Strongly Interacting Quark Gluon Plasma Discovered at RHIC

Abstract

Quarks and gluons, fundamental fermions and bosons in strong interaction, are confined inside hadrons and are not observed as isolated entities in the present universe. Early universe within several micro-seconds after its birth was ultra-hot and was in the form of the quark-gluon plasma (QGP), with quarks and gluons freed from confinement. Studies aiming at realizing QGP and investigating its properties in laboratories have been performed using heavy-ion accelerators. From the investigations of last ten years at RHIC, it has been found that QGP is not a gaseous object where quarks and gluons are freely moving around, but a fluid state with the smallest specific shear viscosity in the world, whose origin is ascribed to their mutual interaction with the highest strength in the world. In this article, we will describe plainly how properties of QGP have been revealed.