The big questions in small systems

The early universe, very briefly after the Big Bang, was in a state of high temperature and high density. In order to recreate such a state of matter like the strongly coupled Quark–Gluon Plasma (sQGP) in the laboratory, mini bangs are produced by colliding heavy ions at the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory and subsequently at the Large Hadron Collider (LHC) at CERN. When the interesting results started pouring in from the LHC in high-energy p + p and p + A (small systems), the efforts to characterize the transition from these small systems to heavy ions (A + A) faced big questions, since the small system results have striking similarities to heavy ions in the higher multiplicity domains. The sQGP is a very good liquid with astonishingly low viscosity, and the recent observations of QGP-like phenomena in small collision systems have led to new implications. We briefly discuss these exciting new observations and their implications, including the questions that have emerged during such studies using heavy quarks. © (2023), (Indian Academy of Sciences). All Rights Reserved.