Stuttgart 2012 – wissenschaftliches Programm
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PV: Plenarvorträge
PV 10: PV X
PV 10.1: Preisträgervortrag
Mittwoch, 14. März 2012, 15:30–16:15, V53.01
The size of the proton from laser spectroscopy of an exotic hydrogen atom — •Randolf Pohl1,3 and Aldo Antognini2,3 — 1Max-Planck-Institut für Quantenoptik, Garching, Germany — 2ETH Zürich, Switzerland — 3Laureate of the Gustav-Hertz-Prize
The proton has a finite size because it is a composite system of quarks and gluons. The charge radius Rp of the proton has so far been known only with a low precision of about 1% from both electron scattering and precision spectroscopy of hydrogen.
We have recently determined Rp by means of laser spectroscopy of the exotic "muonic hydrogen" atom [1]. Here, the muon, which is the 200 times heavier cousin of the electron, orbits the proton with a 200 times smaller Bohr radius. This enhances the sensitivity of the muonic atom energy levels to the proton's finite size tremendously. Our new value Rp = 0.84184 (67) fm is ten times more precise than the generally accepted CODATA value, but it differs by 5 standard deviations from it.
A lively discussion about this discrepancy has started, considering bound-state QED, proton shape and structure, the value of the Rydberg constant and even new physics.
[1] R. Pohl, A. Antognini et al., Nature 466, 213 (2010)