Enhancement of Direct CP Asymmetry in  \(Z'\) Models

We obtain the favored parameter space of CP-violating \(Z'\) models using updated constraints from lepton flavor universality ratios, CP-conserving and CP-violating observables in the \( b \rightarrow s \ell \ell \) sector, \(B_s-\bar{B}_s\) mixing, and neutrino trident production. We consider two types of \(Z'\) models giving rise to new physics scenarios, \(C_9^{\mu \, \mathrm NP} <0\) and \([C_9^{\mu \, \mathrm NP} = -C_{10}^{\mu \, \mathrm NP}, C_9^{e \, \mathrm NP} = -C_{10}^{e\, \mathrm NP}]\) , favored by the current data. We show that the favored \(1\,\sigma \) parameter space of \(Z'\) models generating scenario \(C_9^{\mu \, \mathrm NP} <0\) allows for an enhancement in the integrated \(A_{CP}\) values in \(q^2 =[8,9]\,\mathrm {GeV^2}\) and \(q^2 =[6,7]\,\mathrm {GeV^2}\) bins up to \(\pm 25\%\) and \(\pm 15\%\) respectively. The favored region of \(Z'\) models generating scenario \([C_9^{\mu \, \mathrm NP} = -C_{10}^{\mu \, \mathrm NP}, C_9^{e\, \mathrm NP} = -C_{10}^{e\, \mathrm NP}]\) allows only positive values of \(A_{CP}\) . Hence, a future precise measurement of \(A_{CP}\) in these bins can potentially help in distinguishing between these two \(Z'\) models.