Search

We study diffractive vector meson production at small-$x$ in the collision of electrons and polarized deuterons $e+d^{\uparrow}$. We consider the polarization dependence of the nuclear wave function of the deuteron, which results in an azimuthal angular dependence of the produced vector meson when the deuteron is transversely polarized. The Fourier coefficients extracted from the azimuthal angular dependence of the vector meson differential cross-section exhibit notable differences between longitudinally and transversely polarized deuterons. The angular dependence of the extracted effective deuteron radius provides direct insight into the structure of the polarized deuteron wave function. Furthermore, we observe slightly increased gluon saturation effects when the deuteron is longitudinally polarized compared to the transversely polarized case. The small-$x$ observables studied in this work will be accessible at the future Electron-Ion Collider.

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 $\gamma+p$ 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., Comment: 5 pages, 6 figures. Talk by H.M at DIS2024

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.

We propose new classes of inflation models based on the modular symmetry, where the modulus field $\tau$ serves as the inflaton. We establish a connection between modular inflation and modular stabilization, wherein the modulus field rolls towards a fixed point along the boundary of the fundamental domain. We find the modular symmetry strongly constrain the possible shape of the potential and identify some parameter space where the inflation predictions agree with cosmic microwave background observations. The tensor-to-scalar ratio is predicted to be smaller than $10^{-6}$ in our models, while the running of spectral index is of the the order of $10^{-4}$., Comment: 30 pages, 6 figures, comments are welcomed

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., Comment: 12 pages, 4 figures, 1st International Workshop on the physics of Ultra Peripheral Collisions (UPC 2023)

We present the first study of collectivity inside jets with high charged multiplicity $N^j_{\rm ch}$ in proton-proton collisions at the Large Hadron Collider. By incorporating final-state partonic and hadronic interactions through cascade models among jet shower partons and final hadrons, we investigate and compare to the CMS experimental data on multiplicity distribution, pseudorapidity distribution, and elliptic anisotropy coefficient $v^{j}_2$ of two-particle correlations within the jet. We show that final-state partonic interactions are essential for producing the flow-like long-range correlation, which leads to the enhanced tail in the $N^j_{\rm ch}$ dependence of $v^{j}_2$ above the non-flow correlation from jet parton showering at high multiplicities ($N^j_{\rm ch}\gtrsim70$) as observed in the CMS experimental data. In addition, we provide predictions for the pseudorapidity-gap dependence of $v^{j}_2$ that can be tested in future experimental measurements., Comment: 6 pages, 4 fiures

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., Comment: 62 pages; 9 figures; Contribution to Quark-Gluon Plasma 6 edited by Xin-Nian Wang; v2 matched to the publish version

Considerable information about the early-stage dynamics of heavy-ion collisions is encoded in the rapidity dependence of measurements. To leverage the large amount of experimental data, we perform a systematic analysis using three-dimensional hydrodynamic simulations of multiple collision systems -- large and small, symmetric and asymmetric. Specifically, we perform fully 3D multi-stage hydrodynamic simulations initialized by a parameterized model for rapidity-dependent energy deposition, which we calibrate on the hadron multiplicity and anisotropic flow coefficients. We utilize Bayesian inference to constrain properties of the early- and late- time dynamics of the system, and highlight the impact of enforcing global energy conservation in our 3D model.

Using the Hydro-Coal-Frag model that combines hydrodynamics at low $p_{\rm T}$, quark coalescence at intermediate $p_{\rm T}$, and the LBT transport model at high $p_{\rm T}$, we study the spectra and elliptic flow of identified hadrons in high multiplicity p--Pb and p--p collisions at the Large Hadron Collider (LHC). In p--Pb collisions, the Hydro-Coal-Frag model gives a good description of the differential elliptic flow over the $p_{\rm T}$ range from 0 to 6 GeV and the approximate number of constituent quark (NCQ) scaling at intermediate $p_{\rm T}$. Although Hydro-Coal-Frag model can also roughly describe the elliptic flow in high multiplicity p--p collisions with the quark coalescence process, the larger contribution from the string fragmentations leads to a notable violation of the NCQ scaling of $v_2$ at intermediate $p_{\rm T}$ as observed in the experiment. Comparison runs of the Hydro-Frag model without the coalescence process demonstrate that regardless the parameter adjustments, the Hydro-Frag model cannot simultaneously describe the $p_{\rm T}$ spectra and the elliptic flow of identified hadrons in either p--Pb collisions or p--p collisions. The calculations in this paper thus provide support for the existence of partonic degrees of freedom and the possible formation of the QGP in the small systems created at the LHC., Comment: 9 pages, 3 figures

Within a (3+1)D viscous hydrodynamic model we compute anisotropic flow in small system collisions as performed at the Relativistic Heavy Ion Collider and measured by the STAR and PHENIX Collaborations. We emphasize the importance of the rapidity dependence of the geometry for interpreting the differences encountered in measurements by the two collaborations., Comment: 4 pages; 2 figures; Conference proceedings for Quark Matter 2023, Sept 2023, Houston, Texas, USA

This proceeding highlights the effects of pseudorapidity-dependent charged hadron observables $dN^\mathrm{ch}/d\eta$ and $v_2^{\rm ch}(\eta)$ in Au+Au collisions at 200 GeV on constraining the initial-state nuclear stopping for the beam remnants and the effective QGP specific shear viscosity in a recent Bayesian inference analysis using an event-by-event (3+1)D hydrodynamics + hadronic transport theoretical framework., Comment: 4 pages; 1 figure; Conference proceedings for Quark Matter 2023, Sept 2023, Houston, Texas, USA

