Novel Azimuthal Observables from Two-Photon Collision at e^{+}e^{-} Colliders

Area of Science:

• High-energy physics
• Quantum chromodynamics
• Particle physics

Background:

• Exclusive hadron production via two-photon fusion is a key process at electron-positron colliders.
• Understanding photon-induced reactions provides insights into fundamental interactions and particle properties.

Purpose of the Study:

• To introduce novel azimuthal-angle-related observables for exclusive hadron production.
• To analyze the γγ→ππ process as a benchmark for two-photon fusion.
• To explore the potential of these observables for future experimental measurements.

Main Methods:

• Utilizing the transverse-momentum-dependent factorization framework.
• Incorporating linearly polarized quasireal photons emitted from electron and positron beams.
• Employing helicity amplitudes derived from partial wave solutions in dispersion relations for numerical analysis.

Main Results:

• Prediction of a significant cos2ϕ azimuthal asymmetry in dipion production.
• The predicted asymmetry can reach up to 40% under typical experimental conditions (Belle 2, BESIII).
• The study highlights the feasibility of measuring this asymmetry.

Conclusions:

• Accurate measurement of the predicted azimuthal asymmetry can enable direct extraction of the relative phase between specific helicity amplitudes.
• This information is crucial for dispersive determination of hadronic light-by-light contributions.
• The proposed observables offer a new avenue for probing fundamental physics at future colliders.