Elementary Particle Physics Seminar

The addition of salt into the heavy water (D2O) volume of the Sudbury Neutrino Observatory (SNO) has greatly increased the sensitivity to the neutral current (NC) neutrino interaction. A large part of the uncertainty on the charged current (CC) and NC flux measurements in the pure D2O phase was the correlation between NC and CC events. In the salt phase the Cherenkov light produced by the NC interaction is much more isotropic than for CC interactions. This has enhanced our ability to separate between the NC and CC interactions.

The SNO collaboration has to date published a neutrino spectrum for the CC neutrino interaction in the salt phase down to an electron energy of 5.5MeV (Phys. Rev. C 72, 055502 (2005)). This energy threshold was chosen to minimize the radioactive background contamination in the extracted neutrino signal. The CC energy spectrum above 5.5MeV shows little difference in shape between the undistorted 8B neutrino spectrum and the 8B spectrum distorted by the Large Mixing Angle (LMA) solution for neutrino oscillations. The LMA solution predicts an upturn in the CC spectrum at lower energies. By accounting for the internal and external radioactive backgrounds the CC energy spectrum was extracted down to an energy threshold of 4MeV.

The physics results from extracting the CC spectrum at lower energies are potentially very interesting. Not only does it offer a better test of the LMA solution, but allows for the test of potential "new physics". A lack of upturn in the CC spectrum below 5.5MeV for example could be explained by some sterile mixing theories or non-standard neutrino interactions.