5.8 Trillion Degrees: Getting to the Bottom of When the Smallest Meson Melts

A meson named bottomonium forms at low temperatures from a bond between a heavy bottom (b) quark and an anti-bottom quark. Under extreme temperatures, bottomonium may disintegrate. Source: Brookhaven National Laboratory

Research calculations reveal that a pair composed of a bottom quark and its antimatter equivalent, forming bottomonium mesons, need temperatures surpassing 5.8 trillion degrees Celsius to dissolve. This discovery brings clarity to the lower number of bottomonium particles seen in high-energy collisions at the Large Hadron Collider in comparison to the Relativistic Heavy Ion Collider. It also opens new prospects for investigating quark-gluon plasma attributes.

The Research

Theory specialists conducted computations to estimate the temperature that could cause bottomonium mesons to disintegrate. These mesons, one of the six quark varieties, comprise a heavy bottom quark tied to its antimatter counterpart – an antibottom quark. Bottomonium mesons appear in multiple states, including loosely bound, tightly bound, and very tightly bound – the smallest form of bottomonium meson. The study shows that even under extremely high temperatures, the smallest bottomonium particles remain stable and only break down under extreme conditions.

The Influence

The results provide a potential reason why fewer bottomonium particles are detected in high-energy ion collisions at the Large Hadron Collider (LHC) compared to the Relativistic Heavy Ion Collider (RHIC). The LHC particle accelerator is located at CERN in Europe, while the RHIC is a user facility of the Department of Energy at Brookhaven National Laboratory. Both facilities facilitate collisions of atomic nuclei that can melt protons and neutrons to release the inner quarks and gluons. However, the resulting quark-gluon plasma (QGP) might not be hot enough to fully dissolve bottomonium. Despite this, the collisions can still generate bottomonium particles, albeit in smaller numbers. This theoretical insight could foster the exploration of bottomonium melting as a means to study QGP properties.

The Study

To uncover the melting point of bottomonium states in quark-gluon plasma, scientists from Brookhaven Lab, the Homi Bhabha National Institute in India, and Humboldt-University in Berlin calculated meson correlation functions. These functions denote the interaction between the quark and antiquark constituting bottomonium. The researchers utilized powerful supercomputers and lattice quantum chromodynamics (QCD) to model the interactions in one spatial dimension. They observed that this correlation function experiences an exponential decay in spatial separation. This decay rate links to the screening mass, which relates to the binding energy between the bottom quark and the anti-b quark. The dependency of this screening mass on temperature differs based on whether the heavy quark and anti-quark are bound within a meson or move independently in QGP as an unbound pair (like when the meson has melted).

The lattice QCD calculations demonstrate that only when the temperature exceeds 5.8 trillion degrees Celsius do the screening masses behave in line with the predictions for an unbound b quark and anti-b quark. Therefore, the tiniest bottomonium (five times smaller than a proton) only melts at this temperature. It’s improbable that these temperatures can be reached in heavy ion collisions at RHIC, and only momentarily achievable in heavy ion collisions at LHC. This might explain the noticeable yield of bottomonium at both RHIC and LHC.

This research, titled “Bottomonium melting from screening correlators at high temperature” by Peter Petreczky, Sayantan Sharma, and Johannes Heinrich Weber, was published on 24 September 2021 in Physical Review D. DOI: 10.1103/PhysRevD.104.054511. The research received funding from the Department of Energy Office of Science, Nuclear Physics program.

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More about Bottomonium Melting Temperature

• Large Hadron Collider
• Relativistic Heavy Ion Collider
• Brookhaven National Laboratory
• Homi Bhabha National Institute
• Humboldt-University in Berlin
• Department of Energy Office of Science
• Bottomonium melting from screening correlators at high temperature – Research Paper