MeasurementIntro

Introduction to the Measurement

The Mu2e Experiment will measure the rate of muons that convert directly into electrons in the field of a nucleus. This is a process that changes the lepton's "flavor", where the flavor signifies the type as electron, muon or tau. While we have seen flavor oscillation in neutrinos---the neutral leptons that also come in three flavors: electron neutrinos, muon neutrinos and tau neutrinos---this is all but forbidden in the standard model for the charged leptons (electrons, muons and taus.) It is suppressed due to the large masses of the charged leptons. The standard model prediction for the conversion rate of a muon directly into an electron is one in approximately every 10^54. Mu2e will be sensitive to measuring a rate of approximately one in every 10^17 muon decays, so if we see a signal it will be a clear sign of physics beyond the standard model.

The Technique

The typical standard model decay of a muon results in three final state particles: a muon neutrino carries "muon" flavor making this a flavor-conserving process, an electron carries the same electric charge making this a charge-conserving process, and an anti-electron neutrino cancels out the electron flavor that was introduced keeping the decay flavor-conserving. The difference between this standard decay and the decay that we are searching for with Mu2e is that our signal process does not result in the production of those two neutrinos. Since neutrinos are notoriously difficult particles to detect, we will use the ideas of conservation of energy and momentum to determine if the muon converted to an electron, or if it proceeded through the standard decay channel and also produced the two neutrinos.

(mono-energetic signature)

Overview of Theories that Mu2e Will Probe

MSSM with right handed neutrinos

SUSY with R-parity Violations

Leptoquarks

New Gauge Bosons

Large Extra Dimensions

Non-Minimal Higgs Structure

A Brief History of the Measurement

The first search for muon to electron conversion was by Lagarrigue and Peyrou in 1952 [1], with many other searches carried out since then [2-9]. In this section we will more briefly describe a few of the more recent searches.

[1] A. Lagarrigue and C. Peyrou, Comptes Rendus Acad. Sci. Paris, 234, 1873(1952). See also J. Steinberger and H. Wolfe, Phys. Rev. 100, 1490 (1955).
[2] M. Conversi et al., Phys. Rev. D122, 687 (1961).
[3] R. Sard et al., Phys. Rev. 121, 619 (1961).
[4] G. Conforto et al., Nuovo Cimento 26, 261 (1962).
[5] J. Bartley et al., Phys. Lett. 13, 258 (1964).
[6] D. Bryman et al., Phys. Rev. Lett. 28, 1469 (1972).
[7] A. Badertscher et al., Phys. Rev. Lett. 39, 1385 (1977).
[8] S. Ahmad et al., Phys Rev. D38, 2102 (1988).
[9] W. Bertl et al., Eur. Phys. J. C47, 337 (2006).