Deciphering the Early Universe’s Mysteries – Proton Resonance Offers Fresh Perspectives

by Tatsuya Nakamura
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Proton Resonance

Physics research from the mid-20th century unveiled the phenomenon of proton resonance, yet a comprehensive understanding of the three-dimensional architecture of resonating protons remains elusive. Latest experiments conducted at Jefferson Lab contribute valuable data concerning the early universe and elementary particles like nucleons, composed of quarks and gluons.

Recent studies illuminate the three-dimensional configurations of nucleon resonances.

In the middle of the 20th century, scientific research revealed that protons could resonate, similar to how a bell vibrates. In the ensuing decades, advancements have generated three-dimensional representations of protons, substantially increasing our understanding of their structure in the ground state. Nonetheless, there is still a paucity of information about the three-dimensional organization of a resonating proton.

New experiments carried out at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility have further investigated the three-dimensional geometries of both proton and neutron resonances. This research adds another element to the complex understanding of the tumultuous, emergent universe existing shortly after the Big Bang.

Exploring the intrinsic qualities and behaviors of nucleons provides essential revelations about the fundamental constituents of matter. Nucleons are the protons and neutrons that constitute the atomic nuclei. Each nucleon is made up of three quarks, tightly connected by gluons through the strong force—nature’s most potent interaction.

A nucleon’s most stable, low-energy configuration is referred to as its ground state. However, when forcibly elevated to a higher-energy state, its quarks engage in rotational and vibrational motions, displaying a phenomenon termed nucleon resonance.

A research team consisting of physicists from Justus Liebig Universitat (JLU) Giessen in Germany and the University of Connecticut spearheaded the CLAS Collaboration’s effort to undertake an experiment exploring these nucleon resonances. The experiment was executed at Jefferson Lab’s state-of-the-art Continuous Electron Beam Accelerator Facility (CEBAF), a DOE Office of Science user facility supporting the investigative endeavors of over 1,800 nuclear physicists globally. The research findings have been recently documented in the highly esteemed peer-reviewed journal, Physical Review Letters.

Stefan Diehl, the analysis leader, indicated that the team’s research elucidates fundamental attributes of nucleon resonances. Diehl, a postdoctoral researcher and project leader at JLU Giessen’s 2nd Physics Institute and a research professor at the University of Connecticut, also pointed out that this work stimulates new inquiries into the three-dimensional structure of resonating protons and their excitation process.

“This represents the inaugural instance where a measurement or observation is sensitive to the three-dimensional properties of such an excited state,” Diehl stated. “Essentially, this is just the initial phase, and this measurement is inaugurating a new domain of research.”

The Enigma of Matter Formation

The experiment took place in Experimental Hall B between 2018 and 2019, employing Jefferson Lab’s CLAS12 detector. A high-velocity electron beam was directed into a chamber filled with cooled hydrogen gas. The electrons collided with the chamber’s protons, thereby exciting the quarks and inducing nucleon resonance in conjunction with a quark-antiquark state, known as a meson.

Although these excitations are transitory, they leave behind traces in the form of novel particles, originating from the dissipating energy of the excited particles. These new particles have a sufficiently long lifespan to be detected, enabling the team to reconstruct the resonance.

Diehl and his colleagues recently presented their findings at a collaborative workshop titled “Exploring resonance structure with transition GPDs” in Trento, Italy. The study has already prompted two theoretical groups to publish papers discussing the research.

Future experiments are planned at Jefferson Lab, utilizing various targets and polarizations. By dispersing electrons from polarized protons, the team aims to probe different aspects of the scattering mechanism. Furthermore, studying similar processes like the generation of resonance along with an energetic photon can yield additional vital data.

Diehl noted that such studies can help scientists deduce the properties of the cosmos shortly after the Big Bang. “Initially, the early universe contained only a high-energy plasma of quarks and gluons, all in a state of rotation due to the immense energy,” Diehl explained. “Eventually, matter began to coalesce, and the first entities to form were the excited nucleon states. As the universe continued to expand and cool, ground state nucleons became stable.”

“Through these research endeavors, we can glean insights into the characteristics of these resonances, which in turn could reveal how matter came into existence in the universe and why the universe persists in its current state.”

Reference: “First Measurement of Hard Exclusive π−Δ++Electroproduction Beam-Spin Asymmetries off the Proton” by S. Diehl et al. (CLAS Collaboration), published on 11 July 2023 in Physical Review Letters.
DOI: 10.1103/PhysRevLett.131.021901

Stefan Diehl, a native of Lich, Germany, engaged in physics studies to comprehend natural phenomena and the world’s essence. He has acquired bachelor’s, master’s, and doctoral degrees from JLU Giessen and is part of multiple collaborations like CLAS, PANDA, ePIC, and COMPASS, and has co-authored over 70 peer-reviewed papers.

The research project received funding from the U.S. Department of Energy.

Frequently Asked Questions (FAQs) about Proton Resonance

What is the main focus of the recent experiments at Jefferson Lab?

The primary aim of the recent experiments at Jefferson Lab is to investigate the three-dimensional structures of resonating protons and neutron resonances. This research contributes to the broader understanding of the early universe and the fundamental particles like nucleons, which are made up of quarks and gluons.

Who conducted the research and where was it published?

The research was led by a group of physicists from Justus Liebig Universitat (JLU) Giessen in Germany and the University of Connecticut. They spearheaded the CLAS Collaboration’s effort for this experiment. The findings have been recently published in the prestigious peer-reviewed journal Physical Review Letters.

What are nucleon resonances?

Nucleon resonances are the higher-energy states of nucleons (protons and neutrons), where the quarks inside the nucleons vibrate and rotate against each other. This phenomenon is essential for understanding the basic building blocks of matter.

What is the significance of understanding the 3D structure of a resonating proton?

A comprehensive understanding of the 3D structure of a resonating proton could provide valuable insights into the early universe and the fundamental particles that make up matter. It is crucial for advancing the field of particle physics and for a deeper understanding of cosmic origins.

What future research is planned in this area?

The team plans more experiments at Jefferson Lab using different targets and polarizations to probe various aspects of the scattering process. They also aim to study similar processes, such as the generation of resonance in combination with an energetic photon, to yield further crucial information.

What are the broader implications of this research for our understanding of the universe?

The research helps in deciphering the properties of the early cosmos shortly after the Big Bang. By understanding the characteristics of these resonances, scientists can glean insights into how matter was formed in the universe and why the universe exists in its current state.

Who funded the research study?

The research project received funding from the U.S. Department of Energy.

What novel contributions has this research made?

This study represents the first time a measurement or observation has been sensitive to the three-dimensional properties of nucleon resonances in an excited state, thus inaugurating a new domain of research in particle physics.

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