New data science techniques reveal precise measurement of proton’s tensor charge

Scientists have recently made a breakthrough in understanding the fundamental properties of protons. Protons are made up of smaller particles called quarks, which have an intrinsic property called spin. The spin of quarks can point in different directions, including in a direction perpendicular to the proton’s momentum, which is known as a transverse spin. In addition to electric charge, protons also have another fundamental charge called the tensor charge, which is the net transverse spin of quarks in a proton with transverse spin.

To obtain the tensor charge, scientists must use the theory of quantum chromodynamics (QCD) to extract the “transversity” function from experimental data. This function represents the difference between the number of quarks with their spin aligned and anti-aligned to the proton’s spin in a transverse direction. Using state-of-the-art data science techniques, researchers have recently made the most precise empirical determination of the tensor charge.

However, because of the phenomenon of confinement, quarks are always bound in protons or other hadrons. This presents a challenge in connecting QCD theory to experimental measurements of high-energy collisions involving hadrons.

To address this challenge, scientists from the TMD Collaboration and the JAM Collaboration analyzed data from various experiments where protons and/or quarks were transversely polarized. This allowed for the most precise empirical determination of the proton’s tensor charge to date, which is not only a fundamental property of the proton but also crucial in searches for new physics.

The results were compared to computations of the proton’s tensor charge by lattice QCD, which simulates the proton’s structure on a supercomputer. For the first time in about a decade of research, empirical methods and lattice QCD computations showed agreement for the proton’s tensor charge. These findings were published in Physical Review D.

The empirical study utilized QCD theory and state-of-the-art numerical methods, including data from electron-positron, electron-proton, and proton-proton scattering. This opens up a new frontier in QCD global analyses, where scientists can include all possible measurements, including those from the future Electron-Ion Collider and Jefferson Lab 12 GeV, to further increase the precision and accuracy of extracting the proton’s tensor charge.

Source: US Department of Energy

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