Characterizing and Mitigating Backgrounds for the MOLLER Experiment

The MOLLER (Measurement Of a Lepton Lepton Electroweak Reaction) experiment at Jefferson Lab

aims to probe new physics by performing an unprecedentedly precise measurement of the parity-

violating asymmetry (APV) in electron-electron scattering. Achieving the desired uncertainty of 0.8

ppb requires a thorough understanding and mitigation of all potential background sources. This

presentation will detail the comprehensive background studies for the MOLLER experiment, which

are crucial for a successful measurement. The backgrounds are broadly classified as reducible and

irreducible. Reducible backgrounds, such as rescattered particles, ferrous-related effects, and pions, are

studied and minimized through extensive simulation campaigns using the remoll framework based on

Geant4. These simulations have guided the optimization of the spectrometer and shielding to ensure

a clean signal. Irreducible backgrounds, primarily from ep elastic and inelastic scattering within the

target, overlap with the Møller signal. We will discuss how the highly segmented main detector and

advanced analysis techniques allow for the deconvolution of these backgrounds from the desired

Møller asymmetry.