The following event is an example of a cosmic ray interaction in the NuTeV detector:
Cosmic rays are particles that bombard the earth from anywhere beyond the earth's atmosphere. They originate either from outside the solar system or are associated with energetic solar events (for example, solar flares). They appears as soft showering particles that enter the NuTeV detector vertically and typically leave short tracks. They are also usually low energy events (see EHDNC value recorded at the top right).
Since cosmic rays are arriving at all times, such interactions can occur while we are taking neutrino data.