Mixed states for neutral current neutrino oscillation.

The theory of neutrino oscillation predicts that if both neutrino and antineutrino coming from Z 0 decay are detected, one can observe an oscillation pattern between the corresponding detectors. This prediction is based on two properties; the neutrino-antineutrino pairs are produced coherently and they are detected with definite flavor in detectors. In this paper, we reanalyze this problem with considering some massive neutrinos which are mixed with the light neutrinos but they either participate incoherently or are decoupled in the production and detection processes. In fact, neutrinos whose masses are larger than the upper bound on the mass uncertainty to be compatible with the coherence conditions (we will see it is about 1 keV) must be treated incoherently. Very heavy neutrinos whose masses are much larger than the neutrino energy in the neutrino production process are decoupled. Under these conditions, the created neutrino-antineutrino state as well as the states of detected neutrino and antineutrino is mixed. We see that the oscillation pattern cannot be observed for incoherent neutrinos and the standard oscillation pattern is recovered if the light neutrino masses are ignored in the production and detection processes. Moreover, since the Z 0 decay process is performed blindly with respect to flavors, the oscillating contributions in the event rates are independent of the Z 0 decay width. [ABSTRACT FROM AUTHOR]