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Taiwan physicists contribute to breakthrough of nuclear physics

2010/07/13 00:09

Taipei, July 13 (CNA) Recent experiments led by a group ofinternational researchers from 32 countries showed that the size of aproton is 4% smaller than what we long believed, said Yi-Wei Liu fromthe National Tsing Hua University (NTHU) Monday.

Liu, an associate professor with NTHU's Physics Department, isone of the main scientists contributed to develop the laser system toprobe the proton radius. Most of the experiments were carried out atthe Paul Scherrer Institute in Switzerland.

The trick used by Liu and his collaborators was substituting theelectron in a hydrogen atom with a muon. Muon is a radioactiveparticle whose mass is 207 times heavier than that of an electron.This implies that it can orbit at closer circumferences around theproton, providing a more sensitive probe to the proton radius.

After nearly 10 years of development effort, Liu and hiscollaborators concluded that the proton size is 0.84184 fm(femtometer), instead of currently recognized 0.8768 fm. A femtometeris equivalent to one- quadrillionth of a meter.

Liu said that the impact of this finding is rather significant since some theories for the atomic physics which have been prevalent for the last 100 years may need to be challenged. Thisincludes the quantum electrodynamics (QED) theories and the Ryberg constant, which is the most accurate physical constant measured todate.

As for direct applications to the daily lives of people, Liu saidhowever, may be still a far reached goal, but it calls for rewrittingthe content of the general physics textbook.

The physical reason behind this finding is presently unclear.Possible explanations include unknown interactions between theelectron/muon and the proton and higher order corrections to the QEDtheories.

The findings were published in the July 8th issue of Nature.

(By Bear Lee)