arXiv subjects

James Daniel Brandenburg

Publications and source records attributed to James Daniel Brandenburg.

14 recordsLinked to original sources

arXiv2026

Spin-Selective Hadron Spectroscopy via Azimuthal Anisotropies from Entanglement-Enabled Spin Interference

The $π^+π^-$ invariant mass spectrum above the $ρ^0(770)$ is rich with broad, overlapping resonances. Disentangling them, whether in photoproduction, ultra-peripheral heavy-ion collisions, or electroproduction, is a longstanding challenge for conventional partial-wave analysis. We show that the recently observed entanglement-enabled spin-interference effect in ultra-peripheral collisions provides a quantum-mechanical filter that resolves this ambiguity: the angular harmonics $A_n$ of the $\cos(nΔϕ)$ asymmetry, which are governed by selection rules in the spin of the interfering states. Specifically, overlap between two distinct spin-1 amplitudes leads to interference that populate $A_2$ alone, while overlap of a spin-1 amplitude with a spin-2 one generates $A_1$ and $A_3$. Utilizing ALICE data in the $1.0$--$1.4\,\mathrm{GeV} \; c^{-2}$ region, we demonstrate that two physically distinct hypotheses -- an additional spin-1 $ρ'(1450)$ (produced via photonuclear interactions) versus a spin-2 (photon-photon) $f_2(1270)$ state -- fit the invariant mass spectrum equally well but predict different $A_n$: identically zero $A_1$ and $A_3$ in the spin-1 case, versus pronounced peaks in the spin-2 case. This selection rule provides a new tool for hadronic spectroscopy in ultra-peripheral collisions and the first viable route to isolating the $γγ\toπ^+π^-$ continuum from the dominant photonuclear background, revealing a clean low-energy probe of non-perturbative QCD.

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arXiv2025

Probing Quantum Phenomena through Photoproduction in Relativistic Heavy-Ion Collisions

Photoproduction in ultra-peripheral relativistic heavy-ion collisions displays many unique features, often involving quantum mechanical coherence and two-source interference between photon emission from the two ions. We review the recent experimental results from RHIC and the LHC and theoretical studies of coherent vector meson photoproduction, emphasizing the quantum mechanical aspects of the interactions and the entanglement between the final state particles. These studies enrich our understanding of non-local realism, underscore the critical role of the polarization of the photon source, quantum interference and nuclear effect on the gluon distribution. It paves a way for quantitatively probing the quantum nature of these high-energy nuclear collisions.

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arXiv2024

Imaging the initial condition of heavy-ion collisions and nuclear structure across the nuclide chart

High-energy nuclear collisions encompass three key stages: the structure of the colliding nuclei informed by low-energy nuclear physics, the initial condition (IC) leading to the formation of quark-gluon plasma (QGP), and the hydrodynamic expansion and hadronization of the QGP leading to final-state hadrons observed experimentally. Recent advances in experimental and theoretical methods have ushered in a precision era, enabling an increasingly accurate understanding of these stages. However, most approaches involve simultaneously determining both QGP properties and initial conditions from a single collision system, creating complexity due to the coupled contributions of various stages to the final-state observables. To avoid this, we propose leveraging known knowledge of low-energy nuclear structure and hydrodynamic observables to constrain the IC independently. By conducting comparative studies of collisions involving isobar-like nuclei - species with similar mass numbers but different structures - we disentangle the initial condition's impacts from the QGP properties. This approach not only refines our understanding of the IC but also turns high-energy experiments into a precision tool for imaging nuclear structures, offering insights that complement traditional low-energy approaches. Opportunities for carrying out such comparative experiments at the LHC and other facilities could significantly advance both high-energy and low-energy nuclear physics. Additionally, this approach has implications for the future EIC. While the possibilities are extensive, we focus on selected proposals that could benefit both the high-energy and low-energy nuclear physics communities. Originally prepared as input for the long-range plan of U.S. nuclear physics, this white paper reflects the status as of September 2022, with a brief update on developments since then.

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arXiv2024

Entanglement Enabled Intensity Interferometry in ultrarelativistic ultraperipheral nuclear collisions

An important tool in studying the sub-femtoscale spacetime structure of matter in ultrarelativistic heavy-ion collisions is Hanbury-Brown-Twiss (HBT) intensity interferometry of identical particles in the final state of such collisions. We show here that a variant of an entanglement enabled intensity interferometry ($E^2 I^2$) proposed by Cotler and Wilczek provides a powerful alternative to HBT interferometry in extracting fundamental nonperturbative features of QCD at high energies. In particular, we show that the spatial distributions of color singlet (pomeron) configurations in nuclei can be obtained from exclusive resonant decays of $ρ$-mesons into $π^\pm$-pairs in ultrarelativistic ultraperipheral nuclear collisions (UPCs) at RHIC and the LHC. The $E^2 I^2$ framework developed here is quite general. It can be employed to extract information on the spin structure of pomeron couplings as well as enhance the discovery potential for rare odderon configurations from exclusive vector meson decays into few-particle final states both in UPCs and at the Electron-Ion Collider.

