The positronium hyperfine structure: Progress towards a direct measurement of the 23S1 → 21S0 transition in vacuum

Heiss, M. W.; Wichmann, Gunther; Rubbia, A.

doi:10.1088/1742-6596/1138/1/012007

Cited by 16 publications

(12 citation statements)

References 26 publications

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“…The effects are thus numerically smaller than the mα 7 effects currently under study [45][46][47][48][49][50][51][52][53][54][55][56][57].…”

Section: E Positroniummentioning

confidence: 84%

“…Coupling parameters for the muon have been estimated in Eqs. (43) and (45) for the vector and pseudoscalar models, respectively. A quick calculation shows that the relative correction to the hyperfine splitting, for S states, remains the same for the system of particle and antiparticle, despite the existence of the annihilation channel, provided the reduced mass of the system in properly taken into account.…”

Section: Muonic Hydrogenmentioning

confidence: 99%

“…Quite considerable efforts have recently been invested in the calculation of the mα 7 corrections to the positronium hyperfine splitting, [45][46][47][48][49][50][51][52][53][54][55][56][57]. In positronium, effects of the X17 particle are suppressed in view of the smaller reduced mass of the bound system.…”

Section: E Positroniummentioning

confidence: 99%

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Fifth Force and Hyperfine Splitting in Bound Systems

Jentschura

2020

Preprint

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Two recent experimental observations at the ATOMKI Institute of the Hungarian Academy of Sciences (regarding the angular emission pattern of electron-positron pairs from nuclear transitions from excited states in 8 Be and 4 He) indicate the possible existence of a particle of a rest mass energy of roughly 17 MeV. The so-called X17 particle constitutes a virtual state in the process, preceding the emission of the electron-positron pair. Based on the symmetry of the nuclear transitions (1 + → 0 + and 0 − → 0 + ), the X17 could either be a vector, or a pseudoscalar particle. Here, we calculate the effective potentials generated by the X17, for hyperfine interactions in simple atomic systems, for both the pseudoscalar as well as the vector X17 hypotheses. The effective Hamiltonians are obtained in a general form which is applicable to both electronic as well as muonic bound systems. Because of the short range of the X17-generated potentials, the most promising pathway for the observation of the X17-mediated effects in bound systems concerns hyperfine interactions, which, for S states, are given by modifications of short-range (Dirac-δ) potentials in coordinate space. For the pseudoscalar hypothesis, the exchange of one virtual X17 quantum between the bound lepton and the nucleus exclusively leads to hyperfine effects, but does not affect the Lamb shift. Effects due to the X17 are shown to be drastically enhanced for muonic bound systems. Prospects for the detection of hyperfine effects mediated by X17 exchange are analyzed for muonic deuterium, muonic hydrogen, true muonium (µ + µ − bound system), and positronium. I. INTRODUCTIONFor decades, atomic physicists have tried to push the accuracy of experiments and theoretical predictions of transitions in simple atomic systems higher [1]. The accurate measurements have led to stringent limits on the time variation of fundamental constants [2-4], and enabled us to determine a number of important fundamental physical constants [5] with unprecedented accuracy. Yet, a third motivation, hitherto not crowned with success, has been the quest to find signs of a possible low-energy extension of the Standard Model, based on a deviation of experimental results and theoretical predictions.Recently, the possible existence of a fifth-force particle, commonly referred to as the "X17" particle because of the observed rest mass of 16.7 MeV, has been investigated in Refs. [6,7], based on a peak in the emission spectrum of electron-positron pairs in nuclear transitions of excited helium and beryllium nuclei. Two conceivable theoretical explanations have been put forward, both being based on low-energy additions to the Standard Model. The first of these involves a vector particle (a "massive, dark photon", see Refs. [8,9]), and the second offers a pseudoscalar particle (see Ref. [10]), which couples to light fermions as well as hadrons.Somewhat unfortunately, the rest mass range of 16.7 MeV makes the X17 particle hard to detect in atomic physics experiments. The observed X17 rest mass energy...

