arXiv subjects

J. L. Nagle

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

At least 37 records · Page 2Linked to original sources

arXiv2014

Exploiting Intrinsic Triangular Geometry in Relativistic He3+Au Collisions to Disentangle Medium Properties

Recent results in d+Au and p+Pb collisions at RHIC and the LHC provide evidence for collective expansion and flow of the created medium. We propose a control set of experiments to directly compare particle emission patterns from p+Au, d+Au, and He3+Au or t+Au collisions at the same sqrt(sNN). Using Monte Carlo Glauber we find that a He3 or triton projectile, with a realistic wavefunction description, induces a significant intrinsic triangular shape to the initial medium and that, even with viscous damping, this survives into a significant third order flow moment v3. By comparing systems with one, two, and three initial hot spots, one can disentangle the effects from the initial spatial distribution of the deposited energy and viscous damping. These are key tools to answering the question of how small a droplet of matter is necessary to form a quark-gluon plasma described by nearly inviscid hydrodynamics.

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arXiv2012

Jet-Underlying Event Separation Method for Heavy Ion Collisions at the Relativistic Heavy Ion Collider

Reconstructed jets in heavy ion collisions are a crucial tool for understanding the quark-gluon plasma. The separation of jets from the underlying event is necessary particularly in central heavy ion reactions in order to quantify medium modifications of the parton shower and the response of the surrounding medium itself. There have been many methods proposed and implemented for studying the underlying event substructure in proton-proton and heavy ion collisions. In this paper, we detail a method for understanding underlying event contributions in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV utilizing the HIJING event generator. This method, extended from previous work by the ATLAS collaboration, provides a well-defined association of "truth jets" from the fragmentation of hard partons with "reconstructed jets" using the anti-$k_T$ algorithm. Results presented here are based on an analysis of 750M minimum bias HIJING events. We find that there is a substantial range of jet energies and radius parameters where jets are well separated from the background fluctuations (often termed "fake jets") that make jet measurements at RHIC a compelling physics program.

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arXiv2010

Theoretical Modeling of J/psi Yield Modifications in Proton (Deuteron) - Nucleus Collisions at High Energy

Understanding the detailed production and hadronization mechanisms for heavy quarkonia and their modification in a nuclear environment presents one of the major challenges in QCD. Calculations including nuclear-modified parton distribution functions (nPDFs) and fitting of break-up cross sections (sigma_breakup) as parameters have been successful at describing many features of J/psi modification in proton(deuteron)-nucleus collisions. In this paper, we extend these calculations to explore different geometric dependencies of the modification and confront them with new experimental results from the PHENIX experiment. We find that no combination of nPDFs and sigma_breakup, regardless of the nPDF parameter set and the assumed geometric dependence, can simultaneously describe the entire rapidity and centrality dependence of J/psi modifications in d+Au collisions at sqrt(s_NN) = 200 GeV. We also compare the data with coherence calculations and find them unable to describe the full rapidity and centrality dependence as well. We discuss how these calculations might be extended and further tested, in addition to discussing other physics mechanisms including initial-state parton energy loss.

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arXiv2009

Ridge, Bulk, and Medium Response: How to Kill Models and Learn Something in the Process

In these proceedings, we highlight experimental data (published and preliminary) related to jet quenching and the response of the medium to this deposited energy. Signatures in two- and three- particle hadron correlations indicate interesting structures near the trigger particle in azimuth and over a broad range in pseudo-rapidity, often termed "the ridge", and conical-like structures separated in azimuth opposite to the trigger particle. We review numerous theoretical interpretations of the ridge in particular with a critical eye for the key properties that allow one to discriminate between, or rule out, certain physical pictures and models (and hopefully learn something in the process).

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arXiv2009

Quantitative and Conceptual Considerations for Extracting the Knudsen Number in Heavy Ion Collisions

In this paper we examine the methodology for extracting the Knudsen number (K) and the ratio of shear viscosity to entropy density (eta/s) developed by Drescher et al. The final result for eta/s turns out to be quite sensitive to Glauber parameters, and particularly the parameter x which controls the balance between Npart and Ncoll. We also explore how alternative formulations of the functional relation between the elliptic flow and Knudsen number impacts the physics conclusions, based on Pade approximants. Finally, we extend the calculation to include a limiting minimum value on the mean free path proportional to the DeBroglie wavelength. These results emphasize the importance of clarifying the initial state used in different calculations, as well as the ambiguities inherent in using a transport approach in a strongly-coupled regime.

