We calculate the transition form factor between vector and pseudoscalar quarkonia in both the timelike and the spacelike region using light-front dynamics. We investigate the frame dependence of the form factors for heavy quarkonia with light-front wave functions calculated from the valence Fock sector. This dependence could serve as a measure for the Lorentz symmetry violation arising from the Fock-space truncation. We suggest using frames with minimal longitudinal momentum transfer for calculations in the valence Fock sector, namely, the Drell-Yan frame for the spacelike region and a specific longitudinal frame for the timelike region; at q2=0 these two frames give the same result. We also use the transition form factor in the timelike region to investigate the electromagnetic Dalitz decay ψA→ψBl+l- (l=e, μ) and predict the effective mass spectrum of the lepton pair.
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We wish to thank Shaoyang Jia, Tobias Frederico, Shuo Tang, Wenyang Qian, Anji Yu, Xingbo Zhao, Ho-Meoyng Choi and Chueng-Ryong Ji for valuable discussions. This work was supported in part by the U.S. Department of Energy (DOE) under Grants No. DE-FG02-87ER40371, No. DE-SC0018223 (SciDAC-4/NUCLEI), and No. DE-SC0015376 (DOE Topical Collaboration in Nuclear Theory for Double-Beta Decay and Fundamental Symmetries). This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231.
© 2019 American Physical Society.