Abstract
The deuteron coalescence parameter B_2 in proton+proton and nucleus+nucleus collisions in the energy range of sqrt{s_{NN}}= 900–7000 GeV for proton + proton and sqrt{s_{NN}}= 2–2760 GeV for nucleus + nucleus collisions is analyzed with the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model, supplemented by an event-by-event phase space coalescence model for deuteron and anti-deuteron production. The results are compared to data by the E866, E877, PHENIX, STAR and ALICE experiments. The B_2 values are calculated from the final spectra of protons and deuterons. At lower energies, sqrt{s_{NN}}le 20 GeV, B_2 drops drastically with increasing energy. The calculations confirm that this is due to the increasing freeze-out volume reflected in B_2sim 1/V. At higher energies, sqrt{s_{NN}}ge 20 GeV, B_2 saturates at a constant level. This qualitative change and the vanishing of the volume suppression is shown to be due to the development of strong radial flow with increasing energy. The flow leads to strong space-momentum correlations which counteract the volume effect.
Highlights
The exploration of the theory of strong interaction, called Quantum Chromodynamics (QCD), is one of the major goals of today’s high energy physics
As a first step to classify the production process, this paper investigates the formation of deuterons by the phase space coalescence of protons and neutrons
The proton spectra can be tuned to the data using the Perugia SOFT tune [40] with CTEQ 5M1. This tune will be implemented in the version of Ultrarelativistic Quantum Molecular Dynamics (UrQMD)
Summary
The exploration of the theory of strong interaction, called Quantum Chromodynamics (QCD), is one of the major goals of today’s high energy physics. QCD is a non-abelian gauge theory that predicts a transition of the known hadronic matter seen in nuclei at ground-state density to a fluid-like state called the Quark-Gluon-Plasma, QGP. This transition may either happen if a critical temperature around 150–160 MeV is reached or if a critical baryon density, around 4-5 times the ground state density, is created [1]. The study of cluster formation processes in heavy ion collisions is of particular interest for a multitude of reasons: Firstly, clusters probe the two-particle baryon correlations in phase space, i.e. they allow to explore the space and momentum space structure of the emission source [2]. The probability of creating Nd deuterons in a certain momentum space volume after freeze-out is proportional to the number of produced neutrons Nn and protons N p (which can be further simplified, if one assumes the same number of protons and neutrons) [16]:
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