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arXiv2008

The Letter Q (and Quantitative Constraints on the QGP)

In this proceedings, we briefly review the methodology from [arXiv:0801.1665] for quantitatively constraining theoretical model parameters from experimental measurements including statistical and systematic uncertainties. We extend this methodology to additional parton energy-loss calculations for single inclusive high pT particle suppression, and also extend the comparisons to di-jet observations. This is only the start of a process to give quantitative constraints on the quark-gluon plasma, and substantial theoretical uncertainties need to be reduced/resolved in a parallel path.

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arXiv2007

Quasi-Particle Degrees of Freedom versus the Perfect Fluid as Descriptors of the Quark-Gluon Plasma

The hot nuclear matter created at the Relativistic Heavy Ion Collider (RHIC) has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of QCD quasi-particles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy ion collisions. The empirical observation of constituent quark ``$n_q$'' scaling of elliptic flow is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. A ``quasi-particle transport'' time stage after viscous effects break down the hydrodynamic fluid stage, but prior to hadronization, is proposed to reconcile these apparent contradictions. However, without a detailed understanding of the transitions between these stages, the ``$n_q$'' scaling is not a necessary consequence of this prescription. Also, if the duration of this stage is too short, it may not support well defined quasi-particles. By comparing and contrasting the coalescence of quarks into hadrons with the similar process of producing light nuclei from nucleons, it is shown that the observation of ``$n_{q}$'' scaling in the final state does not necessarily imply that the constituent degrees of freedom were the relevant ones in the initial state.

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arXiv2007

Heaviness of Heavy Quarkonia in Heavy Ion Collisions

High energy heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) produce a novel medium characterized by an initial energy density over an order of magnitude above the expected phase transformation value and that then evolves as a nearly inviscid liquid. Probing the medium with auto-generated particles is a key methodology to quantitatively determine the medium properties. Pairs of heavy quarks are an excellent probe since their spatial separation to form various quarkonia states spans the relevant range of color screening lengths in the medium. In this proceedings, we describe results from the PHENIX experiment on $J/ψ$ production and discuss initial physics implications of the measurements.

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arXiv2006

Effects of Multiple Scattering in Cold Nuclear Matter on J/psi Suppression and in Heavy Ion Collisions

Coherent multiple scatterings of c and cbar quark pairs in the environment of heavy ion collisions have been used in a previous work by Qiu et al. [Qiu:1998rz] to study J/psi suppression. That model suggests that heavy quark re-scatterings in a cold nuclear medium can completely explain the centrality dependence of the observed J/psi suppression in Pb+Pb collisions at the SPS [Abreu:2001kd]. Their calculations also revealed significant differences under the assumptions of a color singlet or color octet production mechanism. A more recent analytic calculation [Fujii:2003fq], which includes incoherent final-state re-scatterings with explicit momentum transfer fluctuations in three dimensions, indicates much less suppression and little sensitivity to the production mechanism. In this article, we study simultaneously both the J/psi suppression and p_T modifications, at SPS and RHIC energies. We mainly focus on incoherent momentum transfer fluctuations in two dimensions, which is more appropriate for the heavy-ion collision kinematics. Our analytic and Monte-Carlo calculations reinforce the analytic results in [Fujii:2003fq]. Additionally, we find that the experimental J/psi suppression and from nucleus-nucleus collisions at the SPS or RHIC cannot simultaneously be described in this incoherent multiple scattering framework for any value of the fluctuation strength parameter .

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arXiv2006

The Letter "s" (and the sQGP)

Data from the Relativistic Heavy Ion Collider over the last five years has led many to conclude that the medium created is not the expected quark gluon plasma (QGP), but rather a strongly coupled or strongly interacting quark gluon plasma (sQGP). We explore the meaning of this possible paradigm shift and some of the experimental and theoretical arguments that are associated with it. In this proceedings we detail only a small subset of the relevant issues as discussed at the Hot Quarks 2006 workshop.

