Vortices unveil hidden difference between quark and nuclear matter

In the intricate realm of particle physics, the study of atomic nuclei unveils a fascinating journey from nucleons to quarks. Recent research, published in the journal Physical Review B, embarked on a quest to discern the fundamental differences between liquids of nucleons and quarks.

Under the intense pressure of high densities, atomic nuclei transform into a liquid composed of nucleons, which, in turn, reveals another layer of complexity as they dissolve into a quark liquid at even higher densities. The central question driving this investigation was whether the liquids of nucleons and quarks inherently differ.

Theoretical calculations from the study shed light on this enigma. While both types of liquids exhibit vortices when in rotation, quark liquids exhibit a unique characteristic – their vortices carry a “color-magnetic field,” analogous to an ordinary magnetic field. This distinctive feature is notably absent in nucleon liquids, serving as a discerning factor between the two.

The interaction between quarks and nucleons inside nuclei is governed by the strong nuclear force, characterized by a captivating property known as confinement. This enigmatic concept implies that scientists can only observe groups of bound quarks, never an individual quark in isolation. Describing or defining confinement precisely using theoretical tools has proven to be a formidable challenge.

The novel approach taken in this study, utilizing vortex properties to differentiate between quark and nucleon liquids, addresses the longstanding problem of confinement. It proposes a nuanced perspective – a precise sense in which dense quark liquids are non-confining, while nuclear liquids exhibit confinement.

The distinction between nuclear matter and quark matter, a question echoing through the annals of strong interactions and quantum chromodynamics (QCD), is further explored. Traditional viewpoints, rooted in the Landau paradigm for phase transitions, suggest an absence of distinction between nuclear and quark matter, casting doubt on the sharp definition of confinement in QCD.

Contrary to these established notions, the current research challenges the status quo by leveraging tools developed by physicists over the past four decades. These tools, capable of detecting topological transitions in materials beyond the constraints of the Landau paradigm, bring a fresh perspective to the study of QCD. The application of these tools reveals a distinct nature for quark matter compared to nuclear matter.

Representation of nuclear matter on the left and of quark matter on the right. The question mark alludes to the question of whether these liquids can be distinguished in a theoretically rigorous manner. Credit: Institute of Modern Physics and Srimoyee Sen, Iowa State University

The crux of the matter lies in comparing vortex properties in the two scenarios. A straightforward calculation unravels a key distinction – the vortex in quark matter entraps a color-magnetic field, an absence glaringly evident in nuclear matter. This groundbreaking result not only marks a departure from previous conclusions but also suggests that confinement in dense QCD can be rigorously defined. In essence, the study introduces a paradigm shift in our understanding of the intricate dance between quarks and nucleons within the tapestry of particle physics.

Source: US Department of Energy

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