arXiv subjects

Clint Young

Publications and source records attributed to Clint Young.

At least 19 recordsLinked to original sources

arXiv2016

Relating Measurable Correlations in Heavy Ion Collisions to Bulk Properties of Equilibrated QCD Matter

In order to compare theoretical calculations of thermal fluctuations of conserved quantities, such as charge susceptibilities or the specific heat, to experimentally measured correlations and fluctuations in heavy ion collisions, one must confront the reality of changing conditions within the collision environment, and transport of conserved quantities within the finite duration of the expansion and dissolution of the reaction. In previous work, fluctuations of conserved charges from lattice calculations, where charge is allowed to fluctuate within the designated volume consistent with the grand canonical ensemble, was linked to correlations in heavy-ion collisions, which accounted for the finite time with which to transport absolutely conserved quanatities. In this case details of the correlations were related to the evolution of the susceptibility. In this work, this paradigm is extended to compare fluctuations of momentum or energy to transverse energy correlations that can be measured in heavy-ion collisions. The sensitivity of these correlations to the equation of state, viscosity and diffusion is illustrated by considering simple models without transverse expansion. Only correlations in relative spatial rapidity are discussed here, but the prospects for extending these ideas to realistic calculations and for making realistic connections with experiment are discussed.

nucl-th↗

arXiv2016

Determining Health Utilities through Data Mining of Social Media

'Health utilities' measure patient preferences for perfect health compared to specific unhealthy states, such as asthma, a fractured hip, or colon cancer. When integrated over time, these estimations are called quality adjusted life years (QALYs). Until now, characterizing health utilities (HUs) required detailed patient interviews or written surveys. While reliable and specific, this data remained costly due to efforts to locate, enlist and coordinate participants. Thus the scope, context and temporality of diseases examined has remained limited. Now that more than a billion people use social media, we propose a novel strategy: use natural language processing to analyze public online conversations for signals of the severity of medical conditions and correlate these to known HUs using machine learning. In this work, we filter a dataset that originally contained 2 billion tweets for relevant content on 60 diseases. Using this data, our algorithm successfully distinguished mild from severe diseases, which had previously been categorized only by traditional techniques. This represents progress towards two related applications: first, predicting HUs where such information is nonexistent; and second, (where rich HU data already exists) estimating temporal or geographic patterns of disease severity through data mining.

cs.CL↗

arXiv2015

Electromagnetic recombination spectra at the quark-hadron phase transition

When quarks hadronize, they accelerate. Because they carry electric charge, they must radiate light as they accelerate and hadronize. This is true not only in jets but also in heavy ion collisions, where a thermalized plasma of quarks and gluons cools into a gas of hadrons. First, direct emission of photons from two quarks coalescing into pions is calculated using the quark-meson model. The yield of final-state photons to pions is found to be about $e^2/g^2_{πqq}$, which is on the order of a percent. Second, the yield of photons from the decay of highly excited color singlets, which may exist ephemerally during hadronizaton, is estimated. Because these contributions occur late in the reaction, they should carry significant elliptic flow, which may help explain the large observed flow of direct photons at RHIC by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC). The enhanced emission also helps explain PHENIX's surprisingly large observed $γ/π$ ratio.

nucl-th↗

arXiv2015

Dissipative effects on quarkonium spectral functions

Quarkonium at finite temperature is described as an open quantum system whose dynamics are determined by a potential $V_R({\bf x})$ and drag coefficient $η$, using a path integral with a non-local term. Path-integral Monte Carlo calculations determine the Euclidean Green function for this system to an accuracy greater than one part in a thousand and the maximum entropy method is used to determine the spectral function; challenges facing any kind of deconvolution are discussed in detail with the aim of developing intuition for when deconvolution is possible. Significant changes to the quarkonium spectral function in the $1S$ channel are found, suggesting that any description of quarkonium at finite temperature, using a potential, must also carefully consider the effect of dissipation.

