Download - η and π 0 Decay to Two Neutrinos
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η and π0 Decay to Two Neutrinos
Ali R. Fazely
Department of Physics
Southern University
Miami Conference, 2007
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In collaboration with
Richard L. Imlay,
Samvel Ter-Antonyan,
Kevin Muhammad
Department of Physics
Southern University
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• 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.
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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.
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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
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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.
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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
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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.
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Decay Rate
82222 103/4 fGF
222/1222222 /)/41(4)(/)( mmmfmGall F
Arnellos, Marciano, Parsa, Nucl Phy B196 (1982)
2/122228 )/41(/103)(/)( mmmmall
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Experimental Results600 107.1)(/)( allee
6106.1)(/)( all
600 101.2)(/)( all
700 107.2)(/)( all
pdg, all at 90% CL
LSND
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• 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
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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
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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!
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η νν
4106)(
)(
all
invisible
(90%CL)
pdg, BES2 collaboration, 06Q PRL 97 202002
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Photons, from 0 and η
muons neutronsElectrons/positrons
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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,
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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
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Atmospheric Neutrino Flux, CORSIKA
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Detected Spectra
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Branching Ratio vs. Energy,5-year run
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Branching ratio vs. Years
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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.