arXiv subjects

J. L. Nagle

Publications and source records attributed to J. L. Nagle.

At least 19 recordsLinked to original sources

arXiv2025

Selection bias effects on high-$p_\mathrm{T}$ yield and correlation measurements in Oxygen+Oxygen collisions

Oxygen+Oxygen (O+O) collisions at RHIC and the LHC offer a unique experimental opportunity to observe the onset of jet quenching in intermediate relativistic collision systems. As with the smaller proton-nucleus or larger nucleus-nucleus systems, measurements of centrality-selected high-$p_\mathrm{T}$ processes in O+O collisions are expected to be sensitive to selection bias effects, which will be necessary to quantify or mitigate before a definitive conclusion on the presence of jet quenching. Using two Monte Carlo heavy-ion event generators, we provide a survey of centrality bias effects on high-$p_\mathrm{T}$ yield and correlation measurements. Some highlights of our findings include that (1) bias factors for the accessible kinematic range at RHIC show a non-trivial $p_\mathrm{T}$ dependence, compared to a negligible one at the LHC given the smaller accessible Bjorken-$x$ range, (2) centrality definitions based on multiplicity are less sensitive to bias effects than those based on the transverse energy, (3) the Angantyr generator gives qualitatively similar but larger-magnitude bias factors than HIJING, and (4) correlation measurements have a much smaller sensitivity to bias effects than do yield measurements. The findings here are intended to guide the experimental design and interpretation of O+O jet quenching and other hard-process measurements.

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arXiv2023

Hot QCD White Paper

Hot QCD physics studies the nuclear strong force under extreme temperature and densities. Experimentally these conditions are achieved via high-energy collisions of heavy ions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). In the past decade, a unique and substantial suite of data was collected at RHIC and the LHC, probing hydrodynamics at the nucleon scale, the temperature dependence of the transport properties of quark-gluon plasma, the phase diagram of nuclear matter, the interaction of quarks and gluons at different scales and much more. This document, as part of the 2023 nuclear science long range planning process, was written to review the progress in hot QCD since the 2015 Long Range Plan for Nuclear Science, as well as highlight the realization of previous recommendations, and present opportunities for the next decade, building on the accomplishments and investments made in theoretical developments and the construction of new detectors. Furthermore, this document provides additional context to support the recommendations voted on at the Joint Hot and Cold QCD Town Hall Meeting, which are reported in a separate document.

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arXiv2021

Checking Non-Flow Assumptions and Results via PHENIX Published Correlations in $p$$+$$p$, $p$$+$Au, $d$$+$Au, $^3$He$+$Au at $\sqrt{s_{NN}}$ = 200 GeV

Recently the PHENIX Collaboration has made available two-particle correlation Fourier coefficients for multiple detector combinations in minimum bias p+p and 0-5% central p+Au, d+Au, 3He+Au collisions at 200 GeV [1]. Using these coefficients for three sets of two-particle correlations, azimuthal anisotropy coefficients $v_2$ and $v_3$ are extracted for midrapidity charged hadrons as a function of transverse momentum. In this paper, we use the available coefficients to explore various non-flow hypotheses as well as compare the results with theoretical model calculations. The non-flow methods fail basic closure tests with AMPT and PYTHIA/ANGANTYR, particularly when including correlations with particles in the low multiplicity light-projectile going direction. In data, the non-flow adjusted $v_2$ results are modestly lower in p+Au and the adjusted $v_3$ results are more significantly higher in p+Au and d+Au. However, the resulting higher values for the ratio $v_3/v_2$ in p+Au at RHIC compared to p+Pb at the LHC is additional evidence for a significant over-correction. Incorporating these additional checks, the conclusion that these flow coefficients are dominated by initial geometry coupled with final-state interactions (e.g.~hydrodynamic expansion of quark-gluon plasma) remains true, and explanations based on initial-state glasma are ruled out. The detailed balance between intrinsic and fluctuation-driven geometry and the exact role of weakly versus strongly-coupled pre-hydrodynamic evolution remains an open question for triangular flow, requiring further theoretical and experimental investigation.

