Analyzing radial flow features inp-Pb andp-pcollisions at several TeV by studying identified-particle production with the event generator EPOS3

Abstract

Experimental transverse momentum spectra of identified particles in p-Pb collisions at 5.02 TeV show many similarities to the corresponding Pb-Pb results, the latter ones usually being interpreted in term of hydrodynamic flow. We analyse these data using EPOS3, an event generator based on a 3D+1 viscous hydrodynamical evolution starting from flux tube initial conditions, which are generated in the Gribov-Regge multiple scattering framework. An individual scattering is referred to as Pomeron, identified with a parton ladder, eventually showing up as flux tubes (or strings). Each parton ladder is composed of a pQCD hard process, plus initial and final state linear parton emission. Nonlinear effects are considered by using saturation scales Qs, depending on the energy and the number of participants connected to the Pomeron in question. We compute transverse momentum (pt) spectra of pions, kaons, protons, lambdas, and Ξ baryons in p-Pb and p-p scattering, compared to experimental data and many other models. In this way we show in a quantitative fashion that p-Pb data (and even p-p ones) show the typical "flow effect" of enhanced particle production at intermediate pt values, more and more visible with increasing hadron mass.

Measurement of D-meson production versus multiplicity in p-Pb collisions at s N N = 5.02 $$ \sqrt{{\mathrm{s}}_{\mathrm{NN}}}=5.02 $$ TeV

“…The increasing yield in pp data can be described by calculations taking into account the contribution of Multiple-Parton Interactions (MPI) [23][24][25], by the influence of the interactions between colour sources in the percolation model [33,34], or by the effect of the initial conditions of the collision followed by a hydrodynamic evolution computed with the EPOS 3 event generator [35,36] where the individual scatterings are identified with parton ladders. In p-Pb collisions, the multiplicity dependence of heavy-flavour production is also affected by the presence of multiple binary nucleon-nucleon interactions, and the initial conditions of the collision are modified due to CNM effects.…”

“…These results suggest that the enhancement probably originates in short-distance production processes, and is not influenced by hadronisation mechanisms. The enhancement is quantitatively described by calculations including MPI contributions, namely percolation model estimates [33,34], the EPOS 3 event generator [35,36] and PYTHIA 8.157 calculations [37].…”

EPOS LHC: Test of collective hadronization with data measured at the CERN Large Hadron Collider

“…We will call it the nuclear AA flow, characterized by the maximal radial rapidity y AA rad . But in the case of a light system, such as p-p, using EPOS 2 or 3 with a realistic treatment of the hydrodynamical evolution with proper hadronization, such an effect was not observed [16,20,28]. In that case the large flow comes from the quick expansion of the very small volume of the core.…”

“…The EPOS version EPOS LHC v3400 presented here differs from EPOS 2.x [15] and EPOS 3.x [16] (under development) in that it does not take advantage of the complete 3D hydro calculation followed by the hadronic cascade done in EPOS 2 or 3, but it is a released version which is freely available for any user [17]. The fast covariant approach used in EPOS 1.99 is still used but with an improved flow parametrization as described later.…”

Impact of the initial size of spatial fluctuations on the collective flow in Pb–Pb collisions at $\sqrt{{{s}_{{\rm NN}}}}$ = 2.76 TeV

“…A similar question has been addressed in the ideal or viscous hydro calculations by the authors of Refs. [31,32,33,34,35,36,37] which have found some sensitivity with respect to higher moments v n .…”