Stock continued such research from the mid-1980s with higher energies at CERN. He was a longtime spokesman for the NA49 experiment there. In a series of experiments started in 1994, the CERN scientists used the Super Proton Synchrotron (SPS) to create a quark–gluon plasma in relativistic collisions between lead nuclei and to indirectly detect the decay of the quark–gluon plasma into neutrons and protons. In a conference held in Turin in May 1999, the hundreds of CERN scientists from 22 countries reached a consensus that their combined results confirm the hypothesis that quarks become deconfined at high energy densities.