arXiv subjects

Björn Schenke

Publications and source records attributed to Björn Schenke.

At least 37 records · Page 2Linked to original sources

arXiv2025

Nuclear Physics Confronts Relativistic Collisions Of Isobars

High-energy collisions involving the $A=96$ isobars $^{96}$Zr and $^{96}$Ru have been performed in 2018 at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) as a means to search for the chiral magnetic effect in QCD. This would manifest itself as specific deviations from unity in the ratio of observables taken between $^{96}$Zr+$^{96}$Zr and $^{96}$Ru+$^{96}$Ru collisions. Measurements of such ratios (released at the end of 2021) indeed reveal deviations from unity, but these are primarily caused by the two collided isobars having different radial profiles and intrinsic deformations. To make progress in understanding RHIC data, nuclear physicists across the energy spectrum gathered in Heidelberg in 2022 as part of an EMMI Rapid Reaction Task Force (RRTF) to address the following question. Does the combined effort of low-energy nuclear structure physics and high-energy heavy-ion physics enable us to understand the observations made in isobar collisions at RHIC?

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arXiv2025

Finite-size effects on small-$x$ evolution and saturation in proton and nuclear targets

Within the Color Glass Condensate effective field theory, we assess the importance of including a finite size for the target on observables sensitive to small-$x$ evolution. To this end, we study the Balitsky-Kovchegov (BK) equation with impact-parameter dependence in the initial condition. We demonstrate that neglecting the dependence on the impact parameter can result in overestimated saturation effects for protons, while it has little effect for heavy nuclei at the energies available at current experiments. When fixing the nonperturbative parameters to the energy dependence of the exclusive $J/ψ$ photoproduction cross section with proton targets, predictions for lead targets are not sensitive to the applied running-coupling prescription, the scheme chosen to resum large transverse logarithms in the BK equation, or the infrared regulator in the evolution.

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arXiv2025

Four-dimensional QCD equation of state at finite chemical potentials

Exploration of the QCD phase diagram is pivotal in particle and nuclear physics. We construct a full four-dimensional equation of state of QCD with net baryon, electric charge, and strangeness by extending the NEOS model beyond the conventional two-dimensional approximation. Lattice QCD calculations based on the Taylor expansion method and the hadron resonance gas model are considered for the construction. We also develop an efficient numerical method for applying the four-dimensional equation of state to relativistic hydrodynamic simulations, which can be used for the analysis of nuclear collisions at beam energy scan energies and for different nuclear species at the BNL Relativistic Heavy Ion Collider.

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arXiv2025

Anisotropic flow in fixed-target $^{208}$Pb+$^{20}$Ne collisions as a probe of quark-gluon plasma

The System for Measuring Overlap with Gas (SMOG2) at the LHCb detector enables the study of fixed-target ion-ion collisions at relativistic energies ($\sqrt{s_{\rm NN}}\sim100$ GeV in the centre-of-mass). With input from \textit{ab initio} calculations of the structure of $^{16}$O and $^{20}$Ne, we compute 3+1D hydrodynamic predictions for the anisotropic flow of Pb+Ne and Pb+O collisions, to be tested with upcoming LHCb data. This will allow the detailed study of quark-gluon plasma (QGP) formation as well as experimental tests of the predicted nuclear shapes. Elliptic flow ($v_2$) in Pb+Ne collisions is greatly enhanced compared to the Pb+O baseline due to the shape of $^{20}$Ne, which is deformed in a bowling-pin geometry. Owing to the large $^{208}$Pb radius, this effect is seen in a broad centrality range, a unique feature of this collision configuration. Larger elliptic flow further enhances the quadrangular flow ($v_4$) of Pb+Ne collisions via non-linear coupling, and impacts the sign of the kurtosis of the elliptic flow vector distribution ($c_2\{4\}$). Exploiting the shape of $^{20}$Ne proves thus an ideal method to investigate the formation of QGP in fixed-target experiments at LHCb, and demonstrates the power of SMOG2 as a tool to image nuclear ground states.

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arXiv2025

Collision energy dependence in heavy ion collisions from nonlinear QCD evolution

We explore the effects of including the energy dependence determined from evolution equations within the color glass condensate framework on observables in ultra-relativistic heavy-ion collisions. This amounts to integrating the JIMWLK evolution equations into the IP-Glasma model, which is then coupled to viscous relativistic hydrodynamics. This methodology allows for a systematic representation of nuclei at specific Bjorken-$x$ values, which are probed at different center-of-mass energies of the collision and rapidities of final state particles. Comparing to the conventional IP-Glasma model, we find significant effects on multiplicity distributions and particle spectra, especially in smaller collision systems at the highest center of mass energies. Our results highlight the importance of incorporating nonlinear QCD evolution in the description of heavy ion collisions at varying center of mass energies, as the precise extraction of transport coefficients will be affected. This work establishes a robust framework for understanding the quark gluon plasma and nuclear structure at high energy, integrating small-$x$ physics into the initial conditions of heavy-ion collisions.

