Shrinking the proton: Researchers confirm the small value of the proton radius determined from muonic hydrogen

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly smaller, by four standard deviations, ...

Proton-size puzzle deepens

Measurement in ordinary hydrogen agrees with a surprising 2010 result on the element's exotic cousin — but gives a smaller value than virtually every other experiment.

The proton radius revisited

Proton size still perplexes despite a new measurement

Study of hydrogen atoms supports the case for a smaller proton.

Shrinking the proton again

Scientists, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.