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Sonja Kabana

Publications and source records attributed to Sonja Kabana.

10 recordsLinked to original sources
arXiv2011

Probing the QGP Phase Boundary with Thermal Properties of $ϕ$ Mesons

A novel attempt has been made to probe the QCD phase boundary by using the experimental data for transverse momenta of ϕ mesons produced in nuclear collisions at AGS, SPS and RHIC energies. The data are confronted with simple thermodynamic expectations and lattice QCD results. The experimental data indicate a first-order phase transition, with a mixed phase stretching the energy density between \sim1 and 3.2 GeV/fm3 corresponding to SPS energies.

nucl-ex↗
arXiv2002

Stable quark stars beyond neutran stars : can they account for the missing matter ?

The structure of a spherically symmetric stable dark 'star' is discussed, at zero temperature, containing 1) a core of quarks in the deconfined phase and antileptons 2) a shell of hadrons in particular $n$, $p$, $Λ$ and $Σ^-$ and leptons or antileptons and 3) a shell of hydrogen in the superfluid phase. If the superfluid hydrogen phase goes over into the electromagnetic plasma phase at densities well below one atom / $(10 fm)^{3}$, as is usually assumed, the hydrogen shell is insignificant for the mass and the radius of the 'star'. These quantities are then determined approximatively : mass = 1.8 solar masses and radius = 9.2 km. On the contrary if densities of the order of one atom / $(10 fm)^{3}$ do form a stable hydrogen superfluid phase, we find a large range of possible masses from 1.8 to 375 solar masses. The radii vary accordingly from 9 to 1200 km.

hep-ph↗
arXiv2001

A new interpretation of the QCD phase transition and of strangeness as QGP signature

We address the question of how to identify the QCD phase transition using measured light (u,d,s-structured) hadrons, without invoking comparison to the QCD $ε_c$ predictions, and extract $ε_c$ from the data. We analyse several particle and nuclear collisions and extract their chemical freeze-out temperature $T$ at zero baryochemical potential ($μ_B$). We find at $μ_B=0$ a universal rise and saturation of both the $T$ and of the strangeness suppression factor $λ_s$ (=$\frac {2\bar{s}} {\bar{u} + \bar{d}} $) with increasing initial energy density ($ε_i$). The onset of saturation of both $T$ and $λ_s$, is interpreted as due to the event of the QCD phase transition. The critical energy density is estimated to be $ε_c$ $\sim$ 1 +0.3 -0.5 GeV/fm$^3$, corresponding approximately to a $\sqrt{s}$ of $\sim$ 8.8 GeV for central Pb+Pb collisions. Concerning the role of strangeness, we identify trivial and non-trivial sources of strangeness enhancement: The peak of $λ_s$ in Pb+Pb collisions at $\sqrt{s}$=8.8 GeV and other phenomena of 'strangeness enhancement' defined with respect to p+p data, are trivially traced back to the different baryochemical potentials and $ε_i$ of the compared systems. A non trivial redefined '$λ_s$ enhancement' is however also present. The netbaryonfree $λ_s$ limit is estimated to be approximately reached in Au+Au collisions at the LHC.

hep-ph↗
arXiv2001

A (re)interpretation of the QCD phase transition and of strangeness as QGP signature

