The study of numerous physics effects in small collision systems requires a careful characterization of the event geometry. In particular, many such phenomena have a strong dependence on the impact ...parameter of the collision. We describe the methodology utilized by PHENIX to select centrality classes in d+Au collisions via cuts on charge deposited at backward (Au-going) rapidity. The measured charge can be mapped to other geometric quantites using a Monte Carlo Glauber model. We also describe how autocorrelations between the process of interest and the backward rapidity charge introduce bias effects that alter the measurement of centrality-dependent invariant yields. Our framework provides a method to compute correction factors to account for such effects. We discuss their calculation and validation using the HIJING Monte Carlo Generator. It is found that centrality bias correction factors are small and slightly pT dependent for d+Au collisions at 200 GeV, yet an order of magnitude larger and strongly pT dependent for p+Pb collisions at 5.02 TeV. The implications of such corrections are discussed for selected physics observables and effects.
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.
Phys. Rev. C 93, 044910 (2016) 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.
Phys. Rev. C 92, 054903 (2015) 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.
Signatures of collective behavior have been measured in highly relativistic p+p collisions, as well as in p+A, d+A, and 3He+A collisions. Numerous particle correlation measurements in these systems ...have been successfully described by calculations based on viscous hydrodynamic and transport models. These observations raise the question of the minimum necessary conditions for a system to exhibit collectivity. Recently, numerous scientists have raised the question of whether the quarks and gluons generated in e+e- collisions may satisfy these minimum conditions. In this paper we explore possible signatures of collectivity, or lack thereof, in e+e- collisions utilizing A Multi-Phase Transport (AMPT) framework which comprises melted color strings, parton scattering, hadronization, and hadron re-scattering.
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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