CompEx II: A Pathway in Search of BSM Physics using Compton Scattering

TL;DR

This paper explores using Compton scattering at Jefferson Lab to test for BSM physics, constraining vacuum refractive index and Lorentz symmetry violations, with future prospects at higher energies and facilities like the ILC.

Contribution

It introduces a novel experimental approach using Compton scattering to set new constraints on BSM theories and Lorentz symmetry violations, with plans for improved measurements at higher energies.

Findings

Constraint on vacuum refractive index: (n-1) < 1.4 × 10^{-8}

Limit on MSME parameters: √(κ_X^2 + κ_Y^2) < 8.6 × 10^{-10}

Future measurements aim to improve sensitivity by a factor of 4-8

Abstract

Constancy and anisotropy of vacuum refractive index serves as a strong way to probe the predictions of theories beyond the standard model (BSM), especially those that predict breaking of local Lorentz and CPT symmetries. For photons of energies in the ranges $9-46$ MeV using a $1.16$ GeV electron beam, a constraint on vacuum refractive index, $(n-1) < 1.4 \times 10^{-8}$ was imposed using the Compton polarimeter in Hall - C of Jefferson Lab (JLab). Absence of sidereal modulation of the vacuum refractive index was then used to constrain the Minimal Standard Model Extension (MSME) parameters of $\sqrt{\kappa_X^2 + \kappa_Y^2} < 8.6 \times 10^{-10}$. These preliminary set of measurements will be followed up by measurements using the $11$ GeV electron beam at JLab with a sensitivity better than current leading constraints by a factor of $4-8$. Furthermore, quantum gravity models predict crystalline nature of space at Planck scales which may manifest as vacuum birefringence that can be probed by Compton scattering using circularly polarized light. We show that future facilities such as the ILC provide tantalizingly interesting possibilities.