Abstract
The dynamics of baryon-antibaryon annihilation and reproduction ($B{\bar B} \leftrightarrow 3 M$) is studied within the Parton-Hadron-String Dynamics (PHSD) transport approach for Pb+Pb and Au+Au collisions as a function of centrality from lower Super Proton Synchrotron (SPS) up to Large Hadron Collider (LHC) energies on the basis of the quark rearrangement model (QRM). At Relativistic Heavy-Ion Collider (RHIC) energies we find a small net reduction of baryon-antibaryon ($B {\bar B}$) pairs while for the LHC energy of $\sqrt{s_{NN}}$ = 2.76 GeV a small net enhancement is found relative to calculations without annihilation (and reproduction) channels. Accordingly, the sizeable difference between data and statistical calculations in Pb+Pb collisions at $\sqrt{s_{NN}}$= 2.76 TeV for proton and antiproton yields \cite{53}, where a deviation of 2.7 $\sigma$ was claimed by the ALICE Collaboration, should not be attributed to a net antiproton annihilation. This is in line with the observation that no substantial deviation between the data and statistical hadronization model (SHM) calculations is seen for antihyperons, since according to the PHSD analysis the antihyperons should be modified by the same amount as antiprotons. As the PHSD results for particle ratios are in line with the ALICE data (within error bars) this might point towards a deviation from statistical equilibrium in the hadronization (at least for protons/antiprotons). Furthermore, we find that the $B {\bar B} \leftrightarrow 3 M$ reactions are more effective at lower SPS energies where a net suppression for antiprotons and antihyperons up to a factor of 2 -- 2.5 can be extracted from the PHSD calculations for central Au+Au collisions.
Highlights
Relativistic and ultrarelativistic heavy-ion collisions offer the unique possibility to study a new phase of matter, i.e., a quark-gluon plasma (QGP), as well as possibly the phase boundary between the hadronic and partonic phase
Evolution of the protons is very similar to that of the antiprotons in all scenarios considered. This is essentially due to the fact that at this energy the baryon chemical potential is approximately zero and particle-antiparticle reactions are treated on the same footing in Hadron-String Dynamics (HSD) and Parton-HadronString Dynamics (PHSD)
At top Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energies these modifications are below the 20% level since baryon and antibaryon densities are comparable and all elastic and inelastic 2 ↔ 2 channels are equal for time reversed states
Summary
Relativistic and ultrarelativistic heavy-ion collisions offer the unique possibility to study a new phase of matter, i.e., a quark-gluon plasma (QGP), as well as possibly the phase boundary between the hadronic and partonic phase. Molecular Dynamics (UrQMD) transport model [22,23] has been employed as an hadronic “afterburner” to evaluate the final-state interactions and in particular the effects from BBannihilation after chemical freezeout; the backward channels had been discarded violating detailed balance [24]. This issue has been further addressed in Ref.
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