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arXiv2024

Hydrodynamic Description of the Quark-Gluon Plasma

We review the history and success of applying relativistic hydrodynamics to high-energy heavy-ion collisions. We emphasize the important role hydrodynamics has played in the discovery of the quark-gluon plasma and its quantitative exploration.

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arXiv2024

Collectivity in ultra-peripheral heavy-ion and e+A collisions

We review recent theoretical progress in describing collective effects in photon+nucleus collisions. The approaches considered range from the color glass condensate where correlations are encoded in the initial state, to hydrodynamic frameworks, where a strong final state response to the initial geometry of the collision is the key ingredient to generate momentum-space correlations.

hep-ph↗

arXiv2024

Four-dimensional QCD equation of state with multiple chemical potentials

We construct a four-dimensional version of the equation of state (EoS) model NEOS, NEOS-4D, as a function of the temperature and chemical potentials of baryon, electric charge, and strangeness for the hot and dense QCD matter created in relativistic nuclear collisions. This EoS enables multiple conserved charge current evolution in a relativistic fluid. Input from Lattice QCD simulations and a hadron resonance gas model is considered for constructing the equation of state. We investigate its applicability to the relativistic hydrodynamic description of nuclear collisions and present a method for efficient numerical implementation.

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arXiv2024

Probing Nuclear Structure of Heavy Ions at the Large Hadron Collider

We perform high-statistics simulations to study the impacts of nuclear structure on the ratios of anisotropic flow observables in $^{208}$Pb+$^{208}$Pb and $^{129}$Xe+$^{129}$Xe collisions at the Large Hadron Collider. Even with $40\%$ difference in atomic numbers between $^{208}$Pb and $^{129}$Xe nuclei, the ratios of anisotropic flow in the same centrality class between the two collision systems are strongly affected by the nuclear structure inputs in the initial state. The ratios of $v_2\{4\}/v_2\{2\}$ in these collisions are sensitive to the nuclear skin thickness of the colliding nuclei, providing indirect constraints on the nuclei's neutron skin. Our model predictions serve as a benchmark to compare with experimental measurements.

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arXiv2024

Simulating Charm Quarks in IP-Glasma Initial Stage and Quark-Gluon Plasma: A Hybrid Approach for charm quark phenomenology

We present phenomenological findings on charm quark transport while including its energy loss in both pre-equilibrium and hydrodynamic stages of the evolution. We employed the MARTINI event generator for the production and evolution of heavy quarks in the relativistic heavy-ion collisions. The sensitivity of the heavy meson nuclear modification factor and flow coefficient to the early stage of heavy-ion collisions and bulk medium evolution is analyzed for Pb+Pb collisions at 5.02 TeV. Our study provides insights into the interaction strength of charm quarks during the early phase and within the quark-gluon plasma.

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arXiv2024

Probing gluon saturation and nuclear structure in photon-nucleus collisions

We calculate exclusive vector meson photoproduction within the Color Glass Condensate framework in high-energy photon-nucleus scattering probed experimentally in ultra peripheral heavy ion collisions at RHIC and at the LHC. When the free parameters are constrained by the $γ+p$ data from HERA, we predict significant nuclear suppression for both the coherent and incoherent photoproduction cross section in the TeV range. Our results indicate that the LHC data prefers even stronger saturation effects at the highest collision energies. Furthermore, we demonstrate how the linear polarization of photons in ulra peripheral collisions generates azimuthal modulations in the decay products of the exclusively produced vector meson. We show how these measurements can probe details of the nuclear geometry, specifically the deformed structure of the uranium nuclei.

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arXiv2024

Progress and Challenges in Small Systems

We present a comprehensive review of the theoretical and experimental progress in the investigation of novel high-temperature quantum chromodynamics phenomena in small systems at both the Relativistic Heavy Ion Collider and the Large Hadron Collider. We highlight the challenges and opportunities associated with studying small systems, by which we generally mean collision systems that involve at least one light ion or even a photon projectile. We discuss perspectives on possible future research directions to better understand the underlying physics at work in the collisions of small systems.

