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Hyperfine splittings in muonic atoms and laser technology

Objective

The proton radius extracted from the measurements of the 2S-2P energy splitting in muonic hydrogen
(μp) has attracted great attention because of a 7σ discrepancy with the values extracted from
electron scattering and hydrogen (H) spectroscopy. Hundreds of publications have been devoted to the
so called “proton radius puzzle” ranging from studies of physics beyond the standard model, to reanalysis
of electron scattering data, refinements of bound-state QED calculations, new theories describing
the proton structure, and proposals for new scattering and H spectroscopy experiments.
As next step, I plan two new (i.e. never before attempted) measurements: the ground-state hyperfine
splitting (1S-HFS) in both μp and μ3He+ with 1 ppm relative accuracy by means of pulsed laser
spectroscopy. From these measurements the nuclear-structure contributions (two-photon-exchange)
can be extracted with a relative accuracy of 100 ppm which in turn can be used to extract the corresponding
Zemach radii (with a relative accuracy of 0.1%) and polarizability contributions. The Zemach radii
can provide magnetic radii when form-factor data or models are assumed.
These radii are benchmarks for lattice QCD and few-nucleon theories. With the polarizability contribution
they impact our models of the proton and of the 3He nucleus. Moreover, the μp measurement
can be used to solve the discrepancy between the magnetic radii values as extracted from polarized and
unpolarized electron scattering and to further test bound-state QED predictions of the 1S-HFS in H.
These two experiments require a muon beam line, a target with an optical cavity, detector, and laser
systems. As weak M1 transitions must be probed, large laser-pulse energies are needed, thus cutting-edge
laser technologies (mainly thin-disk laser and parametric down-conversion) need to be developed.
Laser schemes of potentially high industrial impact that I have just patented will be implemented and
refined.

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Programme(s)

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Topic(s)

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Funding Scheme

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ERC-COG - Consolidator Grant

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Call for proposal

Procedure for inviting applicants to submit project proposals, with the aim of receiving EU funding.

(opens in new window) ERC-2016-COG

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Host institution

PAUL SCHERRER INSTITUT
Net EU contribution

Net EU financial contribution. The sum of money that the participant receives, deducted by the EU contribution to its linked third party. It considers the distribution of the EU financial contribution between direct beneficiaries of the project and other types of participants, like third-party participants.

€ 1 378 994,75
Address
FORSCHUNGSTRASSE 111
5232 VILLIGEN PSI
Switzerland

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Region
Schweiz/Suisse/Svizzera Nordwestschweiz Aargau
Activity type
Research Organisations
Links
Total cost

The total costs incurred by this organisation to participate in the project, including direct and indirect costs. This amount is a subset of the overall project budget.

€ 1 378 994,75

Beneficiaries (2)

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