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Neutrino Mass

By Ben Heimbigner

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Overview of the Presentation

• History of the Neutrino

• Neutrino Oscillations and the relation to mass.

• Observations of Neutrinos– Super Kamiokande (Super K)– Sudbury Neutrino Observatory (SNO)

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What is a Neutrino?

• Fundamental particle belonging to the Lepton family

• Predicted 1930 by W. Pauli and first observed in 1956.

• No Strong or Electromagnetic reaction along with a very small mass make them hard to detect.

• Three types also called flavors: Electron Muon and Tau.

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Solar Neutrino Problem

• First Noticed in the 1960’s by Ray Davis– Used a large tank of Perchloroethylene and observed

the conversion of chlorine to radioactive argon– Major Disagreement (30% of predicted value)

between the predicted neutrino numbers that should be reaching earth and the measured values.

• At the time it was uncertain what was causing this major disagreement between theory and experiment.

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Current Detection of Neutrinos• Cherenkov Radiation

– Interaction between sub atomic particles in water and Neutrinos.

• Caused when a particle goes faster than the speed of light within a medium. The electron moves faster than its electric field can propagate similar to a sonic boom.

– Common example is when a neutrino hits an electron in water.

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Other Methods of Detecting Neutrinos

• Radiochemical– Rely on the neutrino interacting with a particle

and changing it into something else such as Chlorine into Argon.

• Scintillation– Particle is absorbed by the substance and

then substance fluoresces at specific known wavelengths.

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Why Does Neutrino Oscillation mean Neutrino Mass.

• The two properties are intrinsically related– If Neutrinos are oscillating it means they must

have mass.

• This flavor oscillation is caused because the neutrinos can’t be in an eigenstate for energy and mass at the same time.– This causes the Neutrinos to have flavor

oscillations.

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Neutrino Oscillation MathWe start out with two equations describing the Neutrinos states. Va describes the flavor, either electron, muon or tau. Vi describes the neutrino mass, 1, 2 or 3.

Sense Vi are mass eigenstates we can describe their propagation by standard plane wave solutions:

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Neutrino Oscillation ContIf we use the ultra relativistic case we can describe Ei from the previous equation as:

Inserting that into our previous equation we have:

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Derivation FinishedFrom the Previous equation we can find out the probability that a neutrino of one flavor will oscillate into a different flavor

What’s most important for us is that this term is dependent on the squared difference of masses between the two flavors. This means for there to be oscillations there needs to be neutrino mass.

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How do we Know they are oscillating?

• 1998 Super-Kamiokande – Detection of Similar numbers of Muon and

Electron Neutrinos instead of 2:1 ratio predicted.

• Indicated that some of the Muon neutrinos were oscillating into Tau neutrinos.

• Sudbury Neutrino Observatory (SNO)– Sensitive to electron and total neutrino flux.

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Why is Neutrino Mass a big deal?

• In the Standard Model Neutrino’s were considered to be Massless.– However they have been found to have a

mass this presents us with physics that are outside the realm of the Standard Model.

• Previous to recent experiments all other observations had supported that neutrino’s had zero mass.

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Details on Super K

• Massive 50,000 ton cylinder of pure water

• Located 1000m underground within a mine so as to isolate the environment from outside interference such as cosmic rays.

• 11,200 Photomultiplier tubes contained within for detection of light from Cherenkov radiation.

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Super Kamiokande Experiment

• Super-K is a water imaging Cherenekov detector. – Neutrino comes in and hits an electron

creating Cherenekov radiation– Photomultiplier tubes surrounding the water

tank then pick up the light emitted from Cherenekov radiation.

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Outside View of Super K

• Picture From: http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html

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Super Kamiokande

Photo from: http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html

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Super-K Findings

• They found that there was strong evidence point towards a muon to tau neutrino oscillation from their atmospheric results instead of other possibilities such as sterile neutrinos or no oscillations.

• The solar model also found evidence although less direct of neutrino oscillations from the night day differences.

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SNO

• 9600 PMT’s

• Located 2070 meters below ground in Creighton mine.

• 1000 tons of heavy water.

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SNO Detector

SNO Detector viewed from the bottom, it is 12 meters in diameter.

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SNO Experiment

• Able to detect three different reactions.

Elastic Scattering (ES)

Neutral Current (NC)

Charged Current (CC)

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SNO Results

• By measuring all three reactions they were able to find that there was an excess of Neutral current flux over the elastic scattering and charged current. This means that there is an excess of total neutrinos (measured by NC) compared to electron neutrinos (measured by charged current).

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Sources

Super K Web Site: http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html

• SNO Website: http://www.sno.phy.queensu.ca/

• http://www.ps.uci.edu/~superk/oscillation.html

• Theory Of Neutrino Oscillations (http://www.citebase.org/fulltext?format=application%2Fpdf&identifier=oai%3AarXiv.org%3Ahep-ph%2F0409230)

• http://www-sk.icrr.u-tokyo.ac.jp/sk/pub/koshio-proc.pdf

• http://www-sk.icrr.u-tokyo.ac.jp/sk/pub/svoboda-tau2000.pdf

• Various Wikipedia articles.