Thu, Mar 07, 2013 - Page 3 News List

Size of proton may be smaller than thought: research

By Lee I-chia  /  Staff reporter

An international research team including scientists from National Tsinghua University yesterday said that protons may be smaller than previously assumed.

Liu Yi-wei (劉怡維), a founding member of the team and an associate professor at the university’s physics department, said that mainly hydrogen spectroscopy and electron scattering are used to measure the size of a proton.

However, using a new technique in which a muon (a heavy, unstable, relative of the proton) is placed in orbit around a proton, producing an atom called muonic hydrogen, the team found the radius of a proton to measure 0.84087 femtometers, Liu said.

The new measurement is approximately 4 percent smaller than the widely accepted radius of 0.8768 femtometers that is recognized by the Committee on Data for Science and Technology.

A femtometer is a billionth of a billionth of a meter, or a billionth of nanometer, said Gwo Shangjr (果尚志), a professor at the university’s physics department and head of the research and development office.

The precision of the new measurement was increased by 1.7 times, Gwo said, adding that the small, but significant difference in the measurements presents a perplexing puzzle to scientists around the world.

The results of the experiment show that there are still missing pieces in scientists’ understanding of quantum electrodynamics, Liu said.

A new international research team consisting of scientists from nine countries has been formed to continue solving the “proton size puzzle” with experiments on muonic helium, he added.

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