arXiv subjects

Christopher Plumberg

Publications and source records attributed to Christopher Plumberg.

34 records · Page 2Linked to original sources

arXiv2021

Charge Balance Functions for Heavy-Ion Collisions at LHC Energies

Heavy-ion collisions at the LHC provide the conditions to investigate regions of quark-gluon plasma that reach higher temperatures and that persist for longer periods of time compared to collisions at the Relativistic Heavy Ion Collider. This extended duration allows correlations from charge conservation to better separate during the quark-gluon plasma phase, and thus be better distinguished from correlations that develop during the hadron phase or during hadronization. In this study charge balance functions binned by relative rapidity and azimuthal angle and indexed by species are considered. A detailed theoretical model that evolves charge correlations throughout the entirety of an event is compared to preliminary results from the ALICE Collaboration. The comparison with experiment provides insight into the evolution of the chemistry and diffusivity during the collision. A ratio of balance functions is proposed to better isolate the effects of diffusion and thus better constrain the diffusivity.

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arXiv2021

$^{16}\mathrm{O}^{16}\mathrm{O}$ at RHIC and the LHC comparing $α$ clustering vs substructure

Collisions of light and heavy nuclei in relativistic heavy-ion collisions have been shown to be sensitive to nuclear structure. With a proposed $^{16}\mathrm{O}^{16}\mathrm{O}$ run at the LHC and RHIC we study the potential for finding $α$ clustering in $^{16}$O. Here we use the state-of-the-art iEBE-VISHNU package with $^{16}$O nucleonic configurations from {\rm ab initio} nuclear lattice simulations. This setup was tuned using a Bayesian analysis on pPb and PbPb systems. We find that the $^{16}\mathrm{O}^{16}\mathrm{O}$ system always begins far from equilibrium and that at LHC and RHIC it approaches the regime of hydrodynamic applicability only at very late times. Finally, by taking ratios of flow harmonics we are able to find measurable differences between $α$-clustering, nucleonic, and subnucleonic degrees of freedom in the initial state.

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arXiv2020

The Multiplicity Dependence of Pion Interferometry in Hydrodynamics

Understanding the origins of collective, fluid-like behavior in ultrarelativistic nuclear collisions constitutes one of the biggest open challenges in the field. In this Letter, it is argued that certain features in the multiplicity dependence of the source sizes extracted using pion interferometry may be understood quite naturally if small systems evolve hydrodynamically at sufficiently large multiplicities. Interferometry may therefore provide a baseline for probing and constraining the nature of collective behavior in nuclear collisions.

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arXiv2020

Hanbury Brown--Twiss Interferometry and Collectivity in Small Systems

Hanbury Brown--Twiss interferometry (HBT) provides crucial insights into both the space-time structure and the momentum-space evolution of ultrarelativistic nuclear collisions at freeze-out. In particular, the dependence of the HBT radii on the transverse pair momentum $K_T$ and the system charged multiplicity $dN_{\mathrm{ch}}/dη$ may reflect the mechanisms driving collective behavior in small systems. This paper argues that certain features observed in the multiplicity dependence of the HBT radii can be naturally understood if small systems evolve hydrodynamically at high-multiplicity. This study thus establishes a baseline for the multiplicity dependence of HBT in hydrodynamics which may prove useful in discriminating between competing models of collectivity in nuclear collisions.

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arXiv2020

Calculating Fluctuations and Self-Correlations Numerically for Causal Charge Diffusion in Relativistic Heavy-Ion Collisions

We study the propagation and diffusion of electric charge fluctuations in the Bjorken hydrodynamic model with both white and Catteneo noise using purely numerical methods. We show that a global lattice of noise fluctuations is required to fully calculate the two-point correlators of charge. We solve the stochastic differential equations that arise from the charge conservation equation on the lattice. We explicitly identify the self-correlation term in the case of Catteneo noise and provide a physical interpretation. We provide a numerical recipe to remove this contribution from the full two-point correlators. Finally, we calculate the balance functions for charged hadrons. By limiting the speed of signal propagation, we observe the expected narrowing of the balance functions after removing the self-correlations.

