Abstract
The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high-energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly energetic real photon is emitted from one of the quarks inside the nucleon, which carries information on the quark’s transverse position and longitudinal momentum. By measuring the cross-section of deeply virtual Compton scattering, Compton form factors related to the generalized parton distributions can be extracted. Here, we report the observation of unpolarized deeply virtual Compton scattering off a deuterium target. From the measured photon-electroproduction cross-sections, we have extracted the cross-section of a quasifree neutron and a coherent deuteron. Due to the approximate isospin symmetry of quantum chromodynamics, we can determine the contributions from the different quark flavours to the helicity-conserved Compton form factors by combining our measurements with previous ones probing the proton’s internal structure. These results advance our understanding of the description of the nucleon structure, which is important to solve the proton spin puzzle.
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Data availability
Data that support the findings of this study are publicly available at https://userweb.jlab.org/~mazouz/NP/.
Code availability
The computer codes that support the plots within this paper and the findings of this study are available from M. Mazouz on request.
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Acknowledgements
We acknowledge the essential work of the Jefferson Lab accelerator staff and the Hall A technical staff. This work was supported by the Department of Energy (DOE), the National Science Foundation, the French Centre National de la Recherche Scientifique, the Agence Nationale de la Recherche, the Commissariat à l’énergie atomique et aux énergies alternatives and P2IO Laboratory of Excellence. Jefferson Science Associates, LLC, operates Jefferson Lab for the US DOE under US DOE contract DE-AC05-060R23177.
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The Jefferson Lab Hall A Collaboration constructed and operated the experimental equipment used in this experiment. Data were taken by a large number of collaboration members. The authors who performed data analyses and Monte Carlo simulations were M. Benali, C.D., M. Mazouz and C.M.C. The main authors of this manuscript were M. Benali, M. Mazouz, C.M.C., C.H., J.R. and A.C. It was reviewed by the entire collaboration before publication, and all authors approved the final version of the manuscript.
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Extended data
Extended Data Fig. 1 Fit results on the 2010 data of E07-007 and E08-025 experiments.
The plots show the helicity-independent (black) and helicity-dependent (blue) photon electroproduction cross-sections off proton (circles) and neutron (squares) from17 and the data reported herein. The error bars correspond to the quadratic sum of the standard deviation statistical and systematic uncertainties on the cross-sections. The specific kinematics are indicated in each plot. Solid lines show the results of the HT fit described in this work, whereas the dashed lines (almost indistinguishable from the solid lines) show the results of the NLO fit.
Extended Data Fig. 2 Fit results on the 2004 data of E00-110 and E03-106 experiments.
The plots show the helicity-independent (black) and helicity-dependent (blue) photon electroproduction cross-sections off proton (points) and neutron (squares) from12,26. The specific kinematics are indicated in each plot. Solid lines show the results of the HT fit described in this work, whereas the dashed lines (almost indistinguishable from the solid lines) show the results of the NLO fit. Neutron results in26 only contain the amplitude of the DVCS-BH interference term and its standard deviation uncertainty. Data points in this figure for that experiment are placed along the calculated cross-section, but without any spread around it.
Source data
Source Data Fig. 3
Table containing the data of Fig. 3f.
Source Data Fig. 4
Table containing the data of Fig. 4f.
Source Data Fig. 5
Table containing the data of Fig. 5f.
Source Data Fig. 6
Table containing the data of Fig. 6f.
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Benali, M., Desnault, C., Mazouz, M. et al. Deeply virtual Compton scattering off the neutron. Nat. Phys. 16, 191–198 (2020). https://doi.org/10.1038/s41567-019-0774-3
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DOI: https://doi.org/10.1038/s41567-019-0774-3
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