Critical point remains elusive after measurements
Collisions between gold nuclei yield a striking clue, but no evidence of a new state of matter.
Researchers have found a striking dip in their measurements during the latest experiments at the American particle accelerator RHIC. It could fit with what is known as a critical point in dense nuclear matter, but other explanations remain possible.
The STAR collaboration studied collisions between gold nuclei at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider. The researchers examined changes in the momentum of the particles produced after such a collision.
The new analysis covers collision energies of 3 to 7.7 billion electronvolts. The researchers compared these with previously published STAR measurements up to 200 billion electronvolts. At lower energies, extremely dense nuclear matter forms, while at higher energies quarks and gluons behave more freely in a quark–gluon plasma.
The momentum fluctuations reached a minimum in the range of approximately 5.2 to 7.7 billion electronvolts. According to Brookhaven, the deviation from a smooth trend has a statistical significance of approximately five sigma. This means that the deviation is statistically striking within the chosen model, not that the researchers have already proved the underlying physical mechanism.
The measured momentum fluctuations serve as an approximation of temperature fluctuations in the short-lived mixture of particles. According to theory, such fluctuations can be suppressed near a critical point: a transition region where the way nuclear matter changes state shifts.
The research touches on a fundamental question in nuclear physics. Scientists are trying to determine how matter behaved shortly after the Big Bang and under conditions that may also occur inside neutron stars.
The STAR researchers stress that a single measured quantity cannot establish the presence of a critical point. A widely used transport model without a critical point does not reproduce the dip, but that does not rule out other explanations. New measurements and theoretical calculations are needed.
The result has been published in Physical Review Letters and is therefore part of peer-reviewed research. It is a clue in an ongoing search, not a confirmed discovery of a new phase or a breakthrough that replaces the existing picture.
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The article’s core has been checked against Brookhaven and an independent science source. The text distinguishes between statistical significance and a proven physical explanation.
- confirmed The STAR collaboration studied collisions between gold nuclei at RHIC. — Described by Brookhaven National Laboratory. source
- confirmed The analysis covers 3 to 7.7 billion electronvolts and compares them with data up to 200 billion electronvolts. — Mentioned in the research description. source
- confirmed The momentum fluctuations reached a minimum at around 5.2 to 7.7 billion electronvolts. — Reported by Brookhaven and Phys.org. source
- confirmed The deviation from a smooth trend has a significance of approximately five sigma. — Stated in the description of the STAR analysis. source
- confirmed The research has been published in Physical Review Letters. — Reported by Brookhaven National Laboratory. source
- confirmed The results do not prove that a critical point exists. — The researchers mention alternative explanations and stress that a single observable is not decisive. source
Editor's note
The research is peer-reviewed and the statistical deviation has been confirmed. The interpretation as a clue pointing to a critical point remains provisional and is not presented by the researchers themselves as proof.Sources
- RHIC Reports New Data from High-density Nuclear Matter — Brookhaven National Laboratory
- RHIC data reveal intriguing dip in momentum fluctuations in high-density nuclear matter — Phys.org
More on this in Dutch media
- de Volkskrant — „rhic star”
- RTL Nieuws — „rhic star”
- NOS — „rhic star”