Toshimi Suda (Tohoku University): Proton Charge Radius

In 2010, a surprising discrepancy emerged between the proton charge radius measured using electrons and that measured using muons. Since the size of a particle is one of its most fundamental physical properties, this finding raised serious questions about our understanding of proton structure and triggered what is now known as the “proton radius puzzle.”

This puzzle has significant implications for particle, nuclear, and atomic physics, prompting intense experimental and theoretical efforts worldwide to resolve and understand the discrepancy and fix the radius value. Although several new high-precision measurements have been performed in recent years, the puzzle remains unsolved.

At Tohoku University, we have conducted electron-scattering experiments using the world’s lowest-energy electron beam, which provides a highly sensitive and model-independent method to determine the charge radius. Following five years of instrumental development, we completed two years of data collection in October 2024. The data are currently under analysis.

In this seminar, I will provide an overview of the proton radius puzzle, its scientific significance, and recent global progress, with a focus on our work at Tohoku University. If time allows, I will also introduce our efforts to measure the neutron charge radius.

Zoom Information:

https://us02web.zoom.us/j/2022111100

(Meeting code: 2022111100 Password: skcm2)