Abstract
Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring the application of non-perturbative techniques such as chiral effective field theory1. Here we present measurements of the neutron’s generalized spin polarizabilities that quantify the neutron’s spin precession under electromagnetic fields at very low energy-momentum transfer squared down to 0.035 GeV2. In this regime, chiral effective field theory calculations2,3,4 are expected to be applicable. Our data, however, show a strong discrepancy with these predictions, presenting a challenge to the current description of the neutron’s spin properties.
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Data availability
All experimental data that support the findings of this study are provided in the Supplementary Information or are available from J.P.C. (jpchen@jlab.org), A.D. (deurpam@jlab.org), C.P. (cpeng@jlab.org) or V.S. (vasulk@jlab.org) upon request.
Code availability
The computer codes that support the plots within this paper and the findings of this study are available from J.P.C. (jpchen@jlab.org), A.D. (deurpam@jlab.org), C.P. (cpeng@jlab.org) or V.S. (vasulk@jlab.org) upon request.
Change history
03 March 2022
A Correction to this paper has been published: https://doi.org/10.1038/s41567-022-01569-0
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Acknowledgements
All authors are members of The Jefferson Lab E97-110 Collaboration. We acknowledge the outstanding support of the Jefferson Lab Hall A technical staff and the Physics and Accelerator Divisions that made this work possible. We thank A. Deltuva, J. Golak, F. Hagelstein, H. Krebs, V. Lensky, U.-G. Meißner, V. Pascalutsa, G. Salmè, S. Scopetta and M. Vanderhaeghen for useful discussions and for sharing their calculations. We are grateful to V. Pascalutsa and M. Vanderhaeghen for suggesting a comparison of the data to the Schwinger relation. This material is based upon work supported by the United States Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 and by the United States National Science Foundation under grant PHY-0099557.
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The members of the Jefferson Lab E97-110 Collaboration constructed and operated the experimental equipment used in this experiment. All authors contributed to the data collection, experiment design and commissioning, data processing, data analysis or Monte Carlo simulations. The following authors especially contributed to the main data analysis: J.P.C., A.D., C.P. and V.S.
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Supplementary Information
Supplementary Tables 1–4.
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Sulkosky, V., Peng, C., Chen, Jp. et al. Measurement of the generalized spin polarizabilities of the neutron in the low-Q2 region. Nat. Phys. 17, 687–692 (2021). https://doi.org/10.1038/s41567-021-01245-9
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DOI: https://doi.org/10.1038/s41567-021-01245-9
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