Abstract
Understanding the spin structure of hadrons in the small x regime is an important direction to unravel the spin puzzle in hadronic physics. To include spin degrees of freedom in the small x regime requires going beyond the usual eikonal approximation in high energy QCD. We developed an effective Hamiltonian approach to study spin related observables in the small x regime using the shockwave formalism. The small-x effective Hamiltonian incorporates both quark and gluon propagators in the background fields and the background field induced interaction vertices up to next-to-eikonal order. A novel feature of sub-eikonal interactions is the background gluon field induced gluon radiation inside the shockwave. Its relation to chromo-electrically polarized Wilson line correlator is established both in small x helicity evolution and in longitudinal double-spin asymmetry for gluon production.
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Acknowledgments
I thank Yuri Kovchegov for very helpful and inspiring discussions. I am grateful to Daniel Adamiak for discussions and checking many equations in the paper. I also appreciate very interesting conversations with Florian Cougoulic and Guillaume Beuf on related topics. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Award Number DE-SC0004286.
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Li, M. Small x physics beyond eikonal approximation: an effective Hamiltonian approach. J. High Energ. Phys. 2023, 158 (2023). https://doi.org/10.1007/JHEP07(2023)158
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DOI: https://doi.org/10.1007/JHEP07(2023)158