Particle Physics: Status and Perspectives Part 8: The Precision Frontier Manfred Jeitler SS 2018

The Frontier

How to find “New Physics” Higher energy produce new real particles “Energy frontier” Higher precision find tiny deviations in measurements via production of virtual particles also needs higher statistics  “Precision frontier” or “Intensity frontier”

The search for Lepton Flavor Violation are lepton numbers really absolutely conserved? they are not for neutrinos! should also be violated for charged leptons? nothing seen so far long series of experiments have been looking for the decay μe (without neutrinos) Sindrum, Sindrum II, MEG at Paul Scherrer Institute looking for μeγ Switzerland new: Mu2e at Fermilab Chicago, USA

(charged lepton flavor violation)

Main background: muon decay in orbit (DIO)

The magnetic moment of the leptons magnetic moment is proportional to angular momentum (spin) factor of proportionality: μB = e h / 2 me “Bohr magneton” derived from classical argument for quantum mechanical particles, according to Dirac equation: μ = g μB s g = “Landé g-factor” just from Dirac equation, g=2

The magnetic moment of the leptons g-factor depends on charge distribution in particle would be 1 for a classical particle with homogeneous charge distribution gproton = 5.59 charge distributed on outside? composite structure of proton (quarks, gluons) for leptons, difference from 2 due to vacuum polarization can be developed by orders of α (fine structure constant, α ~ 1/137) measured values: μe = 1.001’159’652’1859  0.000’000’000’0038 μB μμ  = 1.001’165’920’80  0.000’000’000’63 eħ/2mμ each coupling of a virtual electron-positron pair to a virtual photon introduces another factor of α series diverges, but can be “renormalized” by redefining the (unobservable) charge and mass of “bare” lepton: infinite minus infinite = something finite (an operation you are not usually supposed to do in elementary mathematics) very accurate experimental measurement possible (particles circulate for long times in a magnetic field)

Status on muon anomalous magnetic moment

Calculating the muon anomalous magnetic moment

The discrepancy between theory and experiment 3.6 σ

The Brookhaven muon g-2 experiment

The Brookhaven muon g-2 experiment

The Brookhaven muon g-2 ring on its way to Fermilab

Distribution of electron counts versus time