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The parton to hadron phase transition observed in Pb + Pb collisions at 158 GeV per nucleon
| Content Provider | Semantic Scholar |
|---|---|
| Author | Stock, Reinhard |
| Copyright Year | 1999 |
| Abstract | Hadronic yields and yield ratios observed in Pb+Pb collisions at the SPS energy of 158 GeV per nucleon are known to resemble a thermal equilibrium population at T = 180 ± 10 M eV , also observed in elementary e + + e − to hadron data at LEP. We argue that this is the universal consequence of the QCD parton to hadron phase transition populating the maximum entropy state. This state is shown to survive the hadronic rescattering and expansion phase, freezing in right after hadronization due to the very rapid longitudinal and transverse expansion that is inferred from Bose-Einstein pion correlation analysis of central Pb+Pb collisions. Recent Lattice-QCD theory predicts the disappearance of the hadronic phase of matter once the energy density exceeds a critical value of about 1 to 1.5 GeV per f m 3 [1], giving rise to a continuous, partially deconfined QCD state that is governed by the elementary interaction of quarks and gluons. To recreate this phase in the laboratory one collides heavy nuclei at relativistic energy, with the goal of ascertaining the QCD predictions, and to pin down the decay point from the partonic to the hadronic phase by obtaining estimates for the transition temperature and energy density. The CERN SPS Lead (208 P b) beam facility provides for a top energy of 158 GeV per projectile nucleon, corresponding to a total internal CM-system energy of about 3.5 T eV , to heat and compress the primordial reaction volume. In fact calorimetric data [2] show that the average transverse energy density exceeds about 2.5 GeV /f m 3 in that volume, in central P b + P b collisions. Moreover the study of J/Ψ production [3] demonstrates a suppression of the yield in such collisions, characteristic of the QCD " Debeye " screening mechanism expected in a deconfined partonic medium [4]. If one tentatively takes for granted such indications of a deconfined state at top SPS energy one expects, likewise, to receive signals specific to the bulk parton to hadron phase transformation bound to occur once the primordial high density state expands and cools toward the critical temperature and energy density. In the present letter we shall examine the proposal [5, 6, 7, 8] that such a signal is indeed provided for by the composition of the bulk hadron final state, in terms of the yields and yield ratios of the various mesonic … |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://arxiv.org/pdf/hep-ph/9905247v1.pdf |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | Cardiomyopathies Compresses (device) Density matrix Emoticon Estimated Freezing IBM 1401 Symbolic Programming System Inference Lattice QCD Lead Nucleons Phase Transition Population Transverse wave Zero suppression collision paclitaxel liposome |
| Content Type | Text |
| Resource Type | Article |
