Search for quarks produced with large transverse momentum in 400-GeV proton-nucleus collisions

We have searched for charge-13 and charge-23 particles produced with large p in 400-GeV proton-Cu collisions. At p=6.15 GeV/c, 4.9 × 104 positive and 1.5 × 104 negative unit-charge particles provided the normalization; no fractionally charged particles were found. The 90%-confidence-level upper limits for the invariant production cross sections per nucleon for positive and negative charge-13 particles are 5.1 × 10-39 and 8.8 × 10-39 cm2 GeV-2, respectively; for charge-23 particles the respective limits are 1.3 × 10-39 and 2.2 × 10-39 cm2 GeV-2.