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arXiv2005

Heavy Quarks and Heavy Quarkonia as Tests of Thermalization

We present here a brief summary of new results on heavy quarks and heavy quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma Thermalization" Workshop in Vienna, Austria in August 2005, directly following the International Quark Matter Conference in Hungary.

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arXiv2004

Heavy Ion Physics and Quark-Gluon Plasma

These proceedings represent a brief overview of the exciting physics coming out from the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The experimental results from BRAHMS, PHOBOS, PHENIX and STAR indicate a strongly-coupled state of matter that can only be described on the partonic level. Here we review some of the latest experimental results as presented at the meeting of the Division of Particles and Fields of the American Physical Society in Riverside, CA in August 2004.

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arXiv2004

Relativistic Heavy Ion Physics in the New Millennium

The field of relativistic heavy ion physics has seen significant advancement in the new millennium toward a greater understanding of QCD at high temperatures with the commissioning and operation of the Relativistic Heavy Ion Collider. Here we review progress in the field as presented in a set of lectures at the Lake Louise Winter Institute on Fundamental Interactions in February 2004.

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arXiv2003

Conference on the Intersections of Particle and Nuclear Physics 2003: Relativistic Heavy Ion Parallel Session Summary

The Relativistic Heavy Ion Collider (RHIC) came online in 2000, and the last three years have provided a wealth of new experimental data and theoretical work in this new energy frontier for nuclear physics. The transition from quarks and gluons bound into hadrons to a deconfined quark-gluon plasma is expected to occur at these energies, and the effort to understand the time evolution of these complex systems has been significantly advanced. The heavy ion parallel session talks from the Conference on the Intersections of Particle and Nuclear Physics (CIPANP) 2003 are posted at: http://www.phenix.bnl.gov/WWW/publish/nagle/CIPANP/. We provide a brief summary of these sessions here.

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arXiv2003

Heavy Quark Dynamics in Heavy Ion Reactions

Collisions between heavy nuclei at the Relativistic Heavy Ion Collider liberate from the nuclear wavefunction of order 10,000 gluons, quarks and antiquarks. The system is dominated by gluons and up and down (anti) quarks. Heavy quarks, though having little effect on the overall equation of state, are critical as probes of the surrounding medium. We compare predictions from a scenario where the charm quarks escape the medium unaffected and fragment into hadrons in vacuum, and one where the charm quarks are swallowed up by the medium and reflect the overall system hydrodynamics.

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arXiv2002

Does the Charm Flow at RHIC?

Recent PHENIX Au+Au -> e- + X data from open charm decay are shown to be consistent with two extreme opposite dynamical scenarios of ultra-relativistic nuclear reactions. Perturbative QCD without final state interactions was previously shown to be consistent with the data. However, we show that the data are also consistent with zero mean free path hydrodynamics characterized by a common transverse flow velocity field. The surprising coincidence of both D and B hydrodynamic flow spectra with pQCD up to p_T ~ 3 and 5 GeV, respectively, suggests that heavy quarks may be produced essentially at rest in the rapidly expanding gluon plasma. Possible implications and further tests of collective heavy quark dynamics are discussed.

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arXiv2002

A Nuclear Physics Program at the ATLAS Experiment at the CERN Large Hadron Collider

The ATLAS collaboration has significant interest in the physics of ultra-relativistic heavy ion collisions. We submitted a Letter of Intent to the United States Department of Energy in March 2002. The following document is a slightly modified version of that LOI. More details are available at: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/SM/ions

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arXiv2002

Leptonic Observables in Ultra-Relativistic Heavy Ion Collisions

We report on leptonic observables by the PHENIX experiment from data taken during Run II at the Relativistic Heavy Ion Collider (RHIC). We show first results on phi -> K+K-, e+e-, low and intermediate mass dielectron continuum, single electrons from charm, and J/psi yields in proton-proton and Au-Au collisions at sqrt{s_{NN}}=200 GeV.

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