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arXiv2021

Exploring Origins for Correlations between Flow Harmonics and Transverse Momentum in Small Collision Systems (Unambiguous Ambiguity)

High statistics data sets from experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) with small and large collision species have enabled a wealth of new flow measurements, including the event-by-event correlation between observables. One exciting such observable $ρ(v^{2}_{n},[p_{T}])$ gauges the correlation between the mean transverse momentum of particles in an event and the various flow coefficients ($v_n$) in the same event [1]. Recently it has been proposed that very low multiplicity events may be sensitive to initial-state glasma correlations [2] rather than flow-related dynamics. We find utilizing the IP-JAZMA framework that the color domain explanation for the glasma results are incomplete. We then explore predictions from PYTHIA-8, and the version for including nuclear collisions called PYTHIA-ANGANTYR, which have only non-flow correlations and the AMPT model which has both non-flow and flow-type correlations. We find that PYTHIA-ANGANTYR has non-flow contributions to $ρ(v^{2}_{n},[p_{T}])$ in p+O, p+Pb, O+O collisions that are positive at low multiplicity and comparable to the glasma correlations. It is striking that in PYTHIA-8 in p+p collisions there is actually a sign-change from positive to negative $ρ(v^{2}_{n},[p_{T}])$ as a function of multiplicity. The AMPT results match the experimental data general trends in Pb+Pb collisions at the LHC, except at low multiplicity where AMPT has the opposite sign. In p+Pb collisions, AMPT has the opposite sign from experimental data and we explore this within the context of parton geometry. Predictions for p+O, O+O, and Xe+Xe are also presented.

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arXiv2020

Gluonic Hot Spot Initial Conditions in Heavy-Ion Collisions

The initial conditions in heavy-ion collisions are calculated in many different frameworks. The importance of nucleon position fluctuations within the nucleus and sub-nucleon structure has been established when modeling initial conditions for input to hydrodynamic calculations. However, there remain outstanding puzzles regarding these initial conditions, including the measurement of the near equivalence of the elliptical $v_{2}$ and triangular $v_{3}$ flow coefficients in ultra-central 0-1% Pb+Pb collisions at the LHC. Recently a calculation termed MAGMA incorporating gluonic hot spots via two-point correlators in the Color Glass Condensate framework, and no nucleons, provided a simultaneous match to these flow coefficients measured by the ATLAS experiment, including in ultra-central 0-1% collisions. Our calculations reveal that the MAGMA initial conditions do not describe the experimental data when run through full hydrodynamic SONIC simulations or when the hot spots from one nucleus resolve hot spots from the other nucleus, as predicted in the Color Glass Condensate framework. We also explore alternative initial condition calculations and discuss their implications.

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arXiv2019

Examination of Flow and Non-Flow Factorization Methods in Small Collision Systems

Two particle correlations have been used extensively to study hydrodynamic flow patterns in heavy-ion collisions. In small collision systems, such as $p$$+$$p$ and $p$$+$$A$, where particle multiplicities are much smaller than in $A$$+$$A$ collisions, non-flow effects from jet correlations, momentum conservation, particle decays, etc. can be significant, even when imposing a large pseudorapidity gap between the particles. A number of techniques to subtract the non-flow contribution in two particle correlations have been developed by experiments at the Large Hadron Collider (LHC) and then used to measure particle flow in $p$$+$$p$ and $p$$+$Pb collisions. Recently, experiments at the Relativistic Heavy Ion Collider (RHIC) have explored the possibility of adopting these techniques for small collision systems at lower energies. In this paper, we test these techniques using Monte Carlo generators PYTHIA and HIJING, which do not include any collective flow, and AMPT, which does. We find that it is crucial to examine the results of such tests both for correlations integrated over particle transverse momentum $p_T$ and differentially as a function of $p_T$. Our results indicate reasonable non-flow subtraction for $p$$+$$p$ collisions at the highest LHC energies, while failing if applied to $p$$+$$p$ collisions at RHIC. In the case of $p$$+$Au collisions at RHIC, both HIJING and AMPT results indicate a substantial over-subtraction of non-flow for $p_{T}\gtrsim1~{\rm GeV}/c$ and hence an underestimate of elliptic flow.

