Searching for $Z'$ bosons at the P2 experiment

TL;DR

The P2 experiment can detect or constrain new $Z'$ gauge bosons through parity-violation measurements in electron scattering, covering a wide mass range and improving existing limits, especially for light and heavy $Z'$ models.

Contribution

This work evaluates the sensitivity of the P2 experiment to various $Z'$ models, demonstrating its potential to discover or constrain new gauge bosons beyond current limits.

Findings

P2 can probe $Z'$ gauge couplings down to $10^{-5}$ for light $Z'$ bosons.

P2 can explore $Z'$ masses up to 79-90 TeV depending on the target nucleus.

Sensitivity to mass mixing angles can be below $10^{-4}$, depending on model parameters.

Abstract

The P2 experiment aims at high-precision measurements of the parity-violating asymmetry in elastic electron-proton and electron-$^{12}$C scatterings with longitudinally polarized electrons. We discuss here the sensitivity of P2 to new physics mediated by an additional neutral gauge boson $Z'$ of a new $U(1)'$ gauge symmetry. If the charge assignment of the $U(1)'$ is chiral, i.e., left- and right-handed fermions have different charges under $U(1)'$, additional parity-violation is induced directly. On the other hand, if the $U(1)'$ has a non-chiral charge assignment, additional parity-violation can be induced via mass or kinetic $Z$-$Z'$ mixing. By comparing the P2 sensitivity to existing constraints, we show that in both cases P2 has discovery potential over a wide range of $Z'$ mass. In particular, for chiral models, the P2 experiment can probe gauge couplings at the order of $10^{-5}$ when the $Z'$ boson is light, and heavy $Z'$ bosons up to 79 (90) TeV in the proton ($^{12}$C) mode. For non-chiral models with mass mixing, the P2 experiment is sensitive to mass mixing angles smaller than roughly $10^{-4}$, depending on model details and gauge coupling magnitude.