Most physicists and astrophysicists believe that space, time, and all the matter and radiation in the Universe were formed during the big-bang some 15 billion years ago. A key challenge is to understand how the Universe we live in today evolved from the cosmic fireball created in the big-bang.
As our understanding of the laws of physics improves, we are able to look further back in time, and unravel the structure of the early Universe and its subsequent evolution. It is widely believed that almost equal amounts of matter and antimatter were created in the big-bang, and that most of the antimatter, if not all of it, annihilated on matter after the Universe had cooled and expanded. This annihilation, which started about 20 μs after the big-bang, occurred after most of the matter we see in the Universe today was already in the form of neutrons, protons, and other hadrons made of quarks. Before the Universe hadronized, it existed in a phase of quarks and gluons in which the matter–antimatter asymmetry which makes the Universe around us today had been a small and insignificant aberration.
We are attempting to recreate this phase today, and to study it in the laboratory. This primordial state of hadronic matter called quark–gluon plasma (QGP) for all purposes an inescapable consequence of our current knowledge about the fundamental hadronic interactions, which is qualitatively rooted in the SU (3)-gauge theory, quantum chromodynamics (QCD). We are seeking to verify this prediction and to understand this novel form of matter. To accomplish this, we ‘squeeze’ the normal nuclear matter in relativistic nuclear collisions at sufficiently high energy. The individual nucleons dissolve, and we hope and expect that their constituents will form the sought-after state, the (color-charged) plasma of freely moving deconfined quarks and gluons.
What are the interesting physical phenomena which can be explored by high-energy nucleus-nucleus collisions ?
This is the most important question in the high-energy physics community. To answer this question, it is useful to note that one of the most important characteristics of high energy nucleus-nucleus is the large amount of energy involved and interestingly when a large fraction of this energy is deposited in a small region of space in a short duration of time. In this region, the energy density is therefore very large. An energy density of the order of a few GeV/fm3. This energy density of nuclear matter in equilibrium, may favor the formation of new forms of matter such as the quark-gluon plasma. The search fro new forms of matter under extreme conditions of high energy densities and high temparatures is an important objective of high-energy heavy-ion collisions.
We are attempting to recreate this phase today, and to study it in the laboratory. This primordial state of hadronic matter called quark–gluon plasma (QGP) for all purposes an inescapable consequence of our current knowledge about the fundamental hadronic interactions, which is qualitatively rooted in the SU (3)-gauge theory, quantum chromodynamics (QCD). We are seeking to verify this prediction and to understand this novel form of matter. To accomplish this, we ‘squeeze’ the normal nuclear matter in relativistic nuclear collisions at sufficiently high energy. The individual nucleons dissolve, and we hope and expect that their constituents will form the sought-after state, the (color-charged) plasma of freely moving deconfined quarks and gluons.
What are the interesting physical phenomena which can be explored by high-energy nucleus-nucleus collisions ?
This is the most important question in the high-energy physics community. To answer this question, it is useful to note that one of the most important characteristics of high energy nucleus-nucleus is the large amount of energy involved and interestingly when a large fraction of this energy is deposited in a small region of space in a short duration of time. In this region, the energy density is therefore very large. An energy density of the order of a few GeV/fm3. This energy density of nuclear matter in equilibrium, may favor the formation of new forms of matter such as the quark-gluon plasma. The search fro new forms of matter under extreme conditions of high energy densities and high temparatures is an important objective of high-energy heavy-ion collisions.