nucl-th↗

arXiv2013

Extracting jet transport coefficient from jet quenching at RHIC and LHC

Within five different approaches to parton propagation and energy loss in dense matter, a phenomenological study of experimental data on suppression of large $p_T$ single inclusive hadrons in heavy-ion collisions at both RHIC and LHC was carried out. The evolution of bulk medium used in the study for parton propagation was given by 2+1D or 3+1D hydrodynamic models which are also constrained by experimental data on bulk hadron spectra. Values for the jet transport parameter $\hat q$ at the center of the most central heavy-ion collisions are extracted or calculated within each model, with parameters for the medium properties that are constrained by experimental data on the hadron suppression factor $R_{AA}$. For a quark with initial energy of 10 GeV we find that $\hat q\approx 1.2 \pm 0.3$ GeV$^2$/fm at an initial time $τ_0=0.6$ fm/$c$ in Au+Au collisions at $\sqrt{s}=200$ GeV/n and $\hat q\approx 1.9 \pm 0.7 $ GeV$^2$/fm in Pb+Pb collisions at $\sqrt{s}=2.76 $ TeV/n. Compared to earlier studies, these represent significant convergence on values of the extracted jet transport parameter, reflecting recent advances in theory and the availability of new experiment data from the LHC.

nucl-th↗

arXiv2013

Dilepton emission in high-energy heavy-ion collisions with viscous hydrodynamics

The invariant mass spectrum and the elliptic flow of lepton pairs produced in relativistic heavy-ion collisions at RHIC are studied with viscous hydrodynamics. The effects of viscous corrections on dilepton observables are explored. The lepton pairs originating from charm quarks evolving in the viscous background are seen to be a good probe of quark energy loss and gain, as quantified by the dilepton spectrum and by the dilepton elliptic flow.

nucl-th↗

arXiv2013

Numerical integration of thermal noise in relativistic hydrodynamics

Thermal fluctuations affect the dynamics of systems near critical points, the evolution of the early universe, and two-particle correlations in heavy-ion collisions. For the latter, numerical simulations of nearly-ideal, relativistic fluids are necessary. The correlation functions of noise in relativistic fluids are calculated, stochastic integration of the noise in 3+1-dimensional viscous hydrodynamics is implemented, and the effect of noise on observables in heavy-ion collisions is discussed. Thermal fluctuations will cause significant variance in the event-by-event distributions of integrated v2 while changing average values even when using the same initial conditions, suggesting that including thermal noise will lead to refitting of the hydrodynamical parameters with implications for understanding the physics of hot QCD.

nucl-th↗

arXiv2012

MUSIC with the UrQMD Afterburner

As RHIC is entering the precision measurement era and the LHC is producing a copious amount of new data, the role of 3+1D event-by-event viscous hydrodynamics is more important than ever to understand the bulk data as well as providing the background for hard probes. For more meaningful comparison with the experimental data, it is also important that hydrodynamics be coupled to the hadronic afterburner. In this proceeding we report on preliminary results of coupling MUSIC with UrQMD.

hep-ph↗

arXiv2012

Realistic modelling of jets in heavy-ion collisions

The reconstruction of jets in heavy-ion collisions provides insight into the dynamics of hard partons in media. Unlike the spectrum of single hadrons, the spectrum of jets is highly sensitive to $\hat{q}_{\perp}$, as well as being sensitive to partonic energy loss and radiative processes. We use MARTINI, an event generator, to study how finite-temperature processes at leading order affect dijets.

nucl-th↗

arXiv2011

Viscous photons in relativistic heavy ion collisions

Theoretical studies of the production of real thermal photons in relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are performed. The space-time evolution of the colliding system is modelled using MUSIC, a 3+1D relativistic hydrodynamic simulation, using both its ideal and viscous versions. The inclusive spectrum and its azimuthal angular anisotropy are studied separately, and the relative contributions of the different photon sources are highlighted. It is shown that the photon v2 coefficient is especially sensitive to the details of the microscopic dynamics like the equation of state, the ratio of shear viscosity over entropy density, eta/s, and to the morphology of the initial state.

hep-ph↗

arXiv2011

MARTINI for heavy quarks: initialization, parton evolution, and hadronization with event generation

We present additions to the MARTINI event generator for examining heavy quarks and quarkonia in heavy-ion collisions. All stages of a heavy-ion collision affect the observables associated with heavy quarks: the initial phase space of the heavy quarks are sampled with PYTHIA8.1, the heavy quarks are evolved using Langevin dynamics and a 3+1-dimensional hydrodynamical description of the heavy-ion collision, and are fragmented and hadronized using a modified version of the color evaporation model that takes into account non-trivial evolution in position space, as well as the possibility of recombinant quarkonium production in heavy-ion collisions. We use this to re-examine the production of quarkonium at RHIC, and anticipating vertex detection we predict yields of B_c mesons at RHIC and the LHC.

