Neutrinos atmospheric

Super-Kamiokande light-water experiment reveals atmospheric neutrino oscillations. 

Trillions of neutrinos are flying through your body as you read this. Created by the Big Bang, stars, and the collision of cosmic rays with the earth s atmosphere, neutrinos outnumber electrons and protons by 600 million to 1. [For more information, see. Gibbs, W. (1998) A massive discovery. Scientific American. August, 279(2) 18-19.]... 

Neutrino oscillations have up to now been detected in two systems. Atmospheric muon neutrinos, which originate from the collision of cosmic rays... 

Fukuda, Y., et al. [Super-Kamiokande Collaboration] 1998. Evidence for oscillation of atmospheric neutrinos, Phys. Rev. Lett.81, 1562 Fukugita, M., Hogan, C. J., Peebles, P. J. E. 1998. The Cosmic Baryon Budget, ApJ503, 518... 

Although I will not discuss the subject here, The most important secondary cosmic-ray flux is the atmospheric neutrino beam because of the discovery of neutrino oscillations by Super-Kamiokande (Fukuda el al., 1998). The experimental situation is reviewed by Kajita Totsuka, 2001 and Jung el al., 2001, and the calculations by Gaisser Honda, 2002. 

Figure 2. Detection principle of an underwater neutrino telescope. Astrophysical neutrinos can reach the Earth and interact in water or in rocks generating an upgoing muon. An array of 5000 optical detectors tracks Cerenkov photons generated along the muon track. A water shielding > 3000 m is effective to reduce the atmospheric fi background, allowing the reconstruction of upgoing muon tracks.

Search for GRB Neutrinos. The AMANDA GRB search for correlated v emission relies on temporal (typically less than 100 s in duration) and angular information provided by BATSE and other satellites in the IPN network (Hurley et al., 1998). Initial search strategies for data collected between 1997-2000 (Hardtke et al., 2003) and for individual GRBs (Stamatikos et al., 2004), have assumed nearly concurrent emission within the duration of prompt gamma-ray emission (Tgo). A new search (Kuehn et al., 2004) also scans for neutrino emission prior to the Tgo start time. No excess was observed for either search method above the expected background from atmospheric v and poorly reconstructed... 

UHECRs are attractive because of their high centre-of mass energy. The proton-nucleon cross section for BH formation is very small compared to other hadronic processes. The neutrino-nucleon cross section for BH formation may be higher than the SM process, thereby giving interest to neutrino interaction. However, rate counting is not sufficient to prove black hole formation in the atmosphere. Discovery of BHs in UHECRs requires discrimination of BH and SM air showers. The extensive air shower (EAS) characteristics of these processes will differ, and with new detector methods and enough statistics expected from the new generation cosmic ray observatories, it may be possible to detect BH-induced EASs. 

Few of the pions formed in the annihilation process reach the earth s surface. They undergo radioactive decay (life-time about 10 s) to muons and neutrinos, or they collide with other particles in the atmosphere and are annihilated. The muons have properties similar to the electron, but are unstable, decaying with a life-time of about 2 x lO s to electrons and neutrinos. The collision reactions of the pions result in the formation of a large number of other particles such as electrons, neutrons, protons, and photons. Some of the electrons so formed are captured in a thick zone around the earth known as the inner van Allen belt. 

Underground detectors observing neutrinos produced by cosmic rays in the atmosphere have measured a v i/ve > 3tio much less than expected and also a deficiency of upward going compared to downward. This could be explained by oscillations leading to the disappearance of Va with Am ... 

The reason why the laboratory was built inside a mountain is that 1400 meters of rock are a perfect filter to screen huge number of particles that hit the land surface these particles are produced by the interaction of cosmic primary rays with the atmosphere s atoms. Muons (particles with positive charge and mass 200 times that of electrons) and neutrinos are the particles that are able to cross this filter. Solar and stellar neutrinos are studied in the Laboratory of Gran Sasso. 

Thus there is now compelling evidence that solar, reactor, atmospheric, and accelerator neutrinos change their flavor from one to another. 

Recently, these findings have been combined with the results of the so-called atmospheric neutrino anomaly, where p-neutrinos generated in pion decays oscillate over into, mainly, r-neutrinos. In addition, terrestrial experiments performed with neutrino fluxes (produced either at nuclear power plants or with accelerators) provide substantial information on the mixing pattern among the different neutrino species. Searches for possible oscillations into further light neutrino flavors, which would be of clear cosmological significance, have not yet provided a clear answer to the question of their existence. (See Sect. 10.8.2 in Chap. 10, Vol. 1)... 

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