Beam-Normal Single-Spin Asymmetry in $^{208}$Pb at low energy: discrepancy resolved or new kinematic puzzle?
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arXiv
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| Autori principali: | , , , , , , , , , , , , , , , , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| author | Esser, A. Kozyrev, N. Aulenbacher, K. Baunack, S. Dehn, M. Del Vincio, A. Doria, L. Hoek, M. Keil, F. Maas, F. Merkel, H. Mihovilovic, M. Müller, U. Pochodzalla, J. Schlimme, B. S. Shao, T. Stengel, S. Thiel, M. Wilhelm, L. Sfienti, C. |
| author_facet | Esser, A. Kozyrev, N. Aulenbacher, K. Baunack, S. Dehn, M. Del Vincio, A. Doria, L. Hoek, M. Keil, F. Maas, F. Merkel, H. Mihovilovic, M. Müller, U. Pochodzalla, J. Schlimme, B. S. Shao, T. Stengel, S. Thiel, M. Wilhelm, L. Sfienti, C. |
| contents | A longstanding discrepancy between measured and predicted beam-normal single-spin asymmetries $A_{n}$ in elastic electron scattering off $^{208}$Pb has challenged our understanding of two-photon exchange (TPE) in heavy nuclei. We report a new measurement at 570 MeV and $Q^2$=0.04 $GeV^2$/$c^2$, yielding$A_n = (-9.1 \pm 2.1~\text{(stat)} \pm 0.7~\text{(syst)})~\mathrm{ppm}$. This nonzero value contrasts with previous results at higher energies and suggests a kinematic dependence of TPE effects not captured by current theory, prompting a reevaluation of earlier interpretations. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_18851 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Beam-Normal Single-Spin Asymmetry in $^{208}$Pb at low energy: discrepancy resolved or new kinematic puzzle? Esser, A. Kozyrev, N. Aulenbacher, K. Baunack, S. Dehn, M. Del Vincio, A. Doria, L. Hoek, M. Keil, F. Maas, F. Merkel, H. Mihovilovic, M. Müller, U. Pochodzalla, J. Schlimme, B. S. Shao, T. Stengel, S. Thiel, M. Wilhelm, L. Sfienti, C. Nuclear Experiment High Energy Physics - Experiment Nuclear Theory A longstanding discrepancy between measured and predicted beam-normal single-spin asymmetries $A_{n}$ in elastic electron scattering off $^{208}$Pb has challenged our understanding of two-photon exchange (TPE) in heavy nuclei. We report a new measurement at 570 MeV and $Q^2$=0.04 $GeV^2$/$c^2$, yielding$A_n = (-9.1 \pm 2.1~\text{(stat)} \pm 0.7~\text{(syst)})~\mathrm{ppm}$. This nonzero value contrasts with previous results at higher energies and suggests a kinematic dependence of TPE effects not captured by current theory, prompting a reevaluation of earlier interpretations. |
| title | Beam-Normal Single-Spin Asymmetry in $^{208}$Pb at low energy: discrepancy resolved or new kinematic puzzle? |
| topic | Nuclear Experiment High Energy Physics - Experiment Nuclear Theory |
| url | https://arxiv.org/abs/2508.18851 |