η and π0 Decay to Two Neutrinos Ali R. Fazely Department of Physics Southern University Miami Conference, 2007

In collaboration with Richard L. Imlay, Samvel Ter-Antonyan, Kevin Muhammad Department of Physics Southern University

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.

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.

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   

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.

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

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

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

Experimental Results LSND pdg, all at 90% CL

8.7 ± 6.3 (stat) ± 2.4 (syst) beam-excess events (pdg) LSND Results PRL 92, 4, 091801-1, hep-ex/0310060 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:

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 < 331.24/(134.9)2 ≈ 0.0182

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!

η  νν (90%CL) pdg, BES2 collaboration, 06Q PRL 97 202002

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

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

Primary Flux Solid and dashed lines are those of Gaisser & Honda, (hep-ph/0203272 (2002)). Symbols are from spectra of Wiebel, Bierman & Meyer, Ast. And Astrophys. 330 (1998), used in our CORSIKA simulations

Atmospheric Neutrino Flux, CORSIKA

Detected Spectra

Branching Ratio vs. Energy, 5-year run

Branching ratio vs. Years

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.