Measuring Extreme Temperatures in Quark-Gluon Plasma

Measuring temperatures in environments where no instrument can survive has been a significant challenge for scientists for a long time. However, a team of scientists at Brookhaven National Laboratory in New York has overcome this challenge by studying thermal electron-positron pairs released during rapid collisions of atomic nuclei in the Relativistic Heavy Ion Collider (RHIC).

Opening a New Thermal Window

Quark-gluon plasma is a unique state of matter where quarks and gluons exist freely rather than being confined within particles. The behavior of this plasma heavily depends on temperature. Until now, scientists lacked the tools to observe this hot, rapidly expanding system without compromising the results.

With quark-gluon plasma reaching temperatures of several trillion kelvin, the challenge was to find a “thermometer” capable of monitoring it without interference. Thermal lepton pairs, or electron-positron emissions produced throughout the plasma’s lifespan, emerged as ideal candidates.

Experimental Breakthrough at RHIC

To achieve this, the team enhanced the detectors at the Relativistic Heavy Ion Collider to isolate low-momentum lepton pairs and reduce background noise. The idea was tested that the energy distribution of these pairs could directly reveal the plasma’s temperature.

The researchers managed to obtain highly precise measurements despite the challenges of distinguishing true thermal signals from unrelated processes. The results showed two distinct thermal phases, depending on the mass of the emitted electron-positron pairs.

Distinct Temperature Phases

The results indicated that the thermal average in the low mass range reached about 2.01 trillion kelvin, aligning with theoretical predictions and temperatures observed when the plasma transitions to ordinary matter.

In the higher mass range, the thermal average was about 3.25 trillion kelvin, representing the initial and hottest phase of the plasma. This variation suggests that low-mass electron-positrons are produced later in the plasma’s evolution, while high-mass electron-positrons originate from the initial, more active phase.

Mapping Matter Under Extreme Conditions

By accurately measuring the temperature of quark-gluon plasma at various stages of its development, scientists obtain crucial experimental data to complete the “quantum phase map,” which is essential for mapping how fundamental matter behaves under extreme heat and density, similar to conditions moments after the Big Bang and found in cosmic phenomena like neutron stars.

Conclusion

Through this innovative research, scientists have opened a new window into understanding the early universe and its thermal conditions. This advancement represents not just a measurement, but the beginning of a new era in exploring the most extreme aspects of matter.