Abstract
Aspects and implications of the balance functions (BF) in high-energy physics are reviewed. The various calculations and measurements depending on different quantities, for example, system size, collisions centrality, and beam energy, are discussed. First, the different definitions including advantages and even short-comings are highlighted. It is found that BF, which are mainly presented in terms of relative rapidity, and relative azimuthal and invariant relative momentum, are sensitive to the interaction centrality but not to the beam energy and can be used in estimating the hadronization time and the hadron-quark phase transition. Furthermore, the quark chemistry can be determined. The chemical evolution of the new-state-of-matter, the quark-gluon plasma, and its temporal-spatial evolution, femtoscopy of two-particle correlations, are accessible. The production time of positive-negative pair of charges can be determined from the widths of BF. Due to the reduction in the diffusion time, narrowed widths refer to delayed hadronization. It is concluded that BF are powerful tools characterizing hadron-quark phase transition and estimating some essential properties.
Highlights
The quark-gluon plasma (QGP), a state of matter created at 0.1–1 μs after the Big Bang, is believed to be discovered in the relativistic heavy-ion collider (RHIC) at BNL, ten years ago [1,2,3,4,5]
The experimental features of NA22 [56] and STAR experiments [57] were essential to enable both of them analyzing the characteristics of balance functions (BF) [15, 28], which can be used as effective probes for the phase transition in heavy-ion collisions and e+ + e− collisions at intersecting storage rings (ISR) and PETRA energies [58]
The results presented in [28, 54] show that the string fragmentation implemented in PYTHIA describes the production particles and their charge balance functions
Summary
The quark-gluon plasma (QGP), a state of matter created at 0.1–1 μs after the Big Bang, is believed to be discovered in the relativistic heavy-ion collider (RHIC) at BNL, ten years ago [1,2,3,4,5]. The heavy-ion program at the large hadron collider (LHC) at CERN was designed to explore, among others, the properties of QGP In such sophisticated experimental facilities, the nucleus-nucleus collisions at ultrarelativistic energies are devoted to characterize the dynamical processes by which matter at extreme temperatures is produced and the fundamental properties that this matter exhibits. The balance functions (BF) were proposed by Bass et al [15] as a measure for the correlation of the positive and negative charged particles produced during the relativistic heavyion collisions Their width can be related to the hadronization time.
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