Constraints on Muon Decay Parameters from Neutrino Mass

1
Constraints on Muon Decay Parameters from
Neutrino Mass

• Rebecca J. Erwin
• Jennifer E. Kile
• M. Ramsey-Musolf
• Peng Wang
• California Institute of Technology

2
The Big Picture

• Neutrinos have mass new physics!
• Approaches
• number of flavors, mass scale, mixing, Dirac vs.
  Majorana, . . .
• effects on astrophysical and particle physics
  processes. For example . . .
• Can relate ? mass to muon decay
• experimental limits on ? mass ? interesting
  constraints on µ decay parameters

3
Outline

• µ-decay Michel parameters
• parameterize contributions to µ-decay from beyond
  the Standard Model
• Connecting µ-decay and ? mass
• chirality-changing operators that contribute to
  both processes
• operator mixing
• Implications for the TWIST experiment
• ? mass puts strong constraints on some
  contributions to the MPs
• Prézeau and Kurylov, PRL 95 (2005)

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µ-decay Michel Parameters
,
, ...

• Michel parameters (?, ?, d, ?, . . . ) are
  bilinear combinations of the coupling constants g
• Standard Model
• Other gs nonzero in many beyond-the-SM models

5
Connecting µ-decay and ? Mass
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What Goes In Our Calculation

• Different operators contribute to different
  Michel parameters
• Combined with . . .
• Lots of operator mixings ? lots of diagrams

7
What Comes Out Implications for TWIST

• At current experimental limits, any deviation
  from SM values will not come from ? mass!
• Gagliardi, Tribble, Williams, hep-ph/0509069

8
Summary

• Michel parameters describe contributions to
  µ-decay from beyond SM
• Can use experimental limits on neutrino mass to
  constrain the Michel parameters
• Resulting constraints much smaller than current
  experimental limits
• Future research
• Majorana case, ß-decay, . . .