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Existence of nuclear modifications of the nucleon longitudinal-transverse structure-function ratio

S. Kumano

  • Quark Matter Research Center, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; Southern Center for Nuclear Science Theory, Institute of Modern Physics, Chinese Academy of Sciences, Huizhou 516000, China; Department of Mathematics, Physics, and Computer Science, Faculty of Science, Japan Women's University, Mejirodai 2-8-1, Tokyo 112-8681, Japan; and KEK Theory Center, Institute of Particle and Nuclear Studies, KEK, Oho 1-1, Tsukuba 305-0801, Japan

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Phys. Rev. C 113, 015206 – Published 26 January, 2026

DOI: https://doi.org/10.1103/xgbh-grqx

Abstract

It has been assumed that nuclear modification does not exist in the longitudinal-transverse structure-function ratio RN=FLN/(2xF1N) in lepton deep inelastic scattering. This assumption is widely used in obtaining structure functions of the “nucleon” from nuclear data such as the deuteron ones. However, nuclear modifications do exist theoretically at least in medium- and large-x regions because nucleons in a nucleus move in any direction, which is not necessarily the longitudinal direction of the virtual-photon or weak-boson momentum in lepton scattering. Because of this transverse motion, the nucleon's transverse and longitudinal structure functions should mix with each other in nuclei with the mixture probability proportional to the nucleon's transverse momentum squared p⃗T2/Q2. In this work, numerical results are explicitly shown regarding such nuclear modifications in the deuteron. These nuclear modifications are important for determining precise structure functions of the nucleon. Furthermore, modifications of RN should be investigated also at small x by the future electron-ion collider to find interesting gluon dynamics in nuclei. Hopefully, this nuclear effect of RN could be found by future experimental measurements at lepton accelerator facilities.

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Phys. Rev. C 113, 015206– Published 26 January, 2026
  • Received 23 June 2025
  • Revised 3 November 2025
  • Accepted 20 November 2025
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