arXiv subjects

J. D. Orjuela Koop

Publications and source records attributed to J. D. Orjuela Koop.

3 recordsLinked to original sources

arXiv2019

Exploring New Small System Geometries in Heavy Ion Collisions

Relativistic heavy ion collisions produce nuclei-sized droplets of quark-gluon plasma whose expansion is well described by viscous hydrodynamic calculations. Over the past half decade, this formalism was also found to apply to smaller droplets closer to the size of individual nucleons, as produced in $p$$+$$p$ and $p$$+$$A$ collisions. The hydrodynamic paradigm was further tested with a variety of collision species, including $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au producing droplets with different geometries. Nevertheless, questions remain regarding the importance of pre-hydrodynamic evolution and the exact medium properties during the hydrodynamic evolution phase, as well as the applicability of alternative theories that argue the agreement with hydrodynamics is accidental. In this work we explore options for new collision geometries including $p$$+$O and O$+$O proposed for running at the Large Hadron Collider, as well as, $^{4}$He$+$Au, C$+$Au, O$+$Au, and $^{7,9}$Be$+$Au at the Relativistic Heavy Ion Collider.

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arXiv2016

Exploring the Beam Energy Dependence of Flow-Like Signatures in Small System $d+$Au Collisions

Recent analyses of small collision systems, namely $p+p$ and $p+$Pb at the LHC and $p+$Au, $d+$Au and $^{3}$He+Au at RHIC, have revealed azimuthal momentum anisotropies commonly associated with collective flow in larger systems. Viscous hydrodynamics and parton cascade calculations have proved successful at describing some flow-like observables in these systems. These two classes of calculations also confirm these observables to be directly related to the initial geometry of the created medium. However, the question of whether equilibrium dynamics is the dominant driver of the signal remains open, given the short lifetime of small systems. In this regime, pre-equilibrium dynamics and late stage hadronic interactions are expected to play a significant role. Hence, a beam energy scan of small systems---that amounts to varying the initial temperature and the lifetime of the medium---can provide valuable information to shed light on these issues. In this paper, we present predictions from viscous hydrodynamics (SONIC), partonic (AMPT) and hadronic (UrQMD) cascade calculations for elliptic $v_2$ and triangular $v_3$ anisotropy coefficients in $d$+Au at $\sqrt{s_{NN}}$ = 7.7, 20, 39, 62.4 and 200 GeV, corresponding to the expected running at RHIC in 2016. We also present predictions for $d$+Pb at $\sqrt{s_{NN}}$ = 5.02 TeV, an interesting system to compare to existing $p+$Pb data taken at the LHC.

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arXiv2015

Azimuthal Anisotropy Relative to the Participant Plane from AMPT in Central p+Au, d+Au, and $^{3}$He+Au Collisions at $\sqrt{s_{NN}}=200$ GeV

Recent data from p+p and p+Pb collisions at the Large Hadron Collider (LHC), and d+Au and $^3$He+Au collisions at the Relativistic Heavy Ion Collider (RHIC) reveal patterns that---when observed in the collision of heavy nuclei---are commonly interpreted as indicators of a locally equilibrated system in collective motion. The comparison of these data sets, including the forthcoming results from p+Au and p+Al collisions at RHIC, will help to elucidate the geometric dependence of such patterns. It has recently been shown that A-Multi-Phase-Transport-Model (AMPT) can describe some of these features in LHC data with a parton-parton scattering cross section comparable to that required to describe A+A data. In this paper, we extend these studies by incorporating a full wave function description of the $^3$He nucleus to calculate elliptical and triangular anisotropy moments $v_2$ and $v_3$ for p+Au, d+Au and $^3$He+Au collisions at the RHIC top energy of 200 GeV. We find reasonable agreement with the measured $v_2$ in d+Au and $^3$He+Au and $v_3$ in $^3$He+Au for transverse momentum ($p_{T}$) $\lesssim$ 1 GeV/c, but underestimate these measurements for higher values of \pt. We predict a pattern of coefficients ($v_{2}$, $v_{3}$) for \pau, dominated by differences in the number of induced local hot spots (i.e. one, two, or three) arising from intrinsic geometry. Additionally, we examine how this substantial azimuthal anisotropy accrues during each individual evolutionary phase of the collision in the AMPT model. The possibility of a simultaneous description of RHIC- and LHC-energy data, the suite of different geometries, and high multiplicity p+p data is an exciting possibility for understanding the underlying physics in these systems.

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