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arXiv2019

Randall-Sundrum Model with a Dilaton Field at Finite Temperature

We find exact finite temperature solutions to $d=5$ Einstein-dilaton gravity with black branes and a Randall--Sundrum 3-brane. We show that there exists a unique generating superpotential for these models. The location of the black brane and the associated Hawking temperature depend on the value of the the 3-brane tension while other parameters are held fixed. The thermodynamics of these solutions are presented, from which we show that the entropy satisfies $S<\text{Vol}(\mathbb{R}^3)/4G_5$. We demonstrate that in a certain limit the gauge dual of this theory effectively reduces to $\mathcal{N}=4$ SYM at finite temperature on $S^1\times\mathbb{R}^3$

hep-th↗

arXiv2019

The Shape of the Correlation Function

The two-particle correlation function employed in Hanbury-Brown Twiss interferometry and femtoscopy is traditionally parameterized by a Gaussian form. Other forms, however, have also been used, including the somewhat more general Lévy form. Here we consider a variety of effects present in realistic femtoscopic studies which may modify the shape of the correlation function and thereby influence the physical interpretation of a given parameterization.

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arXiv2019

The Shape of the Correlation Function

The correlation function measured in ultrarelativistic nuclear collisions is non-Gaussian. By making use of models we discuss and assess how much various effects can influence its shape. In particular, we focus on the parametrisations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as non-spherical shape, resonance decays, event-by-event fluctuations and functional dependence on $Q_{inv}$ or similar.

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arXiv2018

Evolving Charge Correlations in a Hybrid Model with both Hydrodynamics and Hadronic Boltzmann Descriptions

Correlations related to local charge conservation provide insight into the creation and evolution of up, down and strange charges in the quark-gluon plasma. Here, the evolution of charge correlations is overlaid onto a hydrodynamic calculation for the regions where temperature exceed 155 MeV, then transferred and carried through a microscopic model of the hadronic stage. Thus, for the first time, charge correlations are evolved consistently with a full state-of-the-art description of a heavy-ion collision. The charge correlations are projected onto charge balance functions, which characterize such correlations in the final state, and are presented as a function of relative rapidity and relative azimuthal angle for Au/Au collisions. The role of the hadronic stage is investigated. Calculation of the contribution to charge-separation observables related to the chiral magnetic effect are also presented. Calculations are compared to data from the STAR Collaboration at RHIC (Relativistic Heavy Ion Collider) data when possible.

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arXiv2018

HoTCoffeeh: Hanbury Brown-Twiss correlation functions and radii from event-by-event hydrodynamics

$\textbf{HoTCoffeeh}$ ($\textbf{H}$anbury Br$\textbf{o}$wn-$\textbf{T}$wiss $\textbf{Co}$rrelation $\textbf{f}$unctions and radii $\textbf{f}$rom $\textbf{e}$vent-by-$\textbf{e}$vent $\textbf{h}$ydrodynamics) is a new computational tool which determines Hanbury Brown-Twiss (HBT) charged pion ($π^+$) correlation functions and radii for event-by-event (EBE) hydrodynamics with fluctuating initial conditions in terms of Cooper-Frye integrals, including resonance decay contributions. In this paper, we review the basic formalism for computing the HBT correlation functions and radii with resonance decay contributions included, and discuss our implementation of this formalism in the form of HoTCoffeeh. This tool may be easily integrated with other numerical packages for the purpose of simulating the evolution of heavy-ion collisions and thereby extracting predictions for heavy-ion observables.

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arXiv2017

Causal Electric Charge Diffusion and Balance Functions in Relativistic Heavy Ion Collisions

We study the propogation and diffusion of electric charge fluctuations in high energy heavy ion collisions using the Cattaneo form for the dissipative part of the electric current. As opposed to the ordinary diffusion equation this form limits the speed at which charge can propagate. Including the noise term in the current, which arises uniquely from the fluctuation-dissipation theorem, we calculate the balance functions for charged hadrons in a simple 1+1 dimensional Bjorken hydrodynamical model. Limiting the speed of propagation of charge fluctuations increases the height and reduces the width of these balance functions when plotted versus rapidity. We also estimate the numerical value of the associated diffusion time constant from AdS/CFT theory.

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arXiv2017

Hydrodynamic fluctuations near a critical endpoint and Hanbury Brown-Twiss interferometry

The field of high energy nuclear collisions has witnessed a surge of interest in the role played by hydrodynamic fluctuations. Hydrodynamic fluctuations may have significant effects on matter created in heavy-ion accelerators whose trajectories in the plane of temperature versus chemical potential pass near a possible critical endpoint. We extend previous studies to explore the impact of these fluctuations on Hanbury Brown-Twiss interferometry of identical hadrons. With an appropriately defined correlation function we find that the fluctuations increase substantially when the trajectory passes near a critical endpoint, and also displays a damped oscillatory behavior in the rapidity distance $Δy$ unlike that originating from initial-state fluctuations.