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“…The effects are thus numerically smaller than the mα 7 effects currently under study [45][46][47][48][49][50][51][52][53][54][55][56][57].…”

Section: E Positroniummentioning

confidence: 84%

Section: Muonic Hydrogenmentioning

confidence: 99%

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Fifth Force and Hyperfine Splitting in Bound Systems

Jentschura

2020

Preprint

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“…Having in mind various projects on accurate measurements of pure leptonic properties, such as the anomalous magnetic moment of electron [68] and muon [67,69], energy intervals in muonium [70,71] and positronium [72,73], progress in related theoretical QED calculations [74][75][76][77][78], and in determination of involved fundamental constants (such as the fine structure constant α [79]), a better understanding of related hVP contributions, that is one of the limiting factor of theory of pure leptonic systems, is important.…”

Section: Discussionmentioning

confidence: 99%

Hadronic vacuum-polarization contribution to various QED observables

Karshenboim

Shelyuto

2021

Eur. Phys. J. D

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Due to precision tests of quantum electrodynamics (QED), determination of accurate values of fundamental constants, and constraints on new physics, it is important in a consistent way to evaluate a number of QED observables such as the Lamb shift in hydrogen-like atomic systems. Even in a pure leptonic case, those QED variables are in fact not pure QED ones since hadronic effects are involved through intermediate states while accounting for higher-order effects. One of them is hadronic vacuum polarization (hVP). Complex evaluations often involve a number of QED quantities, for which treatment of hVP is not consistent. The highest accuracy for a calculation of the hVP term is required for the anomalous magnetic moment of a muon. However, a standard data-driven treatment of hVP, based on a dispersion integration of experimental data on electron-positron annihilation to hadrons and some other phenomena, leads to a contradiction with the experimental value of $$a_\mu $$ a μ . This experimental value can be considered as an indirect determination of the hVP contribution to $$a_\mu $$ a μ and the scatter of theory and experiment allows one to obtain a conservative estimation of the related hVP contribution. In this paper, we derive exact and approximate relations between the leading-order (LO) hVP contributions to various observables. Using those relations, we obtain for them a consistent set of the results, based on the scatter of $$a_\mu $$ a μ values. While calculating the LO hVP term, we have to remember that next-to-LO (NLO) hVP corrections are often comparable with the uncertainty of the LO term. Special attention is payed to hVP contribution to simple atoms. In particular, we discuss the NLO contribution to the Lamb shift in ordinary and muonic hydrogen and other two-body atoms for $$Z\le 10$$ Z ≤ 10 . We also consider the NLO contribution of the muonic vacuum polarization to the Lamb shift in hydrogen-like atoms. With the $$a_\mu $$ a μ puzzle unresolved, one may still require present-days values of the hVP contributions to various observable for comparison to experiment etc. the presence of contradicting values and a lack of consistency means an additional uncertainty for $$a_\mu $$ a μ and for key contributions to it, including the LO hVP one. We present here an estimation of such a propagated uncertainty in hVP contributions to different QED observables and recommend a consistent set of the related LO hVP contributions. Graphic Abstract

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“…Ps spectroscopy is an active field with current efforts focused on measuring optical and microwave transitions from its ground [4] and first-excited states [5,6]. The recent measurement of the Ps n = 2 fine-structure is 4.5 standard deviations from its calculated value [6],…”

Section: Introductionmentioning

confidence: 99%

Current status and prospects of muonium spectroscopy at PSI

Ohayon

Burkley

2021

SciPost Phys. Proc.

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Recent and ongoing developments of low energy muon beamlines are heralding a new era of precision Muonium spectroscopy. While past spectroscopic measurements of Muonium were performed at pulsed muon facilities and were statistically limited, the advent of continuous low energy muon beams, such as at the LEM beamline at PSI, paired with the development of efficient muon-muonium converters and laser advancements, will overcome these limitations. Current experiments presently underway at the LEM facility and in the near future at the muCool beamline, which is under development at PSI, aim to improve the precision of both the 1S-2S transition determination and Lamb shift by several orders of magnitude. In this Chapter we give an overview of the current status and future prospects of these activities at PSI, highlighting how their projected significance fits into a broader context of other ongoing efforts worldwide.

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The positronium hyperfine structure: Progress towards a direct measurement of the 2³S₁ → 2¹S₀ transition in vacuum

Cited by 16 publications

References 26 publications

Fifth Force and Hyperfine Splitting in Bound Systems

Fifth Force and Hyperfine Splitting in Bound Systems

Hadronic vacuum-polarization contribution to various QED observables

Current status and prospects of muonium spectroscopy at PSI

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