Four Roads to the neutrino magnetic moment

1
Four Roads to the neutrino magnetic moment

• Traditional ? e cross section
• Cerenkov Radiation
• Transition Radiation
• Resonant Cavities

2
Origin of the Magnetic Moment

• Actually, the effective moment µeff
  (µ2d2)1/2
• also R-parity violating SUSY
• limited to lt10-10 µB expected 109 smaller yet
• If neutrinos are massive, then to first order, µ
  linearly dependent on neutrino mass (?)

c.f. Lee and Shrock,PRD 16 1444 (1977)or
Marciano and
Sanda,Phys Lett 67B 303 (1977)
3
Road OneThe ? e cross section
c.f. Miranda, Segura, Semikoz, and Valle,
hep-ph/9906328

• Traditional approach followed by NuMu, HELLAZ,
  etc. SM EM

4
Calculation of ? e cross section

• High neutrino E does not help
• Quadratic dependence on mag moment
• Need a dedicated detectoryet cant do much
  better than others

5
Road 2Cerenkov Radiation

• K.McF. 1 km long water tank
• Quadratic in µ
• Numerical calculation for 2E20 0.00033 photons
  per year

c.f. Grimus and Neufeld,Phys Lett B315 129 (1993)
6
Road 3Transition Radiation

• From solar neutrino calculationsc.f. Grimus and
  Neufeld hep-ph 9410245
• Still quadratic in µ
• Numerical calculation for 2E20, 1E6 foils4.5E-5
  X-ray photons per year This is a hard
  calculation!The conversion factors are not
  smallnonetheless this should be the final
  answer for given input

Several approximations here
7
Small Adjustments, big gains?

• Small gains from ?p in standard materials. (?)We
  dont have the usual limits a TRD would
  have.Still prefer to avoid X-ray attenuation
  i.e. high Z materials.
• Lowering X-ray detection threshold from 20 keVto
  5 keV gives you a factor of 100 but low
  efficiency in real detectors
• Originally I was looking at a big reactor2
  meters away I think I still am.

8
Road 4The Resonant Cavity
Thanks Fritz DeJongh C.f. Vannucci, hep-ex
9911025

• Essentially a low-energy photon target
• Stimulate radiative decays
• Rotate neutrinos to sterile statesby
  introducing a relative phase to the helicity
  componentsthus reducing the event rate at a
  detector when the cavity is powered-up.
• NOT quadratic in µ!

I havent thoughtabout this yet
9
Resonant Cavity the only remaining option?

• Its at least as attractive as the others!
• There exists a CERN proposal for this
  one.(Vanucci Achievable limits)
• Does not require a dedicated detector
• Detector systematics cancel

10
Four Difficult Roads

• I recommend the traditional search only if it
  comes for free.
• Cerenkov is out
• TR looks bad, at least at NuFact Any
  ideas are welcome!
• More to come on ResCav