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arXiv2024

Search for baryon junctions in photonuclear processes and isobar collisions at RHIC

During the early development of Quantum Chromodynamics, it was proposed that baryon number could be carried by a non-perturbative Y-shaped topology of gluon fields, called the gluon junction, rather than by the valence quarks as in the QCD standard model. A puzzling feature of ultra-relativistic nucleus-nucleus collisions is the apparent substantial baryon excess in the midrapidity region that could not be adequately accounted for in most conventional models of quark and diquark transport. The transport of baryonic gluon junctions is predicted to lead to a characteristic exponential distribution of net-baryon density with rapidity and could resolve the puzzle. In this context we point out that the rapidity density of net-baryons near midrapidity indeed follows an exponential distribution with a slope of $-0.61\pm0.03$ as a function of beam rapidity in the existing global data from A+A collisions at AGS, SPS and RHIC energies. To further test if quarks or gluon junctions carry the baryon quantum number, we propose to study the absolute magnitude of the baryon vs. charge stopping in isobar collisions at RHIC. We also argue that semi-inclusive photon-induced processes ($γ+p$/A) at RHIC kinematics provide an opportunity to search for the signatures of the baryon junction and to shed light onto the mechanisms of observed baryon excess in the mid-rapidity region in ultra-relativistic nucleus-nucleus collisions. Such measurements can be further validated in A+A collisions at the LHC and $e+p$/A collisions at the EIC.

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arXiv2023

Energy Dependence of the Breit-Wheeler process in Heavy-Ion Collisions and its Application to Nuclear Charge Radius Measurements

The collision energy dependence of the cross section and the transverse momentum distribution of dielectrons from the Breit-Wheeler process in heavy-ion collisions are computed in the lowest-order QED and found to be sensitive to the nuclear charge distribution and the infrared-divergence of the ultra-Lorentz boosted Coulomb field. Within a given experimental kinematic acceptance, the cross section is found to increase while the pair transverse momentum ($\sqrt{\langle p_{T}^{2} \rangle}$) decreases with increasing beam energy. We demonstrate that the transverse-momentum component of Weizsacker-Williams photons is due to the finite extent of the charge source and electric field component in the longitudinal direction. We further clarify the connection between the nuclear charge distribution and the kinematics of produced $e^+e^-$ from the Breit-Wheeler process, and propose a criterion for the validity of the Breit-Wheeler process in relativistic heavy-ion collisions. Following this approach we demonstrate that the experimental measurements of the Breit-Wheeler process in ultra-relativistic heavy-ion collisions can be used to quantitatively constrain the nuclear charge radius. The extracted parameters show sensitivity to the impact parameter dependence, and can be used to study the initial-state and final-state effects in hadronic interactions.

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arXiv2022

Search for Dark Photons in $γγ\rightarrow e^+e^-$ at RHIC

The fundamental nature of Dark Matter remains one of the major mysteries of modern physics. Some models postulate the existence of a massive gauge boson, a "dark photon" ($A^\prime$), that may allow Dark Matter particles to interact with Standard Model particles. Ultra-relativistic heavy-ion collisions produce highly Lorentz-contracted electromagnetic fields with sufficient energy density to potentially manifest as light dark photons. We report limits on dark photon parameters via a search for anomalous production of $e^+e^-$ pairs in $γA^\prime$ and $A^\prime A^\prime$ fusion from ultra-peripheral $\rm{Au}+\rm{Au}$ collisions. This study utilizes measurements of the Breit-Wheeler process ($γγ\rightarrow e^+e^-$) carried out by STAR, specifically making use of polarization-dependent final-state azimuthal asymmetries in $e^+e^-$ pairs. These limits are informative for future searches in the ultra-peripheral heavy-ion collisions and to constrain future theoretical developments of the dark photon mechanism.

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arXiv2022

Report on Progress in Physics: Observation of the Breit-Wheeler Process and Vacuum Birefringence in Heavy-Ion Collisions

This Report reviews the effort over several decades to observe the linear Breit-Wheeler process ($γγ\rightarrow e^+e^-$) and vacuum birefringence in high-energy particle and heavy-ion collider experiment. This Report, motivated by STAR's recent observations, attempts to summarize the key issues related to the interpretation of polarized $γγ\rightarrow l^+l^-$ measurements in high-energy experiments. To that end, we start by reviewing the historical context and essential theoretical developments, before focusing on the decades of progress made in high-energy collider experiments. Special attention is given to the evolution in experimental approaches in response to various challenges and the demanding detector capabilities required to unambiguously identify the linear Breit-Wheeler process and to detect the signatures of vacuum birefringence. We close the report with a discussion, followed by a look at near-future opportunities for utilizing these discoveries and for testing QED in previously unexplored regimes.

