Atmospheric Neutrino
Anomaly
By
Tasneem Mohsinally
History
Neutrino 
- predicted by Pauli (1930’s) to explain
energy conservation in beta decay
- neutral, spin 1/2
- 3 flavours: e  
- weak force (short range)
W, Z
Standard Model
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?
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
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
Neutrino Oscillations
Mixing relationship between flavour and mass eigenstates:
Allowing the mass states to propogate at different frequencies
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.
Super Kamiokande (1996)
-
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
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
-
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
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
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).
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
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
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