 The neutrino accounted for the missing energy , but Fermi 's theory described a particle with little mass and no electric charge that would be difficult to observe directly . In a 1934 paper , Rudolf <unk> and Hans Bethe calculated that neutrinos could easily pass through the Earth , and concluded " there is no practically possible way of observing the neutrino . " In 1951 , at the conclusion of the Greenhouse test series , Reines received permission from the head of T Division , J. Carson Mark , for a leave in residence to study fundamental physics . Reines and his colleague Clyde Cowan decided to see if they could detect neutrinos . " So why did we want to detect the free neutrino ? " he later explained , " Because everybody said , you couldn ’ t do it . " 
