Substructuretestswithpolarizede+e-→2γareacrucialexperimentalapproachinhigh-energyphysicstoprobethefundamentalstructureofmatter.Bycollidingpolarizedpositronsandelectrons,researcherscanstudytheangulardistributionandpolarizationdependenceoftheresultingtwo-photonfinalstate.Thisprocessprovidesasensitivetestforpossiblesubstructureorcompositenessofleptons,asdeviationsfromthepredictionsofQuantumElectrodynamics(QED)couldindicatenewphysicsbeyondtheStandardModel.Theuseofpolarizedbeamsenhancesthesensitivitytosucheffectsbyallowingprecisemeasurementsofspin-dependentobservables.ThesetestsareparticularlyimportantforsettinglimitsontheenergyscaleofpossibleleptonsubstructureorcontactinteractionsthatmightariseinvarioustheoreticalextensionsoftheStandardModel.