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arXiv2022

Exploring gluon tomography with polarization dependent diffractive J/$ψ$ production

We study azimuthal asymmetries in diffractive J/$ψ$ production in ultraperipheral heavy-ion collisions at RHIC and LHC energies using the color glass condensate effective theory. Our calculation successfully describes azimuthal averaged $J/ψ$ production cross section measured by STAR and ALICE. We further predict very large $\cos 2ϕ$ and $\cos 4ϕ$ azimuthal asymmetries for diffractive $J/ψ$ production both in UPCs at RHIC and LHC energies and in eA collisions at EIC energy. These novel polarization dependent observables may provide complementary information for constraining gluon transverse spatial distribution inside large nuclei. As compared to all previous analysis of diffractive $J/ψ$ production, the essential new elements integrated in our theoretical calculations are: the double-slit interference effect, the linear polarization of coherent photons, and the final state soft photon radiation effect.

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arXiv2021

Mapping the Electromagnetic Fields of Heavy-Ion Collisions with the Breit-Wheeler Process

Ultra-relativistic heavy-ion collisions are expected to produce the strongest electromagnetic fields in the known Universe. These highly-Lorentz contracted fields can manifest themselves as linearly polarized quasi-real photons that can interact via the Breit-Wheeler process to produce lepton anti-lepton pairs. The energy and momentum distribution of the produced dileptons carry information about the strength and spatial distribution of the colliding fields. Recently it has been demonstrated that photons from these fields can interact even in heavy-ion collisions with hadronic overlap, providing a purely electromagnetic probe of the produced medium. In this review we discuss the recent theoretical progress and experimental advances for mapping the ultra-strong electromagnetic fields produced in heavy-ion collisions via measurement of the Breit-Wheeler process.

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arXiv2020

New opportunities at the photon energy frontier

Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the energy frontier for photon-mediated interactions. UPC photons can be used for many purposes, including probing low-$x$ gluons via photoproduction of dijets and vector mesons, probes of beyond-standard-model processes, such as those enabled by light-by-light scattering, and studies of two-photon production of the Higgs.

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arXiv2020

Exploring the double-slit interference with linearly polarized photons

The linearly polarized quasi-real photons from the highly Lorentz-contracted Coulomb fields of relativistic heavy ions can fluctuate to quark-antiquark pairs, scatter off a target nucleus and emerge as vector mesons. In the process, the two colliding nuclei can switch roles to act as photon emitter or target, forming a double-slit interference pattern. The product from photoproduction inherits the photon polarization states, leading to the asymmetries of the decay angular distributions. In this letter, we study the interference effect in polarization dimension from the asymmetries of the decay angular distributions for photoprodution in heavy-ion collisions and find a periodic oscillation with the transverse momentum of vector meson, which could reasonably explain the transverse momentum dependence of the 2nd-order modulation in azimuth for the $ρ^{0}$ decay observed by the STAR collaboration.

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arXiv2020

Acoplanarity of QED pairs accompanied by nuclear dissociation in ultra-peripheral heavy ion collisions

This paper investigates the transverse momentum broadening effect for electromagnetic production of dileptons in ultra-peripheral heavy ion collisions accompanied by nuclear dissociation. The electromagnetic dissociation probability of nuclei for different neutron multiplicities is estimated, which could serve as a centrality definition (i.e. impact parameter estimate) in ultra-peripheral collisions. In the framework of lowest-order QED, the acoplanarity of dilepton pairs is calculated for different neutron emission scenarios in ultra-peripheral collisions, indicating significant impact-parameter dependence. The verification of impact-parameter dependence is crucially important to understand the broadening effect observed in hadronic heavy-ion collisions.

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arXiv2019

Initial transverse-momentum broadening of Breit-Wheeler process in relativistic heavy-ion collisions

We calculate the cross section and transverse-momentum ($P_{\bot}$) distribution of the Breit-Wheeler process in relativistic heavy-ion collisions and their dependence on collision impact parameter ($b$). To accomplish this, the Equivalent Photon Approximation (EPA) was generalized in a more differential way compared to the approach traditionally used for inclusive collisions. In addition, a lowest-order QED calculation with straightline assumption was performed as a standard baseline for comparison. The cross section as a function of $b$ is consistent with previous calculations using the equivalent one-photon distribution function. Most importantly, the $P_{\bot}$ shape from this model is strongly dependent on impact parameter and can quantitatively explain the $P_{\bot}$ broadening observed recently by RHIC and LHC experiments. This broadening effect from the initial QED field strength should be considered in studying possible trapped magnetic field and multiple scattering in a Quark-Gluon Plasma (QGP). The impact-parameter sensitive observable also provides a controllable tool for studying extreme electromagnetic fields.

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