and p0 Decay to Two Neutrinos

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? and p0 Decay to Two Neutrinos
Ali R. Fazely Department of Physics Southern
University Miami Conference, 2008 December 16
-21
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In collaboration with
Richard L. Imlay, Samvel Ter-Antonyan, Xianwu
Xu Department of Physics Southern University
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• Do ? or?0 decay into two neutrinos?
• Standard Model ?0 ? ?? or ? ? ?? 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 Interaction ?o is
0- and vacuum is 0 For massless neutrinos 0-
? 0 transition is allowed 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 p ? e?e/p ? µ?µ (me/mµ)21/(1-
  mµ2/mp2)2 1.27510-4
• P-coupling
• BR p ? e?e/p ? µ?µ 1/(1- mµ2/mp2)2
  5.5

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Experimental results on ? ? ?? and?0 ? ??
l
q
Z0
Within the SM, the diagram is a simple qq
annihilation to lepton pairs through a Z0
propagator.
l-
q-
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Decay Rate
Arnellos, Marciano, Parsa, Nucl Phy B196 (1982)
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Experimental Results
LSND
pdg, all at 90 CL
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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

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p0 ? ?t?t

• A 95 CL, upper limit of lt18.2 MeV was set
  by the ALEPH Collaboration on ?t mass from 3 and
  5-prong t decay. (Eu J Phys, 1998, pdg).
• However,
• (mt/m?)2 lt 331.24/(134.9)2 0.0182

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p0 ? ?t?t

• Therefore,
• G(p0 ? ?t?t)/G(p0 ? all) lt 5.0 10-10,
• assuming no exotic mechanisms!
• A possible laboratory to set limits on the ?t
• mass!

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? ? ??
(90CL) pdg, BES2 collaboration, 06Q PRL 97
202002
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muons
neutrons
Photons, from ?0 and ?
Electrons/positrons
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Estimates for the BR of the km3Detectors, e.g.
IceCube

• Dominant interaction inside the ice is
• The signature is an electron or t cascade event

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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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The IceCube Detector
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Atmospheric Neutrino Flux, CORSIKA
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Integral Spectra
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Geant-3.21 Simulation
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Branching Ratio vs. Energy,5-year run
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Conclusions

• Limits can be set for the first time on ????
• with km3 detectors
• ???? limits would not be competitive with
  existing limits.
• Dedicated experiments can be designed to look for
  ???t?t yielding limits on
• the ?t mass as well as any possible P
  interaction in NC sector.