First direct evidence of quark-gluon plasma seen in small nuclear collision
Scientists at the Relativistic Heavy Ion Collider (RHIC) have found new evidence that collisions of small nuclei with large ones can create tiny specks of quark-gluon plasma (QGP), a state of matter thought to have existed in the universe just moments after the Big Bang.
This discovery provides the first direct evidence of energy loss from energetic particles in these small collision systems, a key signature of QGP formation.
It was previously thought that only collisions of large nuclei, like gold, could generate enough energy to create QGP. This is because larger nuclei have more protons and neutrons, leading to more powerful collisions.
However, recent findings from RHIC’s PHENIX experiment challenge this assumption. The results suggest that even small collision systems can produce these primordial droplets.
Observation of jet quenching
“We found, for the first time in a small collision system, the suppression of energetic particles, which is one of two main pieces of evidence for the QGP,” said PHENIX Collaboration Spokesperson Yasuyuki Akiba.
By analyzing data from collisions of deuterons (a small nucleus) with gold ions, scientists observed a phenomenon known as “jet quenching.”
“Jets are created when a quark or gluon within a proton or neutron in one of RHIC’s ion beams collides intensely with a quark or gluon in the nuclear particles that make up the beam traveling in the opposite direction,” explained the scientists in a press release.
Jet quenching occurs when energetic particles produced in the collision lose energy as they interact with the QGP, similar to how an object slows down when moving through water.
Novel method to measure centrality
To accurately measure this energy loss, the research team employed a novel method to determine the centrality of the collisions or the degree to which the collision is head-on.
Utilizing “direct” photons, which are produced in the collision and unaffected by the QGP, as a reference, they were able to precisely compare the number of energetic particles produced with the number of photons.
This comparison provided a clear indication of energy loss and, consequently, QGP formation.
“When we use the direct photons as a precise, accurate measure of the collision centrality, we can see the suppression [in central collisions] unambiguously,” added Akiba.
This new finding provides further evidence that QGP can be created in smaller collision systems than previously thought.
Implications and future research
Scientists are now applying the same method to analyze other small collision systems, such as proton-gold and helium-3-gold, to confirm these findings.
“Ongoing analyses of PHENIX’s proton-gold and helium-3-gold data with the same technique will help to further clarify the origins of this suppression to confirm our current understanding or rule it out by competing explanations,” remarked Axel Drees, a PHENIX physicist from Stony Brook University.
“The next step will be to apply the same method to other small collision systems,” concluded the press release.
As per the scientists, this discovery regarding QGP will have a significant impact on our understanding of the early universe.
Source: Interesting Engineering
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First direct evidence of quark-gluon plasma seen in small nuclear collision