nucl-th↗

arXiv2011

Monte-Carlo simulation of jets in heavy-ion collisions

We present Monte-Carlo simulations of jet evolution in lead-lead collisions at the Large Hadron Collider (LHC) at CERN focusing on the dijet asymmetry measured by the ATLAS and CMS collaborations. In the simulation, hard partons are interacting with the hydrodynamical background medium, undergoing radiative and collisional processes. The measured dijet asymmetry is well described by the simulation and is hence consistent with partonic energy loss in a hot, strongly-interacting medium.

hep-ph↗

arXiv2011

Photons at RHIC: The role of viscosity and of initial state fluctuations

We study real photons produced in heavy ion collisions at RHIC, and we calculate their spectrum and its azimuthal momentum anisotropy. The photons from a variety of sources are included, and the interplay and the time-evolution of those sources are modelled in a full 3D hydrodynamic simulation. We quantify the v_2 of thermal photons produced in ideal and viscous fluids, and the consequences of using different initial conditions are explored.

hep-ph↗

arXiv2011

Dijet asymmetry at the Large Hadron Collider

The MARTINI numerical simulation allows for direct comparison of theoretical model calculations and the latest results for dijet asymmetry from the ATLAS and CMS collaborations. In this paper, partons are simulated as undergoing radiative and collisional processes throughout the evolution of central lead-lead collisions at the Large Hadron Collider. Using hydrodynamical background evolution determined by a simulation which fits well with the data on charged particle multiplicities from ALICE and a value of $α_s\approx 0.25-0.3$, the dijet asymmetry is found to be consistent with partonic energy loss in a hot, strongly-interacting medium.

nucl-th↗

arXiv2010

Quarkonium above deconfinement as an open quantum system

Quarkonium at temperatures above deconfinement is modeled as an open quantum system, whose dynamics is determined not just by a potential energy and mass, but also by a drag coefficient which characterizes its interaction with the medium. The reduced density matrix for a heavy particle experiencing dissipative forces is expressed as an integral over paths in imaginary time and evaluated numerically. We demonstrate that dissipation could affect the Euclidean heavy-heavy correlators calculated in lattice simulations at temperatures just above deconfinement.

nucl-th↗

arXiv2009

Recombinant Charmonium in strongly coupled Quark-Gluon Plasma

We update our previous work of a Langevin-with-interaction model for charmonium in heavy-ion collisions, by considering the effect due to recombination. We determine the contribution to J/psi yields from charm-anticharm pairs whose constituent quarks originate from two different hard processes. Like the surviving J/psi states, the recombinant J/psi also undergo both a stochastic interaction, determined by a hydrodynamical simulation of the heavy-ion collision, and an interaction determined by the heavy quark-antiquark potentials measured on the lattice for appropriate temperatures. From the results of these simulations, we determine both the direct and the recombinant contribution to the J/psi yields for RHIC conditions, and find that for central collisions, between 30% and 50% of the J/psi yield is due to recombinant production. We compare our results with other models and look for how the recombinant contribution differs from the surviving contribution in the differential p_t yields. Including the recombinant contribution improves the agreement with the latest analysis of charmonium at RHIC, which shows an absence of anomalous suppression except in the most central collisions.

nucl-th↗

arXiv2009

Effective potentials for heavy quarks above deconfinement

Using methods previously developed by Kelbg and others for creating effective potentials for electron-ion plasmas, we investigate quarkonium potentials above deconfinement. Using results for the internal energy of a static quark-antiquark pair, a set of effective potentials are constructed that take into account quantum effects and symmetry conditions. Bound state effects are explicitly included in order to account for the strongly coupled nature of plasmas. It is hoped that these effective potentials will be useful in simulations of heavy quarks or plasma quasiparticles when the dynamics is treated classically.

nucl-th↗

arXiv2008

Charmonium in strongly coupled quark-gluon plasma

The growing consensus that a strongly-coupled quark-gluon plasma (sQGP) has been observed at the SPS and RHIC experiments suggests a different framework for examining heavy quark dynamics. We present both semi-analytical treatment of Fokker-Planck (FP) evolution in pedagogical examples and numerical Langevin simulations of evolving charm quark-antiquark pairs on top of a hydrodynamically expanding fireball. In this way, we may conclude that the survival probability of bound charmonia states is greater than previously estimated, as the spatial equilibration of pairs proceeds through a ``slowly dissolving lump'' stage related to the pair interaction.

nucl-th↗