Altas Energias

M. Broilo, E. G. S. Luna, and M. J. Menon

Phys. Rev. D 98, 074006 – Published 5 October 2018

ABSTRACT

Recent data from LHC13 by the TOTEM Collaboration indicate an unexpected decrease in the value of the ρ parameter and a σtot value in agreement with the trend of previous measurements at 7 and 8 TeV. These data at 13 TeV are not simultaneously described by the predictions from Pomeron models selected by the COMPETE Collaboration but show agreement with the maximal Odderon dominance, as recently demonstrated by Martynov and Nicolescu. Here, we present a detailed analysis on the applicability of Pomeron dominance by means of a general class of forward scattering amplitude, consisting of even-under-crossing leading contributions associated with single, double, and triple poles in the complex angular momentum plane and subleading even and odd Regge contributions. The analytic connection between σtot and ρ is obtained by means of singly subtracted dispersion relations, and we carry out fits to pp and ¯pp data in the interval 5 GeV–13 TeV. The data set comprises all the accelerator data below 7 TeV, and we consider two independent ensembles by adding either only the TOTEM data or the TOTEM and ATLAS data at the LHC energy region. In the data reductions to each ensemble, the uncertainty regions are evaluated with both one and two standard deviations (∼68%and ∼95%  CL, respectively). Besides the general analytic model, we investigate four particular cases of interest, three of them typical of outstanding models in the literature. We conclude that, within the experimental and theoretical uncertainties and both ensembles, the general model and three particular cases are not able to describe the σtot and ρ data at 13 TeV simultaneously. However, if the discrepancies between the TOTEM and ATLAS data are not resolved, one Pomeron model, associated with double and triple poles and with only 7 free parameters, seems not to be excluded by the complete set of experimental information presently available.

DOI:10.1103/PhysRevD.98.074006

H.Medeiros, D.Lazzaro, T.Kodama

Planetary and Space Science, volume 160

Abstract

The distribution of the rotational frequencies of asteroids is believed to carry important information on their formation and the subsequent evolutionary processes (Burns, 1975). In particular, it is commonly considered that during their formation stage the larger asteroids in the Main Belt have attained a statistical equilibrium (canonical ensemble) in the 3-dimensional isotropic velocity vector space. Subsequently, especially the smaller objects, suffered from various dynamical processes, such as collisions, fragmentation and YORP effect, for example, which modified their spin velocity and direction. In this work we re-examine the spin distribution of asteroids using more recent data and focusing on its statistical aspects, in particular, the dimensionality of the phase space. We find that the presently observed spin distribution of asteroids of any diameter bin is clearly consistent with a 2-dimensional phase space, or even less for the smaller objects. This is true also for those objects with diameter larger than 50 km, whose distribution is usually believed to be consistent with isotropic 3-dimensional Maxwellian. The present result casts open questions on the origin of the asteroids spin.

10.1016/j.pss.2018.04.002

G. S. Denicol, C. Gale, S. Jeon, A. Monnai, B. Schenke, and C.Shen

Phys. Rev. C 98, 034916

Abstract

A hybrid (hydrodynamics + hadronic transport) theoretical framework is assembled to model the bulk dynamics of relativistic heavy-ion collisions at energies accessible in the beam energy scan program at the Relativistic Heavy-Ion Collider and the NA61/SHINE experiment at CERN. The system’s energy-momentum tensor and net-baryon current are evolved according to relativistic hydrodynamics with finite shear viscosity and nonzero net-baryon diffusion. Our hydrodynamic description is matched to a hadronic transport model in the dilute region. With this fully integrated theoretical framework, we present a pilot study of the hadronic chemistry, particle spectra, and anisotropic flow. Phenomenological effects of a nonzero net-baryon current and its diffusion on hadronic observables are presented for the first time. The importance of the hadronic transport phase is also investigated.

10.1103/PhysRevC.98.034916

P. Alba, V. Mantovani Sarti, J. Noronha, J. Noronha-Hostler, P. Parotto, I. Portillo Vazquez, and C. Ratti

Phys. Rev. C 98, 034909

Abstract

The QCD equation of state at zero baryon chemical potential is the only element of the standard dynamical framework to describe heavy ion collisions that can be directly determined from first principles. Continuum extrapolated lattice QCD equations of state have been computed using 2+1 quark flavors (up/down and strange) as well as 2+1+1 flavors to investigate the effect of thermalized charm quarks on QCD thermodynamics. Lattice results have also indicated the presence of new strange resonances that not only contribute to the equation of state of QCD matter but also affect hadronic afterburners used to model the later stages of heavy ion collisions. We investigate how these new developments obtained from first principles calculations affect multiparticle correlations in heavy ion collisions. We compare the commonly used equation of state S95n-v1, which was constructed using what are now considered outdated lattice results and hadron states, to the current state-of-the-art lattice QCD equations of state with 2+1 and 2+1+1 flavors coupled to the most up-to-date hadronic resonances and their decays. New hadronic resonances lead to an enhancement in the hadronic spectra at intermediate pT. Using an outdated equation of state can directly affect the extraction of the shear viscosity to entropy density ratio, η /s , of the quark-gluon plasma and results for different flow observables. The effects of the QCD equation of state on multiparticle correlations of identified particles are determined for both AuAu √{sNN}=200 GeV and PbPb √{sNN}=5.02 TeV collisions. New insights into the v2{2 } to v3{2 } puzzle in ultracentral collisions are found. Flow observables of heavier particles exhibit more nonlinear behavior regardless of the assumptions about the equation of state, which may provide a new way to constrain the temperature dependence of η /s.

10.1103/PhysRevC.98.034909