1. η and π0 Decay to Two Neutrinos
Ali R. Fazely
Department of Physics
Southern University
Miami Conference, 2008
December

2. In collaboration with Richard L. Imlay, Samvel Ter-Antonyan, Xianwu Xu
Department of Physics
Southern University

3. Do η or0 decay into two neutrinos?
Standard Model: 0  νν or η  νν is forbidden, except for massive neutrinos.
The experimental search for such purely NC decays would shed light on the nature of neutrinos and weak processes.

4. Weak Current The +  e + + e has a BR of 1.23  10-4 (pdg)
The helicity is broken due to the mass of the electron consistent with the V-A interaction.

5. o   Forbidden in V-A Interaction o is 0- and vacuum is 0+
For massless neutrinos
0-  0+ transition is
allowed only if Pseudoscalar (P) is present
Same for   

6. The rate for A and P
The decay rate for A interaction is proportional to (1 -  ). For massless neutrinos  = 1 and the rate is zero.
The decay rate for P interaction is proportional to (1+  ). For massless neutrinos  = 1 and the rate is maximum.

7. The rate for A and P
A-coupling:
BR = π → eνe/π → μνμ = (me/mμ)2[1/(1- mμ2/mπ2)2] = 1.275×10-4
P-coupling:
BR = π → eνe/π → μνμ = 1/(1- mμ2/mπ2)2 = 5.5

8. Experimental results on η  νν and 0  ννq Z0
Within the SM, the
diagram is a simple
qq annihilation to
lepton pairs through a
Z0 propagator. l- q-

9. Arnellos, Marciano, Parsa, Nucl Phy B196 (1982)
Decay Rate
Arnellos, Marciano, Parsa, Nucl Phy B196 (1982)

10. Experimental Results
LSND
pdg, all at 90% CL

11. 8.7 ± 6.3 (stat) ± 2.4 (syst) beam-excess events (pdg)
LSND Results
PRL 92, 4, , hep-ex/
Observation of a muon-like, beam-excess above 160 MeV in the LSND detector
8.7 ± 6.3 (stat) ± 2.4 (syst) beam-excess events (pdg)
The possible Branching Ratio of is:

12. π0  ντντ
A 95% CL, upper limit of <18.2 MeV was set by the ALEPH Collaboration on ντ mass from 3 and 5-prong τ decay. (Eu J Phys, 1998, pdg). However, (mτ/m)2 < /(134.9)2 ≈

13. π0  ντντ Therefore, A possible laboratory to set limits on the ντ
Γ(π0  ντντ)/Γ(π0  all) < 5.0 × 10-10,
assuming no exotic mechanisms!
A possible laboratory to set limits on the ντ
mass!

14. η  νν
(90%CL)
pdg, BES2 collaboration, 06Q PRL

21. Electrons/positrons
Photons, from 0 and η
muons
neutrons

22. Estimates for the BR of the km3 Detectors, e.g. IceCube
Dominant interaction inside the ice is:
The signature is an electron or τ cascade event

23. Primary Flux Solid and dashed lines are those of Gaisser & Honda, (hep-ph/ (2002)). Symbols are from spectra of Wiebel, Bierman & Meyer, Ast. And Astrophys. 330 (1998), used in our CORSIKA simulations

24. The IceCube Detector

25. Atmospheric Neutrino Flux, CORSIKA

26. Integral Spectra

27. Geant-3.21 Simulation

28. Branching Ratio vs. Energy, 5-year run

29. Conclusions Limits can be set for the first time on ηνν
with km3 detectors
νν limits would not be competitive with existing limits.
Dedicated experiments can be designed to look for ντντ yielding limits on
the ντ mass as well as any possible P interaction in NC sector.