Neutrino Reactions in the Heavy Water

The SNO detector is unique in its use of heavy water as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis from the measurements of the neutrino flux. SNO provides the ability to measure both the flux and the energy spectrum of the electron neutrinos with the direct reconstruction of charged-current events.

Other reactions, such as neutral-current events and electron-scattering events, are sensitive to all flavours of neutrino. Thus, the flux of non-electron neutrinos can be inferred from the difference between the total neutrino flux and the electron neutrino flux. A non-zero flux of non-electron neutrinos is an unambigous indication of solar neutrino oscillations!

 

Charged-Current Rection

As the neutrino approaches the deuterium nucleus a W boson is exchanged between the electron neutrino and a d quark in the neutron.

This changes the neutron in the deuterium to a proton, and the neutrino to an electron.

The electron will emit Cherenkov radiation and this cone of light will be detected by the photomultiplier tube array of SNO.

The energy spectrum of electron neutrinos will show a distortion from the theoretical shape if solar neutrinos oscillate.

 

Neutral-Current Reaction

The mediator of the neutral current reaction is the neutral Z boson.

The interaction breaks the deuterium nucleus and liberates the proton and the neutron.

The neutron will then be thermalized in the heavy water as it scatters around.

It will eventually be observed due to gamma rays which are emitted when it is captured on deuterium or on Chlorine (as shown here)

The gamma rays will scatter electrons which produce detectable light via the Cherenkov process. The neutral-current events are equally sensitive to all three neutrino types.

 

Electron Scattering Reaction

The electron-scattering reaction is not unique to heavy water and it is the primary mechanism in other light water detectors.

The interaction is sensitive to all neutrino flavours, but the scattering probability of an electron-neutrino is about a factor of six larger than the scattering probability of the two other neutrino types.

The direction of the electron is a good directional probe of the incident electron even if the final state energy is shared between the electron and the neutrino.