Dispersion relations for hadronic light-by-light scattering and the muon g – 2
The largest uncertainties in the Standard Model calculation of the anomalous magnetic moment of the muon (g – 2)μ come from hadronic effects, and in a few years the subleading hadronic light-by-light (HLbL) contribution might dominate the theory error. We present a dispersive description of the HLbL...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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EDP Sciences
2018-01-01
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| Series: | EPJ Web of Conferences |
| Online Access: | https://doi.org/10.1051/epjconf/201816600014 |
| _version_ | 1828918789893259264 |
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| author | Procura Massimiliano Colangelo Gilberto Hoferichter Martin Stoffer Peter |
| author_facet | Procura Massimiliano Colangelo Gilberto Hoferichter Martin Stoffer Peter |
| author_sort | Procura Massimiliano |
| collection | DOAJ |
| description | The largest uncertainties in the Standard Model calculation of the anomalous magnetic moment of the muon (g – 2)μ come from hadronic effects, and in a few years the subleading hadronic light-by-light (HLbL) contribution might dominate the theory error. We present a dispersive description of the HLbL tensor, which is based on unitarity, analyticity, crossing symmetry, and gauge invariance. This opens up the possibility of a data-driven determination of the HLbL contribution to (g – 2)μ with the aim of reducing model dependence and achieving a reliable error estimate.
Our dispersive approach defines unambiguously the pion-pole and the pion-box contribution to the HLbL tensor. Using Mandelstam double-spectral representation, we have proven that the pion-box contribution coincides exactly with the one-loop scalar-QED amplitude, multiplied by the appropriate pion vector form factors. Using dispersive fits to high-statistics data for the pion vector form factor, we obtain αμπ-box=−15.92×10−11. A first model-independent calculation of effects of ππ intermediate states that go beyond the scalar-QED pion loop is also presented. We combine our dispersive description of the HLbL tensor with a partial-wave expansion and demonstrate that the known scalar-QED result is recovered after partial-wave resummation. After constructing suitable input for the γ*γ* → ππ helicity partial waves based on a pion-pole left-hand cut (LHC), we find that for the dominant charged-pion contribution this representation is consistent with the two-loop chiral prediction and the COMPASS measurement for the pion polarizability. This allows us to reliably estimate S-wave rescattering effects to the full pion box and leads to αμπ-box+αμ,J=0ππ,π-pole LHC=−241×10−11. |
| first_indexed | 2024-12-13T21:15:33Z |
| format | Article |
| id | doaj.art-857fb0e67df44e1eba9072c135b84cdc |
| institution | Directory Open Access Journal |
| issn | 2100-014X |
| language | English |
| last_indexed | 2024-12-13T21:15:33Z |
| publishDate | 2018-01-01 |
| publisher | EDP Sciences |
| record_format | Article |
| series | EPJ Web of Conferences |
| spelling | doaj.art-857fb0e67df44e1eba9072c135b84cdc2022-12-21T23:31:14ZengEDP SciencesEPJ Web of Conferences2100-014X2018-01-011660001410.1051/epjconf/201816600014epjconf_kloe22018_00014Dispersion relations for hadronic light-by-light scattering and the muon g – 2Procura MassimilianoColangelo GilbertoHoferichter MartinStoffer PeterThe largest uncertainties in the Standard Model calculation of the anomalous magnetic moment of the muon (g – 2)μ come from hadronic effects, and in a few years the subleading hadronic light-by-light (HLbL) contribution might dominate the theory error. We present a dispersive description of the HLbL tensor, which is based on unitarity, analyticity, crossing symmetry, and gauge invariance. This opens up the possibility of a data-driven determination of the HLbL contribution to (g – 2)μ with the aim of reducing model dependence and achieving a reliable error estimate. Our dispersive approach defines unambiguously the pion-pole and the pion-box contribution to the HLbL tensor. Using Mandelstam double-spectral representation, we have proven that the pion-box contribution coincides exactly with the one-loop scalar-QED amplitude, multiplied by the appropriate pion vector form factors. Using dispersive fits to high-statistics data for the pion vector form factor, we obtain αμπ-box=−15.92×10−11. A first model-independent calculation of effects of ππ intermediate states that go beyond the scalar-QED pion loop is also presented. We combine our dispersive description of the HLbL tensor with a partial-wave expansion and demonstrate that the known scalar-QED result is recovered after partial-wave resummation. After constructing suitable input for the γ*γ* → ππ helicity partial waves based on a pion-pole left-hand cut (LHC), we find that for the dominant charged-pion contribution this representation is consistent with the two-loop chiral prediction and the COMPASS measurement for the pion polarizability. This allows us to reliably estimate S-wave rescattering effects to the full pion box and leads to αμπ-box+αμ,J=0ππ,π-pole LHC=−241×10−11.https://doi.org/10.1051/epjconf/201816600014 |
| spellingShingle | Procura Massimiliano Colangelo Gilberto Hoferichter Martin Stoffer Peter Dispersion relations for hadronic light-by-light scattering and the muon g – 2 EPJ Web of Conferences |
| title | Dispersion relations for hadronic light-by-light scattering and the muon g – 2 |
| title_full | Dispersion relations for hadronic light-by-light scattering and the muon g – 2 |
| title_fullStr | Dispersion relations for hadronic light-by-light scattering and the muon g – 2 |
| title_full_unstemmed | Dispersion relations for hadronic light-by-light scattering and the muon g – 2 |
| title_short | Dispersion relations for hadronic light-by-light scattering and the muon g – 2 |
| title_sort | dispersion relations for hadronic light by light scattering and the muon g 2 |
| url | https://doi.org/10.1051/epjconf/201816600014 |
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