Abstract
We discuss the role of meson exchange mechanisms in γγ→γγ scattering. Several pseudoscalar (π0, η, η′(958), ηc(1S), ηc(2S)), scalar (f0(500), f0(980), a0(980), f0(1370), χc0(1P)) and tensor (f2(1270), a2(1320), f2′(1525), f2(1565), a2(1700)) mesons are taken into account. We consider not only s-channel but also for the first time t- and u-channel meson exchange amplitudes corrected for off-shell effects including vertex form factors. We find that, depending on not well known vertex form factors, the meson exchange amplitudes interfere among themselves and could interfere with fermion-box amplitudes and modify the resulting cross sections. The meson contributions are shown as a function of collision energy as well as angular distributions are presented. Interesting interference effects separately for light pseudoscalar, scalar and tensor meson groups are discussed. The meson exchange contributions may be potentially important in the context of a measurement performed recently in ultraperipheral collisions of heavy ions by the ATLAS collaboration. The light-by-light interactions could be studied in future in electron–positron collisions by the Belle II at SuperKEKB accelerator.
Highlights
In the Standard Model the light-by-light scattering is usually assumed to proceed through lepton, quark and W gauge boson loops [1,2,3,4]
In [6] we considered in addition two-gluon exchange contribution
In [12] the authors formulated light-by-light scattering sum rules, that lead to relations between the γ∗γ transition form factors for C-even scalar, pseudoscalar, axial-vector and tensor mesons when assuming sum rule saturation
Summary
In the Standard Model the light-by-light scattering is usually assumed to proceed through lepton, quark and W gauge boson loops [1,2,3,4]. In [6] we considered in addition two-gluon exchange contribution This mechanism, in contrast to the VDM-Regge one survives to larger scattering angles. In the present paper we shall consider several pseudoscalar (JPC = 0−+), scalar (JPC = 0++), and tensor (JPC = 2++) meson exchange contributions for the γγ → γγ elastic scattering. In [12] the authors formulated light-by-light scattering sum rules, that lead to relations between the γ∗γ transition form factors for C-even scalar, pseudoscalar, axial-vector and tensor mesons when assuming sum rule saturation. We expect that for the t and u diagrams the corresponding form factors can be rather hard (larger cut-off parameter) compared to purely hadronic processes as they describe the coupling of space-like meson to semi point-like objects (photons)
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