The temperature at the chemical freeze-out and at zero baryochemical potential has been extracted in a global analysis of $e^+e^-$, $p+p$, $p+ \overline{p}$ and $A+A$ collisions at $\sqrt{s}$=2-1800 GeV per N+N pair. We demonstrate that the temperature at $μ_B$=0, rises with the initial energy density $ε_i$, and saturates above $ε_i$ $\sim$ 1 GeV/fm$^3$. This behaviour is interpreted as mapping out the QCD phase transition universally in particle and nuclear collisions. The critical energy density is therefore identified to be $ε_{crit}$ $\sim$ 1 $\pm$ 0.3 GeV/fm$^3$. We show that strange particles at $μ_B$=0, are not significantly enhanced in A+A collisions as compared to $p+ \overline{p}$. The so called 'strangeness suppression factor' ($λ_s = \frac{(2 \overline{s})} {(\overline{u} + \overline{d})}$) as a function of $ε_i$ is following the temperature, rising and saturating universally above $ε_{crit}$. This leads to a reinterpretation of strangeness enhancement as QGP signature. Within this interpretation the experimental puzzles with respect to strangeness production can be naturally explained: e.g. the recent measured maximum of $K^+/π^+$ in Pb+Pb collisions at 40 A GeV, is explained as due to $μ_B$. We discuss under which conditions 'strangeness enhancement' and '$J/Ψ$ suppresion' both set in at $ε_{crit}$ $\sim$ 1 GeV/fm$^3$.

hep-ph↗
arXiv2001

The strange border of the QCD phases

We address the flavour composition along the border between the hadronic and the quark-gluon plasma phases of QCD. The ratio of strange to up and down antiquarks ($λ_s$) produced in partic le and nuclear collisions, is found to increase in collisions with initially reached energy density ($ε_i$) up to $ε_{crit}$ $\sim$ 1 GeV/$fm^3$. Above this value it decreases approximately linearly and reaches its asymptotic value at zero baryon chemical potential ($μ_B$). We demonstrate that $λ_s$ in nuclear collisions is approaching its asymptotic value at $ε_i$ $\sim$ 8-9 GeV/$fm^3$, corresponding to $\sqrt{s}$ $\sim$ 3-8 TeV per nucleon+nucleon pair which will be reached at the LHC. After correcting for the difference in the chemical potentials of various colliding systems, $λ_s$ universally saturates across the QCD phase boundary, following the temperature. Recent experimental puzzles as the increase in the $K/π$ ratio in Pb+Pb collisions at 40 GeV per nucleon, its different behaviour at midrapidity, the decrease of the double ratio of $K/π$(A+A/p+p) in nucleus nucleus over p+p collisions with increasing $\sqrt{s}$, and the increase of $λ_s$ in p+A over p+p collisions at the same $\sqrt{s}$, are naturally explained. We study the approach of thermodynamic observables at $μ_B=0$ to the transition point and extract an estimate of the critical temperature.

hep-ph↗
arXiv2000

Hadronic centrality dependence in nuclear collisions

The kaon number density in nucleus+nucleus and p+p reactions is investigated for the first time as a function of the initial energy density $ε$ and is found to exhibit a discontinuity around $ε$=1.3 GeV/fm$^3$. This suggests a higher degree of chemical equilibrium for $ε>$ 1.3 GeV/fm$^3$. It can also be interpreted as reflection of the same discontinuity, appearing in the chemical freeze out temperature (T) as a function of $ε$. The $N^{α\sim 1}$ dependence of (u,d,s) hadrons, with N the number of participating nucleons, also indicates a high degree of chemical equilibrium and T saturation, reached at $ε>$1.3 GeV/fm$^3$.Assuming that the intermediate mass region (IMR) dimuon enhancement seen by NA50 is due to open charm ($D \bar{D}$), the following observation can be made: a) Charm is not equilibrated. b) $J/Ψ/D \bar{D}$ suppression -unlike $J/Ψ/DY$- appears also in S+A collisions, above $ε$ $\sim$1 GeV/fm$^3$. c) Both charm and strangeness show a discontinuity near the same $ε$. d) $J/Ψ$ could be formed mainly through $c \bar{c}$ coalescence. e) The enhancement factors of hadrons with u,d,s,c quarks may be connected in a simple way to the mass gain of these particles if they are produced out of a quark gluon plasma (QGP). We discuss these results as possible evidence for the QCD phase transition occuring near $ε\sim $1.3 GeV/fm$^3$.

