Precision measurments of quantum transitions in exotic atoms

Project Information

QUARTET

Grant agreement ID: 101019414

DOI

10.3030/101019414

Project terminated on 1 March 2023

EC signature date 19 March 2021

Start date 1 April 2021

End date 31 March 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 203 149,44

EU contribution

€ 203 149,44

Coordinated by

EIDGENOESSISCHE TECHNISCHE HOCHSCHULE ZUERICH
Switzerland

Periodic Reporting for period 1 - QUARTET (Precision measurments of quantum transitions in exotic atoms)

Reporting period: 2021-04-01 to 2023-03-31

Summary of the context and overall objectives of the project

Based on our understanding of the universe, we, who are made of matter, should not exist. This is due to the fact that the subatomic world is largely indifferent between matter and antimatter, predicting that they would be created in almost equal amounts in a big-bang scenario, and subsequently annihilate to form pure energy. This conundrum is called the baryon asymmetry problem. It is one of the major and most pressing unsolved questions in science today. One way of addressing this issue is to look for deviations between precision measurements and Standard Model predictions. However, a major limitation arises in the stage of comparison with theory due to nuclear-structure effects. Conducting measurements with exotic atoms overcomes this limitation, either by comparing measured properties between atoms and anti-atoms directly with no input from theory, or by measuring systems composed of particles with no internal structure. QUARTET—Quantum transitions in exotic atoms, will pursue both directions through two complementary experimental campaigns:

1. Muonium spectroscopy using the most intense low-energy muon beam at PSI.
2. Antihydrogen spectroscopy using the most intense low-energy proton beam at the ELENA beamline at CERN.

QUARTET will focus on transitions in the microwave region of the electromagnetic spectrum, namely the classical Lamb Shift, which for Antihydrogen has an added value: If no difference between matter and its counterpart is observed, this measurement will provide the first determination of the antiproton charge radius.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main research and development performed in this work were the design optimization and implementation of microwave spectroscopy setups for muonium and antihydrogen. The entire system (tagging, spectroscopy, detection) has been successfully commissioned with protons using the local
proton beam at the LEM beamline at PSI. This work helped to identify and solve several problems before the online data-taking. Namely, a crosstalk between the two photon-detectors which was solved by biasing the field between them to break the symmetry and have all electrons collected on one detector, which effectively decommissioned it. Following the commissioning phase we conducted a successful experiment, where we measured and published the lamb shift in muonium to within 2 MHz, an order of magnitude of improvement upon the best previous measurement. The factor 2 larger uncertainty from the goal uncertainty of 1 MHz was due mostly from having to decommission one of the photon detectors. A second experiment followed, and was published, where we investigated means of reducing lineshape (systematic) uncertainties via a different scanning strategy. This work was done as planned within the Mu-MASS collaboration, which was beneficial for both this work and the main Mu-MASS experiment.

Following the success of the design and commissioning of the microwave spectroscopy setup with muonium, I have adapted the setup to fit the GBAR beamline at CERN. We successfully implemented another setup there, considering the more stringent constraints on vacuum level and beam transmission. To commission the setup, we used a local pulsed proton beam.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Within the scope of QUARTET, we measured the lamb shift in muonium an order of magnitude better than the state of the art, and made significant advances towards performing a similar measurement with antihydrogen. The main motivation for such measurement is rooted in fundamental physics. We would like to shed light on two pressing and timely scientific issues. First, whether the muon is “just” a heavy electron. Second, whether the antiproton has exactly the same structure as the proton.

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