https://doi.org/10.1140/epjc/s10052-020-7678-3
Regular Article - Theoretical Physics
D-wave effects in diffractive electroproduction of heavy quarkonia from the photon-like 
transition
1
Departamento de Física, Universidad Técnica Federico Santa María, Casilla 110-V, Valparaiso, Chile
2
Czech Technical University in Prague, FNSPE, Břehová 7, 11519, Prague, Czech Republic
3
Institute of Experimental Physics SAS, Watsonova 47, 04001, Kosice, Slovakia
4
Department of Astronomy and Theoretical Physics, Lund University, 223 62, Lund, Sweden
5
Nuclear Physics Institute ASCR, 25068, Řež, Czech Republic
6
Departamento de Física, CFM, Universidade Federal de Santa Catarina, C.P. 476, Florianópolis, SC, CEP 88.040-900, Brazil
* e-mail: nemcik@saske.sk
Received:
3
October
2019
Accepted:
25
January
2020
Published online:
5
February
2020
We analyse the validity of a commonly used identification between structures of the virtual photon 
and vector meson transitions. In the existing studies of S-wave vector-meson photoproduction in the literature, such an identification is typically performed in the light-front (LF) frame while the radial component of the meson wave function is rather postulated than computed from the first principles. The massive photon-like vertex, besides the S-wave component, also contains an extra D-wave admixture in the 
rest frame. However, the relative weight of these contributions cannot be justified by any reasonable nonrelativistic potential model. In this work, we investigate the relative role of the D-wave contribution starting from the photon-like quarkonium transition in both frames: in the rest frame (with subsequent Melosh spin transform to the LF frame) and in the LF frame (without Melosh transform). In both cases, we employ the same radial wave functions found in the potential approach. We show that the photon-like transition imposed in the rest frame, with subsequent boosting to the LF frame, leads to significant discrepancies with the experimental data. In the second case, i.e. imposing the photon-like transition straight in the LF frame, we find that the corresponding total 
photoproduction cross sections are very close to those obtained with the “S-wave only” transition, both leading to a good description of the data. However, we find that the “S-wave only” transition leads to a better description of photoproduction data for excited (e.g. 
) heavy quarkonium states, which represent a more effective tool for study of D-wave effects. Consequently, the predictions for production of excited states based on the photon-like structure of transition should be treated with a great care due to a much stronger sensitivity of the D-wave contribution to the nodal structure of quarkonium wave functions.
© The Author(s), 2020
