η and π 0 decay to two neutrinos
DESCRIPTION
η and π 0 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? - PowerPoint PPT PresentationTRANSCRIPT
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.