Single-photon events in e^+ e^- collisions

TL;DR

This paper analyzes single-photon production in electron-positron collisions, providing a unified theoretical framework for neutrino and neutralino processes, and explores effects of anomalous couplings and polarization asymmetries.

Contribution

It introduces a generic, factorized amplitude form applicable to both neutrino and neutralino processes, including anomalous couplings, and discusses methods to distinguish these processes experimentally.

Findings

Unified description of neutrino and neutralino single-photon production.

Confirmation of the Dirac-Majorana confusion theorem.

Potential to differentiate processes via polarization and asymmetries.

Abstract

We provide a detailed investigation of single-photon production processes in $e^+e^-$ collisions with missing momenta carried by neutrinos or neutralinos. The transition amplitudes for both processes can be organized into a generic simplified, factorized form; each neutral V$\pm$A vector current of missing energy carriers is factorized out and all the characteristics of the reaction is solely included in the electron vector current. Firstly, we apply the generic form to give a unified description of a single-photon production with a Dirac-type or Majorana-type neutrino-pair and to confirm their identical characteristics as suggested by the so-called Practical Dirac-Majorana Confusion Theorem. Secondly, we show that the generic amplitude form is maintained with the anomalous P- and C-invariant WW$\gamma$ couplings in the neutrino-associated process and it enables us to easily understand large contributions of the anomalous WW$\gamma$ couplings at higher energies and, in particular, at the points away from the Z-resonance peak. Finally, the neutralino-associated process, which receives modifications in both the left-handed and right-handed electron currents due to the exchanges of the left-handed and right-handed selectrons, can be differentiated from the neutrino-associated ones through the left-right asymmetries and/or the circular polarization of the outgoing photon.