Experimental resolvability of TPE-sensitive null observables

Determine whether either of the two charge-conjugate, TPE-sensitive null observables—the forward-backward asymmetries of the hyperon transverse polarization P_y and spin correlation C_{xz} in near-threshold e^+e^-→Λ\bar{Σ}^0+c.c. production—can be experimentally resolved.

Background

The paper studies two-photon-exchange effects in the near-threshold production of Λ and Σ0 hyperons. Differences between polarization and spin-correlation observables in the charge-conjugate channels vanish in the one-photon approximation and therefore provide direct probes of TPE contributions.

At q2=2.396 GeV, the authors predict forward-backward asymmetries for P_y and C_{xz}, but the allowed theoretical band generated by varying the hadronic form-factor cutoffs is broad. Consequently, the calculation does not determine whether the predicted null-observable signals are large enough to be measured experimentally; improved neutral-hyperon form-factor information or constraints from diagonal spin correlations are identified as ways to reduce the uncertainty.

References

With the present cutoff variation, the theoretical band is too broad to establish whether either null observable can be resolved experimentally.

— Strange Two-Photon Exchange in Time-Like Electromagnetic Form Factors  (2609.19652 - Cao et al., 17 Sep 2026) in Section 4.2, “The threshold region”