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 or0 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 Interactiono is 0- and vacuum is 0+

For massless neutrinos 0- 0+ transition isallowed 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/mπ

2)2] = 1.275×10-4

• P-coupling:

BR = π → eνe/π → μνμ = 1/(1- mμ2/mπ

2)2 = 5.5

Experimental results on η νν and0 νν

Z0

l-q-

q l+

Within the SM, the diagram is a simpleqq annihilation to lepton pairs through aZ0 propagator.

Decay Rate

82222 103/4 fGF

222/1222222 /)/41(4)(/)( mmmfmGall F

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

2/122228 )/41(/103)(/)( mmmmall

Experimental Results600 107.1)(/)( allee

6106.1)(/)( all

600 101.2)(/)( all

700 107.2)(/)( all

pdg, all at 90% CL

LSND

• 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:__

0

70__

0 10)(3.3)(6.44.6)(/)( syststatall

LSND Results PRL 92, 4, 091801-1, hep-ex/0310060

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,

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

4106)(

)(

all

invisible

(90%CL)

pdg, BES2 collaboration, 06Q PRL 97 202002

Photons, from 0 and η

muons neutronsElectrons/positrons

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

XeOe ,16,

Primary FluxSolid 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 ηνν with KM3 detectorsνν 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.