Search for massive long-lived particles in aluminum targets irradiated by 300- and 400-GeV protons

We have used a directional gas Cherenkov counter, which employed six phototubes to sample Cherenkov light from single particles having a $\gamma [\equiv {(1-\frac{v^2}{c^2})}^{-\frac{1}{2}}]$ greater than ∼ 10, to achieve accidental rates of less than one per day if operated near targets with surface radiation levels of as high as 10⁺³ R/h. The cosmic-ray background measured by our apparatus was reduced to less than one per day by mounting our directional Cherenkov counter above the irradiated targets and facing toward the earth. Two searches of a few days' duration, after bombardments at energies of 300 and 400 GeV with > 10¹⁶ protons at NAL, were made in 4-in.-thick targets of aluminum mounted just downstream from another aluminum target. No long-lived particles were observed with cross sections for production and capture of approximately less than a picobarn in a lifetime range of a few to a few thousand hours.