Search for Ultradense Nuclei in Relativistic Collisions of Ar on Pb

Abstract

In 2.5\ifmmode\times\else\texttimes\fi{}${10}^{8}$ interactions of 1.1- to 1.6-GeV/nucleon $^{40}\mathrm{Ar}$ ions with a Pb target we saw no tracks of products with $Z>20$ ejected in the beam direction, using a Lexan detector stack. The upper limit on the formation cross section is about 50 nb for products with $26\ensuremath{\lesssim}Z\ensuremath{\lesssim}40$ and increases with $Z$ to about 1.5 \ensuremath{\mu} b for $Z=100$.