Investigating the Emergence of Collective Phenomena in Hadronic Collisions

In 2005 scientists working at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) discovered that the quark-gluon plasma (QGP) formed in the collisions of nuclei moving at nearly the speed of light flows as a nearly perfect liquid. While the QGP has the highest temperatures and densities ever studied in the laboratory, it nonetheless flows with less internal friction than any other fluid. In 2009, experiments at the Large Hadron Collider (LHC) in Switzerland demonstrated that the QGP also strongly modifies “jets”, the collimated sprays of particle that emerge when the highest energy quarks and gluons scatter off each other. More recently, further work, first at the LHC and then at RHIC, showed that the “nearly perfect liquid” flow pattern persists in the smallest collision systems studied, both in the collisions of a proton with a nucleus and even in proton+proton collisions. The research program proposed here will probe the QGP liquid with jets at the smallest length scales, using ATLAS, an existing large experiment at the LHC and later a complementary experiment sPHENIX being constructed at RHIC. By doing so, we intend to link the microscopic structure of the QGP at small length scales to its emergent liquid properties observed at 10-100 times longer length scales.