hep-ph↗
arXiv2000

Mapping out the QCD phase transition in multiparticle production

We analyze multiparticle production in a thermal framework for 7 central nucleus nucleus collisions, $e^+$+ $e^-$ annihilation into hadrons on the Z resonance and 4 hadronic reactions (p+p and p+$\bar{p}$ with partial centrality selec tion), with center of mass energies ranging from $\sqrt{s}$= 2.6 GeV (per nucleon pair) to 1.8 TeV. Thermodynamic parameters at chemical freeze-out (temperature and baryon and strangeness fugacities) are obtained from appropriate fits, generally improving in quality for reactions subjected to centrality cuts. All systems with nonvanishing fugacities are extrapolated along trajectories of equal energy density, density and entropy density to zero fugacities. The so obtained temperatures extrapolated to zero fugacities as a function of initial energy density $ε_{in}$ universally show a strong rise followed by a saturating limit of $T_{lim}$ = 155 $\pm$ 6 $\pm$ 20 MeV. We interpret this behaviour as mapping out the boundary between quark gluon plasma and hadronic phases. The ratio of strange antiquarks to light ones as a function of the initial energy density $ε_{in}$ shows the same behaviour as the temperature, saturating at a value of 0.365 $\pm$ 0.033 $\pm$ 0.07. No distinctive feature of 'strangeness enhancement' is seen for heavy ion collisions relative to hadronic and leptonic reactions, when compared at the same initial energy density.

hep-ph↗
arXiv2000

Hadronic centrality dependence in nuclear collisions

The kaon number density in nucleus+nucleus and p+p reactions is investigated for the first time as a function of the initial energy density $ε$ and is found to exhibit a discontinuity around $ε$=1.3 GeV/fm$^3$. This suggests a higher degree of chemical equilibrium for $ε>$ 1.3 GeV/fm$^3$. It can also be interpreted as reflection of the same discontinuity, appearing in the chemical freeze out temperature (T) as a function of $ε$. The $N^{α\sim 1}$ dependence of (u,d,s) hadrons, whith N the number of participating nucleons, also indicates a high degree of chemical equilibrium and T saturation, reached at $ε>$1.3 GeV/fm$^3$. Assuming that the intermediate mass region (IMR) dimuon enhancement seen by NA50 is due to open charm ($D \bar{D}$), the following observation can be made: a) Charm is not equilibrated. b) $J/Ψ/D \bar{D}$ suppression -unlike $J/Ψ/DY$- appears also in S+A collisions, above $ε$ $\sim$1 GeV/fm$^3$. c) Both charm and strangeness show a discontinuity near the same $ε$. d) $J/Ψ$ could be formed mainly through $c \bar{c}$ coalescence. e) The enhancement factors of hadrons with u,d,s,c quarks may be connected in a simple way to the mass gain of these particles if they are produced out of a quark gluon plasma (QGP). We discuss these results as possible evidence for the QCD phase transition occuring near $ε\sim $1.3 GeV/fm$^3$.

hep-ph↗
arXiv2000

Charm in nuclear reactions in sqrt(s)=17 and 19 GeV

Consequences resulting from the D Dbar excess derived indirectly by the NA50 experiment in S+U and Pb+Pb collisions at sqrt(s)=19, 17 GeV, relevant for the identification of the QCD phase transition in these collisions, are discussed. The dependence of open and closed charm yields in Pb+Pb collisions on the number of participating nucleons (N) indicates non thermal charm production and J/Psi dissociation, stronger than the absorption seen in any other elementary hadron. The J/Psi in central Pb+Pb collisions could originate dominantly from c cbar pair coalescence out of a hadronizing quark and gluon environment. Furthermore, the J/Psi appears to be suppressed in S+U collisions at sqrt(s)=19 GeV, as opposed to current interpretations. A significant change in the (J/Psi)/D Dbar ratio as well as in the number density of kaons is observed above energy density approx. 1 GeV/fm^3, suggesting a change of phase at this energy density, and underlining the importance of direct open charm measurements.

hep-ph↗