The NJL model and strange quark matter

The stability of strange quark matter is studied within the Nambu Jona-Lasinio model with three different parameter sets. The model Lagrangian contains 4-fermion (with and without vector interaction) and 6-fermion terms; the minimum energy per baryon number as a function of the strangeness fraction of the system is compared to the masses of hyperons having the same strangeness fraction, and coherently calculated in the same version of the model, and for the same parameter set. The results show that in none of the different parameter sets strangelets are stable, and in some cases a minimum in the energy per baryon does not even exist.Comment: 8 pages, 2 figures, reference added, typos corrected, version to appear in Europhys. Let

Flack

Fiction by Emilio P. Ratti

Lattice QCD-based equations of state at vanishing net-baryon density

We present realistic equations of state for QCD matter at vanishing net-baryon density which embed recent lattice QCD results at high temperatures combined with a hadron resonance gas model in the low-temperature, confined phase. In the latter, we allow an implementation of partial chemical equilibrium, in which particle ratios are fixed at the chemical freeze-out, so that a description closer to the experimental situation is possible. Given the present uncertainty in the determination of the chemical freeze-out temperature from first-principle lattice QCD calculations, we consider different values within the expected range. The corresponding equations of state can be applied in the hydrodynamic modeling of relativistic heavy-ion collisions at the LHC and at the highest RHIC beam energies. Suitable parametrizations of our results as functions of the energy density are also provided.Comment: Updated journal version with refined EoS-parametrization. July 2014. 8 pp. 4 figs. 3 parametrization-tables and weblink Ref. [45

Are there hadronic bound states above the QCD transition temperature?

Recent lattice QCD calculations, at physical pion masses and small lattice spacings that approach the continuum limit, have revealed that non-diagonal quark correlators above the critical temperature are finite up to about 2 $T_c$. Since the transition from hadronic to free partonic degrees of freedom is merely an analytic cross-over, it is likely that, in the temperature regime between 1-2 $T_c$, quark and gluon quasiparticles and pre-hadronic bound states can coexist. The correlator values, in comparison to PNJL model calculations beyond mean-field, indicate that at least part of the mixed phase resides in color-neutral bound states. A similar effect was postulated for the in-medium fragmentation process, i.e. for partons which do not thermalize with the system and thus constitute the non-equilibrium component of the particle emission spectrum from a deconfined plasma phase. Here, for the first time we investigate the likelihood of forming bound states also in the equilibrated, parton dominated phase above $T_c$ which is described by lattice QCD.Comment: 15 pages, 4 Figure

Multigap RPC time resolution to 511 keV annihilation photons

The time resolution of Multigap Resistive Plate Counters (MRPCs) to $511$ keV gamma rays has been investigated using a $^{22}$Na source and four detectors. The MRPCs time resolution has been derived from the Time-of-Flight information, measured from pairs of space correlated triggered events. A GEANT4 simulation has been performed to analyze possible setup contributions and to support experimental results. A time resolution (FWHM) of $376$ ps and $312$ ps has been measured for a single MRPC with four $250$ $\mu$m gas gaps by considering respectively one and two independent pairs of detectors.Comment: 25 pages, 14 figure

Propuesta de una metodología estándar para la caracterización de la organogelificación de aceites comestibles con ceras

Saturated and trans fatty acids play a significant role in the plastic properties of food. However, health recommendations suggest limiting their intake. One approach which got the attention of researchers was to decrease the amount of saturated and trans fatty acids in food by the structuring of edible oils through the crystallization of waxes. The underlying mechanisms that lead to organogelation and the properties that characterize well-structured edible oil have been slow to fully understand due in part to a lack of standardiza­tion in their analysis which often makes the comparison between research results from different laboratories difficult. The aim of this work was to review previously reported methods for the characterization of organo­gelation using vegetable and animal waxes, and to propose a minimal standardization for an organogelation analysis.Los ácidos grasos saturados y trans juegan un rol significativo en las propiedades plásticas de los alimentos. Sin embargo, las recomendaciones de salud sugieren limitar su consumo. Un enfoque que han propuesto investigadores científicos es la disminución en la cantidad de grasas trans y saturadas en la alimenta­ción por medio de la estructuración de aceites comestibles a partir de la cristalización de ceras. Los mecanismos por los cuales la organogelificación ocurre, así como las propiedades que caracterizan una buena estructuración del aceite, han sido descubiertos lentamente debido en parte a la falta de estandarización de los análisis impli­cados, lo que frecuentemente vuelve difícil la comparación entre resultados de investigación de distintos labo­ratorios. El objetivo de este trabajo es realizar una revisión de los principales métodos para la caracterización de la organogelificación y de los organogeles formados usando ceras vegetales y animales, proponiendo una estandarización mínima del análisis de organogelificación