Advances in understanding the quark substructure of scalars

Advances in understanding the quark substructure of scalars

Contour plot of function F(sr,si) [defined in (55)]. The point where F=0 represents the first physical isovector scalar meson pole and gives the properties of a0(980). Credit: European Physical Journal C (2022). DOI: 10.1140/epjc/s10052-022-11103-4

At this stage in the universe’s evolution (about 14 billion years after the Big Bang), there are four fundamental forces in action that cause interactions between the constituents of matter.

One of these forces is gravity which, for example, keeps us revolving around the sun and allows us to enjoy the four seasons. Another is the electromagnetic force that benefits us every day. From the light bulb that we turn on every night to the dynamics of the electrons inside our electronic devices, they are all driven by the electromagnetic force. The other two forces are not as often noticed in daily life, but this does not mean that they are less important.

These two forces are limited in the atomic nucleus (distances around 10-15 m or less) and are traditionally referred to as “nuclear forces.” One of them is the strong nuclear force (the strongest of all four forces) which is responsible for keeping the nucleus intact by binding its protons and neutrons together.

Without the strong nuclear force, nuclei would not form, we would not exist, and the sky would be empty. The other is the weak nuclear force which is responsible for transforming one nucleus into another and sometimes breaking them apart. We benefit from the effects of the weak nuclear force in our nuclear reactors.

The protons and neutrons are members of a large family of composite particles called hadrons, and they are all made of fundamental particles called quarks. The theory that describes the strong interaction between quarks is called Quantum Chromodynamics (QCD), according to which quarks engage in strong interaction by exchanging mediating particles called gluons.

This is similar to how fundamental charged particles participate in electromagnetic interaction by exchanging photons in the theory of quantum electrodynamics (QED). However, there are some major differences between QCD and QED, such as the fact that photons cannot form bound states, but gluons can in principle bind together to form composites called glue balls.

Theoretical understanding of the formation and interactions between glue balls and quark matter, as well as their experimental detection, are ambitious goals of formidable complexity. Despite several Nobel Prizes in Physics already awarded for the remarkable discoveries in particle physics related to QCD, some aspects remain open questions and have challenged theoretical physics for many decades. This problem is recognized by the Clay Mathematics Institute ( as one of the seven unsolved problems in mathematics, known as the Millennium Problems in Mathematics.

The main research of Amir Fariborz is on the strong interaction between quarks and their interactions with glue balls. Models developed by Fariborz and collaborators have been very successful in describing experimental data and have received notable citations in the literature. Additional information about Fariborz’s research can be found in the Inspire high energy physics literature database.

In this recent paper published in European Physical Journal C the generalized linear sigma model of QCD (developed by Fariborz et al) is used for the scattering of two special types of hadrons called pion (π) and eta (η). This spread is particularly important because it probes an intermediate composite state [called a0980] which are part of a family of hadrons called scalar mesons.

These composite particles of quarks play a special role in QCD by breaking a symmetry in the dynamical equations called chiral symmetry. Understanding the quark substructure of scalars sheds light on the strong interaction between quarks and gluons. This recent work has confirmed that the light scalar mesons contain a significant four-quark component, a feature that puts scalar mesons in the challenging category of exotic hadron spectroscopy.

More information:
Amir H. Fariborz et al, Chiral nonet mixing in pi-eta scattering, European Physical Journal C (2022). DOI: 10.1140/epjc/s10052-022-11103-4

Provided by Suny Polytechnic Institute

Citation: Advances in Understanding the Quark Substructure of Scalars (2022, December 23) Retrieved December 26, 2022, from

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