Eric A. Hessels is a

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate caus ...

, currently a

Canada Research Chair Canada Research Chair (CRC) is a title given to certain Canadian university research professors by the Canada Research Chairs Program. Program goals The Canada Research Chair program was established in 2000 as a part of the Government of Canada ...

and Distinguished

Research Professor Professor (commonly abbreviated as Prof.) is an academic rank at universities and other post-secondary education and research institutions in most countries. Literally, ''professor'' derives from Latin as a "person who professes". Professors ...

York University York University (french: Université York), also known as YorkU or simply YU, is a public university, public research university in Toronto, Ontario, Canada. It is Canada's fourth-largest university, and it has approximately 55,700 students, 7,0 ...

in Toronto, Ontario. In September 2019, Hessels et al. measured the

Lamb shift In physics, the Lamb shift, named after Willis Lamb, is a difference in energy between two energy levels 2''S''1/2 and 2''P''1/2 (in term symbol notation) of the hydrogen atom which was not predicted by the Dirac equation, according to which the ...

for

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

to measure the radius of a

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

and demonstrated that it is consistent with the value obtained for

muonic hydrogen An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example, electrons may be replaced by other negatively charged particles such as muons (muonic atoms) ...

. This proved that the supposed discrepancy known as the

proton radius puzzle The proton radius puzzle is an unanswered problem in physics relating to the size of the proton. Historically the proton charge radius was measured by two independent methods, which converged to a value of about 0.877 femtometres (1 fm = 10−15 m ...

did not exist.

References

Year of birth missing (living people) Living people Academic staff of York University Canadian physicists 21st-century Canadian astronomers University of Notre Dame alumni Canada Research Chairs {{physicist-stub