatomic fireballs created in particle smashers seem to have a built-in 'thermostat' that keeps their temperature the same no matter what.
March 26, 2026
Original Paper
Why the dilepton temperatures at the relativistic heavy ion colliders are constant, T ~ 290 MeV?
arXiv · 2603.24219
The Takeaway
Usually, pumping more energy into a system makes it hotter, but in massive collisions at the LHC and RHIC, the resulting plasma stays stuck at exactly 3 trillion degrees. This 'thermostat' behavior suggests a fundamental and unexplained limit to how hot this exotic form of matter can get before it stops responding to increased energy.
From the abstract
The STAR collaboration at RHIC (BNL) and the ALICE collaboration at LHC (CERN) published recently dielectron ($e^+e^-$ pair) spectra in the intermediate mass region (IMR), $M_{e^+e^-}$ = (1-3) GeV, which show a constant, i.e. energy-independent, emission temperature $T_{IMR}\simeq$ 287+-27 MeV, at all bombarding energies $\sqrt{s_{NN}}$ from 27 to 200 GeV. What causes this strange 'Thermostat' behaviour? Why the temperature is so small and constant, although the bombarding energy is increased by