High energy heavy ion collisions. Measured quantities and their interpretations

The relativistic heavy ion collisions are the only means to experimentally study the plasma states of Quantum Chromodynamics (QCD) in which the degree of freedom of quarks and gluons becomes obvious. The physical meanings of the experimentally observed values at high energy heavy ion colliders represented by the relativistic heavy ion collider RHIC at BNL are reported briefly on the basis of their recent research outcomes. The paper consists of the following sections and subsections. 1) Introduction, 2) Relativistic Heavy Ion Collisions; 2.1. Space-time evolution picture, 2.2. Variables characterizing collision events, 3) Collective features; 3.1. Chemical freeze-out and statistical models, 3.2. Kinetic freeze-out and radial flow, 3.3 Elliptic flow, 3.4. Perfect fluid? 4) High Momentum Hadron Suppression and Energy Loss Evaluation; 4.1. Energy loss in media, 4.2. Suppression of high transverse momentum distribution, 4.3. Azimuthal two-particle correlation, 5) Suppression of J/ψ Generation, 6) Quark Number Scaling, and 7) Summaries. (S. Funahashi)