Dispersive analysis for η→γγ ⋆

Hanhart, C.; Kupść, A.; Meißner, Ulf‐G.; Stollenwerk, F.; Wirzba, A.

doi:10.1140/epjc/s10052-013-2668-3

Cited by 119 publications

(161 citation statements)

References 61 publications

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“…A preliminary branching ratio Γ(η → e + e − γ)/Γ(η → γγ) was measured to be consistent with the BESIII measurement. However, the statistics of either BESIII or CLAS are not ample enough to determine, statistically, which theoretical model best represents the structure of the η meson [15][16][17]. Table 1 outlines the current measurements and theoretical predictions.…”

Section: Update On the Branching Ratio Measurement Of The η → E + E −mentioning

confidence: 99%

Light meson decays from photon-induced reactions with CLAS

Kunkel

2016

EPJ Web Conf.

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Abstract. Photoproduction experiments with the CEBAF Large Acceptance Spectrometer CLAS at the Thomas Jefferson National Facility produce data sets with competitive statistics of light mesons. With these data sets, measurements of transition form factors for η, ω, and η mesons via conversion decays can be performed using the invariant mass distribution of the final state dileptons. Tests of fundamental symmetries and information on the light quark mass difference can be performed using a Dalitz plot analysis of the meson decay. An overview of preliminary results, from existing CLAS data, and future prospects within the newly upgraded CLAS12 apparatus are given.

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Section: Update On the Branching Ratio Measurement Of The η → E + E −mentioning

confidence: 99%

Light meson decays from photon-induced reactions with CLAS

Kunkel

2016

EPJ Web Conf.

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“…In this framework, we worked out how to define unambiguously and in a model-independent way both the pion-pole and the pion-box contribution. 1 With pion-as well as η-, η -pole contributions determined by their doubly-virtual transition form factors, which by themselves are strongly constrained by unitarity, analyticity, and perturbative QCD in combination with experimental data [38][39][40][41][42][43][44][45][46], we here apply our framework to extend the partial-wave formulation of two-pion rescattering effects for S-waves [28] to arbitrary partial waves. To this end, we identify a special set of (unambiguously defined) scalar functions that fulfill unsubtracted dispersion relations and can be expressed as linear combinations of helicity amplitudes.…”

Section: Introductionmentioning

confidence: 99%

Dispersion relation for hadronic light-by-light scattering: two-pion contributions

Colangelo

Hoferichter

Procura

et al. 2017

J. High Energ. Phys.

385

257

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In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon (g − 2) µ , including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of γ * γ * → ππ. We validate the formalism extensively using the pion-box contribution, defined by two-pion intermediate states with a pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the pion vector form factor, we provide an evaluation of the full pion box, a π-box µ = −15.9(2)×10 −11 . As an application of the partial-wave formalism, we present a first calculation of ππ-rescattering effects in HLbL scattering, with γ * γ * → ππ helicity partial waves constructed dispersively using ππ phase shifts derived from the inverse-amplitude method. In this way, the isospin-0 part of our calculation can be interpreted as the contribution of the f 0 (500) to HLbL scattering in (g − 2) µ . We argue that the contribution due to charged-pion rescattering implements corrections related to the corresponding pion polarizability and show that these are moderate. Our final result for the sum of pion-box contribution and its S-wave rescattering corrections reads a π-box µ + a ππ,π-pole LHC µ,J=0 = −24(1) × 10 −11 .

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“…Theoretical calculations are in (a) from Terschlüsen and Leupold (TL) [33] (dashed-dotted line) and the model independent method based on Padé-approximants [38] (dashed line with error band). In (b) a calculation based on dispersion theory (DT) is shown [39] (dotted line with error band).…”

Section: Preliminary Results For η → π 0 γγmentioning

confidence: 99%

ηandη′Physics at MAMI

Unverzagt

2014

EPJ Web of Conferences

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Abstract. The Crystal Ball/TAPS setup at MAMI is ideally suited to detect neutral and electromagnetic decays of the η and η mesons. In this contribution recent results on η and η decays from the Crystal Ball/TAPS experiment at MAMI are presented. These are the accurate measruement of η photoproduction cross-sections in the threshold region, the determination of the timelike electromagnetic transition form factors, and a test of low-energy QCD with the η → π 0 γγ decay. Finally, further perspectives are discussed.

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Dispersive analysis for η→γγ ⋆

Abstract: A dispersion integral is derived that connects data on η → π + π − γ to the η → γγ * transition form factor. A detailed analysis of the uncertainties is provided. We find for the slope of the η transition form factor at the origin b η = 2.05

Cited by 119 publications

References 61 publications

Light meson decays from photon-induced reactions with CLAS

Light meson decays from photon-induced reactions with CLAS

Dispersion relation for hadronic light-by-light scattering: two-pion contributions

ηandη′Physics at MAMI

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