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arXiv2019

The Skinny on Bulk Viscosity and Cavitation in Heavy Ion Collisions

Relativistic heavy ion collisions generate nuclear-sized droplets of quark-gluon plasma (QGP) that exhibit nearly inviscid hydrodynamic expansion. Smaller collision systems such as p+Au, d+Au, and $^{3}$He+Au at the Relativistic Heavy Ion Collider, as well as p+Pb and high-multiplicity p+p at the Large Hadron Collider may create even smaller droplets of QGP. If so, the standard time evolution paradigm of heavy ion collisions may be extended to these smaller systems. These small systems present a unique opportunity to examine pre-hydrodynamic physics and extract properties of the QGP, such as the bulk viscosity, where the short lifetimes of the small droplets makes them more sensitive to these contributions. Here we focus on the influence of bulk viscosity, its temperature dependence, and cavitation effects on the dynamics in small and large systems using the publicly available hydrodynamic codes SONIC and MUSIC. We also compare pre-hydrodynamic physics in different frameworks including AdS/CFT strong coupling, IP-GLASMA weak coupling, and free streaming or no coupling.

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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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arXiv2018

Design and Beam Test Results for the sPHENIX Electromagnetic and Hadronic Calorimeter Prototypes

The super Pioneering High Energy Nuclear Interaction eXperiment (sPHENIX) at the Relativistic Heavy Ion Collider (RHIC) will perform high precision measurements of jets and heavy flavor observables for a wide selection of nuclear collision systems, elucidating the microscopic nature of strongly interacting matter ranging from nucleons to the strongly coupled quark-gluon plasma. A prototype of the sPHENIX calorimeter system was tested at the Fermilab Test Beam Facility as experiment T-1044 in the spring of 2016. The electromagnetic calorimeter (EMCal) prototype is composed of scintillating fibers embedded in a mixture of tungsten powder and epoxy. The hadronic calorimeter (HCal) prototype is composed of tilted steel plates alternating with plastic scintillator. Results of the test beam reveal the energy resolution for electrons in the EMCal is $2.8\%\oplus~15.5\%/\sqrt{E}$ and the energy resolution for hadrons in the combined EMCal plus HCal system is $13.5\%\oplus 64.9\%/\sqrt{E}$. These results demonstrate that the performance of the proposed calorimeter system satisfies the sPHENIX specifications.

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arXiv2018

Assessing saturation physics explanations of collectivity in small collision systems with the IP-Jazma model

Experimental measurements in collisions of small systems from p+p to p/d/3He+A at RHIC and the LHC reveal particle emission patterns that are strikingly similar to those observed in A+A collisions. One explanation of these patterns is the formation of small droplets of quark-gluon plasma followed by hydrodynamic evolution. A geometry engineering program was proposed [1] to investigate these emission patterns, and the experimental data from that program in p+Au, d+Au, 3He+Au collisions for elliptic and triangular anisotropy coefficients v2 and v3 follow the pattern predicted by hydrodynamic calculations [2]. One alternative approach, referred to as initial-state correlations, suggests that for small systems the patterns observed in the final-state hadrons are encoded at the earliest moments of the collision, and therefore require no final-state parton scattering or hydrodynamic evolution [3,4]. Recently, new calculations using only initial-state correlations, in the dilute-dense approximation of gluon saturation physics, reported striking agreement with the v2 patterns observed in p/d/3He+Au data at RHIC [5]. The reported results are counterintuitive and thus we aim here to reproduce some of the basic features of these calculations. In this first investigation, we provide a description of our model, IP-Jazma, and investigate its implications for saturation scales, multiplicity distributions and eccentricities, reserving for later work the analysis of momentum spectra and azimuthal anisotropies. We find that our implementation of the saturation physics model reproduces the results of the earlier calculation of the multiplicity distribution in d+Au collisions at RHIC. However, our investigations, together with existing data, call into question some of the essential elements reported in Ref. [5].

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arXiv2018

A Quasiparticle Transport Explanation for Collectivity in the Smallest of Collision Systems (p + p and e+e-)

The field of heavy ion physics is at a crossroads in understanding experimental signatures of collectivity in small collision systems, p + p and p(d/3He) + A, at RHIC and the LHC. A wealth of data obtained in the latter class of asymmetric systems indicate the existence of particle emission patterns similar to those observed in larger A+A collisions [1], raising the question of whether the same physics is at play in both cases, lest the cruelty of nature be somehow exposed. In this talk, we present an extension of earlier studies using the quasiparticle transport model AMPT to predict particle emission patterns in the smallest of collision systems, namely p + p and e+e-. The e+e- results have been previously published [2] and we thus focus here on an extended set of calculations, as shown at the Quark Matter 2018 Conference.

