Speaker
Description
Mu2e experiment at Fermilab will search for the process of neutrino-less $\mu^- \to e^-$ conversion on Al. The signature of this process is a monocromatic electron with the energy of 104.97 MeV. The systematic uncertainty on the reconstructed electron momentum, $\sigma_P$, is required to be $\le$ 100 keV/c. For that, the momentum scale of the experiment has to be known with the relative accuracy better than $10^{-3}$.
Calibrating the momentum scale using Michel decays of stopped positive muons, $\mu^+ \to e^* \nu \nu$, or $\pi^- \to e^- \nu$ decays of stopped negative pions involves reducing the magnetic field in the detector, determining the momentum scale at a lower field, and extrapolating the scale back to the nominal field.
We describe an experimental technique which avoids uncertainties related to the scale extrapolation. It relies on the reconstruction of E = 129.4 photons produced in the process of radiative $\pi^-$ capture on hydrogen, $\pi^- p \to n \gamma$, and converted into $e^+e^-$ pairs in a photon converter located in the upstream part of the detector.
Together, measurements of the three physics processes should provide a reliable calibration of the Mu2e momentum scale.