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arXiv2024

Unveiling baryon charge carriers through charge stopping in isobar collisions

Utilizing a comprehensive (3+1)D relativistic hydrodynamic framework with multiple conserved charge currents and charge-dependent Lattice-QCD-based equation of state, we study the baryon and electric charge number deposition at mid rapidity in isobar Ru+Ru and Zr+Zr collisions at the center of mass energy $\sqrt{s_\mathrm{NN}}=200$ GeV. Comparing our predictions with upcoming experimental data from the Relativistic Heavy Ion Collider will shed light on the existence of baryon junctions.

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arXiv2024

Gluon imaging using azimuthal correlations in diffractive scattering at the Electron-Ion Collider

We study coherent diffractive photon and vector meson production in electron-proton and electron-nucleus collisions within the Color Glass Condensate effective field theory. We show that electron-photon and electron-vector meson azimuthal angle correlations are sensitive to non-trivial spatial correlations in the gluon distribution of the target, and perform explicit calculations using spatially dependent McLerran-Venugopalan initial color charge configurations coupled to the numerical solution of small $x$ JIMWLK evolution equations. We compute the cross-section differentially in $Q^2$ and $|t|$ and find sizeable anisotropies in the electron-photon and electron-$\mathrm{J}/ψ$ azimuthal correlations ($v_{1,2} \approx 2 - 10 \%$) in electron-proton collisions for the kinematics of the future Electron-Ion Collider. In electron-gold collisions these modulations are found to be significantly smaller ($v_{1,2} <0.1 \%$). We also compute incoherent diffractive production where we find that the azimuthal correlations are sensitive to fluctuations of the gluon distribution in the target.

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arXiv2024

Vector meson production in ultraperipheral heavy ion collisions

We review model calculations of exclusive vector meson production in ultraperipheral heavy ion collisions. We highlight differences and similarities between different dipole models and leading twist shadowing calculations. Recent color glass condensate calculations are presented with focus on effects from nuclear structure and azimuthal anisotropies driven by interference effects.

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arXiv2024

Energy dependent nuclear suppression from gluon saturation in exclusive vector meson production

We calculate the exclusive $\mathrm{J}/ψ$ photoproduction cross section at high energies from the Color Glass Condensate approach. The results are compared to the center-of-mass energy dependent $γ+A\to\mathrm{J}/ψ+A$ cross sections extracted from measurements in ultra peripheral heavy ion collisions at RHIC and LHC. We predict strong saturation-driven nuclear suppression at high energies, while LHC data prefers even stronger suppression. We explore the effect of nucleon shape fluctuations on the nuclear suppression in the coherent and incoherent cross sections, and show that the most recent measurement of the $|t|$-differential incoherent $\mathrm{J}/ψ$ cross section prefers large event-by-event fluctuations of the nucleon substructure in heavy nuclei, comparable to that found for a free proton.

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arXiv2024

Back-to-back inclusive dijets in DIS at small $x$: Complete NLO results and predictions

We compute the back-to-back dijet cross-section in deep inelastic scattering (DIS) at small $x$ to next-to-leading order (NLO) in the Color Glass Condensate effective field theory. Our result can be factorized into a convolution of the Weizsäcker-Williams gluon transverse momentum dependent distribution function (WW gluon TMD) with a universal soft factor and an NLO coefficient function. The soft factor includes both double and single logarithms in the ratio of the relative transverse momentum $P_\perp$ of the dijet pair to the dijet momentum imbalance $q_\perp$; its renormalization group (RG) evolution is resummed into the Sudakov factor. Likewise, the WW TMD obeys a nonlinear RG equation in $x$ that is kinematically constrained to satisfy both lifetime and rapidity ordering of the projectile. Exact analytical expressions are obtained for the NLO coefficient function of transversely and longitudinally polarized photons. Our results allow for the first quantitative separation of the dynamics of Sudakov suppression from that of gluon saturation. They can be extended to other final states and provide a framework for precision tests of novel QCD many-body dynamics at the Electron-Ion Collider.

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arXiv2023

Tracing baryon and electric charge transport in isobar collisions

It is of fundamental interest to understand the carrier of conserved quantum charges within protons and nuclei at high energy. Preliminary data from isobar collisions at RHIC reveal a scaled net-baryon to net-electric charge ratio ($B/ΔQ \times ΔZ/A$) at mid-rapidity between 1.2 and 2, consistent with string junction model predictions. Here, we compute the initial stage scaled net-baryon to net-electric charge ratio for isobar collisions. Our model incorporates a realization of the string junction model and models the nuclear structure. Our predictions identify the baseline expectations for such measurement and quantify the impact of the nuclear structure.

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