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arXiv2018

Small System Collectivity in Relativistic Hadron and Nuclear Collisions

The bulk motion of nuclear matter at the ultra-high temperatures created in heavy-ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider is well described in terms of nearly inviscid hydrodynamics, thereby establishing this system of quarks and gluons as the most perfect fluid in nature. A revolution in the field is underway, spearheaded by the discovery of similar collective, fluid-like phenomena in much smaller systems including p+p, p+A, d+Au, and $^3$He$+$Au collisions. We review these exciting new observations and their implications.

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arXiv2017

Are minimal conditions for collectivity met in e+e- collisions?

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.

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arXiv2017

To CME or not to CME? Implications of p+Pb measurements of the chiral magnetic effect in heavy ion collisions

The Chiral Magnetic Effect (CME) is a fundamental prediction of QCD, and various observables have been proposed in heavy ion collisions to access this physics. Recently the CMS Collaboration \cite{Khachatryan:2016got} has reported results from p+Pb collisions at 5.02 TeV on one such observable, the three-point correlator. The results are strikingly similar to those measured at the same particle multiplicity in Pb+Pb collisions, which have been attributed to the CME. This similarity, combined with two key assumptions about the magnetic field in p+Pb collisions, presents a major challenge to the CME picture. These two assumptions as stated in the CMS paper are (1) that the magnetic field in p+Pb collisions is smaller than that in Pb+Pb collisions and (2) that the magnetic field direction is uncorrelated with the flow angle. We test these two postulates in the Monte Carlo Glauber framework and find that the magnetic fields are not significantly smaller in central p+Pb collisions, however the magnetic field direction and the flow angle are indeed uncorrelated. The second finding alone gives strong evidence that the three-point correlator signal in Pb+Pb and p+Pb is not an indication of the CME. Similar measurements in d+Au over a range of energies accessible at RHIC would be elucidating. In the same calculational framework, we find that even in Pb+Pb collisions, where the magnetic field direction and the flow angle are correlated, there exist large inhomogeneities that are on the size scale of topological domains. These inhomogeneities need to be incorporated in any detailed CME calculation.

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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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arXiv2016

Consequences of high-$x$ proton size fluctuations in small collision systems at RHIC

Recent measurements of jet production rates at large transverse momentum ($p_T$) in the collisions of small projectiles with large nuclei at RHIC and the LHC indicate that they have an unexpected relationship with estimates of the collision centrality. One compelling interpretation of the data is that it captures an $x_p$-dependent decrease in the average interaction strength of the nucleon in the projectile undergoing a hard scattering. A weakly interacting or "shrinking" nucleon in the projectile strikes fewer nucleons in the nucleus, resulting in a particular pattern of centrality-dependent modifications to high-$p_T$ processes. We describe a simple one-parameter geometric implementation of this picture within a modified Monte Carlo Glauber model tuned to $d$$+$Au jet data, and explore two of its major consequences. First, the model predicts a particular projectile-species dependence to the centrality dependence at high-$x_p$, opposite to that expected from an energy loss effect. Second, we find that some of the large centrality dependence observed for forward di-hadron production in $d$$+$Au collisions at RHIC may arise from the physics of the "shrinking" projectile nucleon, in addition to impact parameter-dependent shadowing or saturation effects at low nuclear-$x$. We conclude that analogous measurements in recently collected $p$$+$Au and $^3$He$+$Au collision data at RHIC can provide a unique test of these predictions.

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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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arXiv2015

Particle spectra and HBT radii for simulated central nuclear collisions of C+C, Al+Al, Cu+Cu, Au+Au, and Pb+Pb from Sqrt(s)=62.4-2760 GeV

We study the temperature profile, pion spectra and HBT radii in central symmetric and boost-invariant nuclear collisions using a super hybrid model for heavy-ion collisions (SONIC) combining pre-equilibrium flow with viscous hydrodynamics and late-stage hadronic rescatterings. In particular, we simulate Pb+Pb collisions at Sqrt(s)=2.76 TeV, Au+Au, Cu+Cu, Al+Al, and C+C collisions at Sqrt(s)=200 GeV and Au+Au, Cu+Cu collisions at Sqrt(s)=62.4 GeV. We find that SONIC provides a good match to the pion spectra and HBT radii for all collision systems and energies, confirming earlier work that a combination of pre-equilibrium flow, viscosity and QCD equation of state can resolve the so-called HBT puzzle. For reference, we also show p+p collisions at Sqrt(s)=7 TeV. We make tabulated data for the 2+1 dimensional temperature evolution of all systems publicly available for the use in future jet energy loss or similar studies.

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