Quarks with unit charge: a search for anomalous hydrogen. [Upper limits, mass dependence, cross sections]
R. A. Muller, Luis W. Alvarez, William R. Holley, E.J. Stephenson · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1977
Quarks of charge +1 and other anomalous hydrogen were sought by using the 88-inch cyclotron at Berkeley as a high-energy mass spectrometer, with natural hydrogen and deuterium as the sources of ions. No quarks were observed, and limits were placed on their ratio to protons on the earth that vary from less than 2 x 10/sup -19/ for high masses (3 to 8.2 atomic mass units) to 10/sup -13/ for the lowest masses (less than 1/3 atomic mass unit).