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Atmospheric Neutrino Anomaly

Atmospheric Neutrino Anomaly. By Tasneem Mohsinally. History. Neutrino  - predicted by Pauli (1930’s) to explain Standard Model energy conservation in beta decay - neutral, spin 1/2 - 3 flavours: e   - weak force (short range) W, Z.

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Atmospheric Neutrino Anomaly

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  1. Atmospheric Neutrino Anomaly By Tasneem Mohsinally

  2. History Neutrino  - predicted by Pauli (1930’s) to explain Standard Model energy conservation in beta decay - neutral, spin 1/2 - 3 flavours: e   - weak force (short range) W, Z

  3. Solar Neutrino Puzzle - < 20MeV - 400 billion per second per square inch Raymond Davis Homestake Experiment (1970’s) - chlorine based detector - ~5000 ft underground - each neutrino interaction resulted in argon atom production. Confirmed sun produces neutrinos Only one third the number of neutrinos predicted by theory were detected Where were the rest?

  4. Atmospheric Neutrino Anomaly • Cosmic Rays hitting the earth’s atmosphere • Spray of secondary particles decay resulting in neutrinos • Expected  : e = 2 : 1 IMB experiment (1985) Kamiokande II Soudan observed  to e interactions was closer to one  coming from the far side of the earth were depleted by about one half compared to those coming from the atmosphere overhead. alternative explanations could not convincingly fit the results found

  5. Neutrino Oscillations Neutrinos do not propagate as a single wave but as a pre-packaged combination of two mass eigenstates - neutrino is composed of two different masses! - different periodicities in one phase the pair may act as a muon neutrino and when shifted 90 degrees may make a tau neutrino

  6. Neutrino Oscillations Mixing relationship between flavour and mass eigenstates: Allowing the mass states to propogate at different frequencies

  7. Neutrino Oscillations Probability for a muon neutrino changing into a tau neutrino: Mixing probability α mass difference squared If neutrinos have different (non-zero) masses and if they mix so that each neutrino represents a mixture of two or more different masses, Neutrino oscillations will occur.

  8. Proton decay, solar neutrinos, atmospheric neutrinos Estimated 2:1 flux ratio of muon to electron neutrinos Detector - 2000 ft. underground - 50,000 tonne tank of ultra-pure water - ~12,000 photomultiplier tubes Super Kamiokande (1996)

  9. Neutrino Interaction - strikes a quark in an oxygen nucleus, snatches a charge becoming either muon or electron - energetically charged elementary particle emits Cherenkov radiation Cherenkov radiation: direction of outgoing particle correlated to direction of neutrino high energies ~ 15° Amount of light radiated is a measure of neutrino energy

  10. High Acquisition rate ~ 100 triggers per second Partial analysis of events is done as they arrive and then sent to a laboratory outside the mine via fiber optics where fully contained events are identified by a pattern recognition algorithms and filtered into different analysis streams for immediate processing. • Single ring events ~ 5.5 per day • ~ 98% accuracy

  11. Super K data indicated atmospheric neutrino anomaly due specifically to a deficit in muon neutrinos - significant up/down asymmetry Neutrino flux should be equal for equal angles with the zenith Observations showed depletion of muon neutrinos travelling in from far side of the earth versus those coming in from the atmosphere overhead

  12. This graph is a preliminary result based on the current full data-set; details of the analysis of high energy events based on the first 414 days of data were published in Phys. Lett. B436(1998)p.33 (hep-ex/9805006).

  13. This deficit as a function of energy and arrival angle indicates that muon neutrinos oscillate to some other flavour Probability of oscillation is related to the distance travelled by the neutrino from its point of production to detection • Oscillate with Tau neutrinos • Economic • Pi-zero events

  14. Implications • Standard model • Revise current model • Unified theory • Contribution to mass in the universe • ~ 50 billion neutrinos per electron • Big Crunch / Cool Expansion • Majorana neutrino • Travel slower than c • Predicts a reversal in chirality • Violations of lepton number

  15. References Neutrino Oscillation; http://hep.bu.edu/~superk/osc.html Neutrino oscillation; (2007, November 22). In Wikipedia, The Free Encyclopedia. Retrieved 03:40, December 2, 2007, from http://en.wikipedia.org/w/index.php?title=Neutrino_oscillation&oldid=173036786 Discovery of Neutrino Mass and Oscillations; http://www.phys.hawaii.edu/~jgl/nuosc Solar Energy Generation Theory tested at Brookhaven National Laboratory; http://www.bnl.gov/bnlweb/raydavis/research.htm Atmospheric Neutrinos; http://hep.bu.edu/~superk/atmnu/ Super Kamiokande; http://www.ps.uci.edu/~superk/neutrino.html Neutrino Mass; http://universe-review.ca/R15-13-neutrino.htm

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