A Search For Free Quarks In Heavy-Ion Collisions At 60 And 200 Gev/Nucleon

We have carried out a search for quarks produced by the heavy ions at the CERN SPS. A mercury target exposed to the oxygen and sulfur beams was concentrated by distillation. The residue was tested using a modified Millikan apparatus. No fractional charges were observed. We set upper limits on quark production of about 10−7 quarks per beam-particle interaction, or about 10−6 quarks per central collision.