Small system studies: A theory overview

Understand

There is now a substantial body of evidence that a deconfined quark-gluon plasma is created in ultrarelativistic collisions of heavy nuclei.

• Some key observables which are used to gauge the production of the quark-gluon plasma are the hadronic spectra and multiplicities across many species, azimuthal anisotropies in the production of various hadrons, jet quenching, photon/dilepton production, and heavy quarkonium suppression.
• A key question in the study of the quark-gluon plasma is what happens to these observables as one changes the system size.
• In particular, it is very interesting to study collisions of `small systems' such as pp, dA, pA, and $e^+ e^-$ since naively one does not expect to produce a QGP in these cases.