Speaker
Description
Hadron yields obtained from elementary collisions up to heavy-ions
have been successfully described by
thermal models with a few parameters such as temperature and baryon
chemical potential [1, 2].
However, the LHC$/$ALICE experiment has recently found that the proton
and antiproton yields are a factor of 2 too low compared to thermal
description [3]. This has been shown to arise from
baryon-antibaryon ($B\bar{B}$) annihilations which can still be
appreciable after chemical freeze-out because
of their large cross-sections while the reverse reactions of
multi-particles fusing into a $B\bar{B}$ pair cannot be sustained [4]. In this study, we include the $B\bar{B}$ annihilation effect
into the thermal model [5] by introducing one more parameter for
the out-of-equilibrium annihilation loss of the protons. We use the quark model description for the annihilation losses of the other (anti-)baryons. We assume
annihilation of a $B\bar{B}$ pair produces a certain number of mesons
(default 5 pions and kaons depending on the strangeness
content) [4, 6]. We fit both heavy-ion data ($\sqrt{s}_{\rm NN} = $ 6.27 GeV to 2.76 TeV) and proton-proton collision data ($\sqrt{s}_{\rm NN} = $ 200, 900, and 7000 GeV) at SPS, RHIC and LHC energies. We obtain new chemical freeze-out parameters with significantly improved fit quality in comparison to the default thermal model.
We find that the baryon loss increases with increasing collision
energy while the antibaryon loss decreases. We further find a significant increase in the chemical freeze-out temperature compared to the default
fit, potentially provoking a rethink of the nuclear phase diagram.
References
[1] P. Braun-Munzinger et al., Phys. Lett. B, 365, 1 (1996).
[2] J. Cleymans and K. Redlich, Phys. Rev. C 60, 054908 (1999); J. Cleymans et al., Phys. Rev. C 79, 014901 (2009).
[3] B. Abelev et al. (ALICE Collaboration), Phys. Rev. Lett. 109, 252301
(2012); J. Stachel et al. Nucl. Phys. A 904, 535 (2013).
[4] J. Steinheimer {\it et al.} Phys. Rev. Lett, 110, 042501 (2013); F. Becattini {\it et al.}, Phys. Rev. Lett 111, 082302 (2013).
[5] S. Wheaton and J. Cleymans, Comput. Phys. Commun. 180, 84 (2009).
[6] Yinghua Pan and Scott Pratt, arXiv:1210.1577.
| Preferred Track | Baryon-Rich QCD Matter and Astrophysics |
|---|---|
| Collaboration | Not applicable |