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arXiv2015

Observable consequences of event-by-event fluctuations of HBT radii

We explore the effects of event-by-event fluctuations of Hanbury Brown-Twiss (HBT) radii and show how they can be observed experimentally. The relation of measured HBT radii extracted from ensemble-averaged correlation functions to the mean of their event-by-event probability distribution is clarified. We propose a method to experimentally determine the mean and variance of this distribution and test it on an ensemble of fluctuating events generated with the viscous hydrodynamic code VISH2+1. Using the same code, the sensitivity of the mean and variance of the HBT radii to the specific QGP shear viscosity $η/s$ is studied. We report sensitivity of the mean pion HBT radii and their variances to the temperature dependence of $η/s$ near the quark-hadron transition at a level similar (10-20%) to that which was previously observed for elliptic and quadrangular flow of charged hadrons [1].

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arXiv2015

Probing the properties of event-by-event distributions in Hanbury-Brown--Twiss radii

Hanbury-Brown--Twiss interferometry is a technique which yields effective widths (i.e., "HBT radii") of homogeneity regions in the fireballs produced in heavy ion collisions. Because the initial conditions of these collisions are stochastically fluctuating, the measured HBT radii also exhibit variation on an event-by-event basis. However, HBT measurements have, to date, been performed only on an ensemble-averaged basis, due to inherent limitations of finite particle statistics. In this paper, we show that experimental measurements to date are best characterized theoretically as weighted averages of the event-by-event HBT radii, and we propose a new method for extracting experimentally both the arithmetic mean and the variance of the event-by-event distribution of HBT radii. We demonstrate the extraction of the mean and variance of this distribution for a particular ensemble of numerically generated events, and offer some ideas to extend and generalize the method to enable measurement of higher moments of the HBT distribution as well.

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arXiv2015

Interferometric signatures of the temperature dependence of the specific shear viscosity in heavy-ion collisions

Recent work has shown that a temperature dependence of the shear viscosity to entropy ratio, $η/s$, influences the collective flow pattern in heavy-ion collisions in characteristic ways that can be measured by studying hadron transverse momentum spectra and their anisotropies. Here we point out that it also affects the pair momentum dependence of the Hanbury-Brown$-$Twiss (HBT) radii (the source size parameters extracted from two-particle intensity interferometry) and the variance of their event-by-event fluctuations. This observation establishes interferometric signatures as useful observables to complement the constraining power of single-particle spectra on the temperature dependence of $η/s$.

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arXiv2010

Far Ultraviolet Spectroscopy of Seven Nova-Like Variables

We present the results of a multi-component synthetic spectral analysis of the archival far ultraviolet spectra of several key nova-like variables including members of the SW Sex, RW Tri, UX UMa and VY Scl subclasses: KR Aur, RW Tri, V825 Her, V795 Her, BP Lyn, V425 Cas and HL Aqr. Accretion rates as well as the possible flux contribution of the accreting white dwarf are included in our analysis. Except for RW Tri which has a reliable trigonometric parallax, we computed the distances to the nova-like systems using the method of Knigge (2006). Our analysis of seven archival IUE spectra of RW Tri at its parallax distance of 341 pc consistently indicates a low mass (0.4Msun) white dwarf and an average accretion rate, 6.3 E-9Msun/yr. For KR Aur, we estimate that the white dwarf has Teff=29,000K, log g = 8.4 and contributes 18% of the FUV flux while an accretion disk with accretion rate of 3 E-10Msun/yr at an inclination of 41 degrees, contributes the remainder. We find that an accretion disk dominates the far UV spectrum of V425 Cas but a white dwarf contributes non-negligibly with approximately 18% of the FUV flux. For the two high state nova-likes, HL Aqr and V825 Her, their accretion disks totally dominate with 1 E-9Msun/yr and 3 E-9Msun/yr, respectively. For BP Lyn we find an accretion rate of 1 E-8Msun/yr while for V795 Her, we find an accretion rate of 1 E-10Msun/yr. We discuss the implications of our results for the evolutionary status of nova-like variables.

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