Within the Color Glass Condensate framework, we demonstrate that exclusive vector meson production at high energy is sensitive to the geometric deformation of the target nucleus and subnucleon scale fluctuations. Deformation of the nucleus enhances the incoherent cross section in the small $|t|$ region. Subnucleon scale fluctuations increase the incoherent cross section in the large $|t|$ region. In ultra-peripheral collisions (UPCs), larger deformation leads to a wider distribution of the minimal impact parameter $B_{min}$ required to produce a UPC. This, together with larger incoherent cross sections for larger deformation, results in smaller extracted radii. Our results demonstrate great potential for future studies of nuclear structure in UPCs and electron-ion collisions., Comment: 4 pages, proceedings of Quark Matter 2023

In this talk we review jet production in a large variety of collision systems using the JETSCAPE event generator and Hybrid Hadronization. Hybrid Hadronization combines quark recombination, applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems. It can therefore smoothly describe the transition from very dilute parton systems like $e^++e^-$ to full $A+A$ collisions. We test this picture by using JETSCAPE to generate jets in various systems. Comparison to experimental data in $e^++e^-$ and $p+p$ collisions allows for a precise tuning of vacuum baseline parameters in JETSCAPE and Hybrid Hadronization. Proceeding to systems with jets embedded in a medium, we study in-medium hadronization for jet showers. We quantify the effects of an ambient medium, focusing in particular on the dependence on the collective flow and size of the medium. Our results clarify the effects we expect from in-medium hadronization of jets on observables like fragmentation functions, hadron chemistry and jet shape., Comment: 6 pages, 4 figures, Hard Probes 2023 conference, accepted for publication in Proceedings of Science: version 2, references added, typos fixed

We study diffractive vector meson production in ultra-peripheral collisions (UPCs) of heavy nuclei, utilizing a theoretical framework based on the Color Glass Condensate (CGC) formalism. We focus on Au+Au, U+U, Ru+Ru, Zr+Zr, and Pb+Pb collisions, examining the transverse momentum dependence of vector meson production cross-sections and ${\rm cos(2\Delta\Phi)}$ asymmetries in the decay product distributions to explore the role of nuclear geometry. The angular modulation is due to the linear polarization of the incoming photons and quantum interference effects. We extract nuclear radii and find them to be consistent with experimental data from the STAR collaboration. The amplitudes of the ${\rm cos(2\Delta\Phi)}$ modulation in the cross-section and the extracted radii depend on the nuclear geometry. This dependence is dominated by the geometry-dependent variation of the minimum impact parameter required for ultra-peripheral collisions.

This work presents the first Bayesian inference study of the (3+1)D dynamics of relativistic heavy-ion collisions and Quark-Gluon Plasma (QGP) viscosities using an event-by-event (3+1)D hydrodynamics + hadronic transport theoretical framework and data from the Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan program. Robust constraints on initial state nuclear stopping and the baryon chemical potential-dependent shear viscosity of the produced quantum chromodynamic (QCD) matter are obtained. The specific bulk viscosity of the QCD matter is found to exhibit a preferred maximum around $\sqrt{s_\mathrm{NN}} = 19.6$ GeV. This result allows for the alternative interpretation of a reduction (and/or increase) of the speed of sound relative to that of the employed lattice-QCD based equation of state (EOS) for net baryon chemical potential $\mu_B \sim 0.2\, (0.4)$ GeV., Comment: 5 pages, 3 figures

In this article, we consider a class of the contact discontinuity for the full compressible Euler equations, namely the entropy wave, where the velocity is continuous across the interface while the density and the entropy can have jumps. The nonlinear stability of entropy waves is a longstanding open problem in multi-dimensional hyperbolic conservation laws. The rigorous treatments are challenging due to the characteristic discontinuity nature of the problem (G.-Q. Chen and Y.-G. Wang in \textit{Nonlinear partial differential equations}, Volume 7 of \textit{Abel Symp.}(2012)). In this article, we discover that the Taylor sign condition plays an essential role in the nonlinear stability of entropy waves. By deriving the evolution equation of the interface in the Eulerian coordinates, we relate the Taylor sign condition to the hyperbolicity of this evolution equation, which reveals a stability condition of the entropy wave. With the optimal regularity estimates of the interface, we can derive the a priori estimates without loss of regularity., Comment: 23 pages. One appendix deleted. All comments are welcome

Understanding the modification of jets and high-$p_T$ probes in small systems requires the integration of soft and hard physics. We present recent developments in extending the JETSCAPE framework to build an event generator, which includes correlations between soft and hard partons, to study jet observables in small systems. The multi-scale physics of the collision is separated into different stages. Hard scatterings are first sampled at binary collision positions provided by the Glauber geometry. They are then propagated backward in space-time following an initial-state shower to obtain the initiating partons' energies and momenta before the collision. These energies and momenta are then subtracted from the incoming colliding nucleons for soft-particle production, modeled by the 3D-Glauber + hydrodynamics + hadronic transport framework. This new hybrid approach (X-SCAPE) includes non-trivial correlations between jet and soft particle productions in small systems. We calibrate this framework with the final state hadrons' $p_T$-spectra from low to high $p_T$ in $p$-$p$, and and then compare with the spectra in $p$-$Pb$ collisions from the LHC. We also present results for additional observables such as the distributions of event activity as a function of the hardest jet $p_T$ in forward and mid-rapidity for both $p$-$p$ and $p$-$Pb$ collisions., Comment: 6 pages, 6 figures, Proceedings of Hard Probes 2023, 26-31 March 2023 Aschaffenburg, Germany

We show within the Color Glass Condensate framework that exclusive vector meson production at high energy is sensitive to the geometric deformation of the target nucleus at multiple length scales. Studying $e+$U collisions and varying the deformation of the uranium target, we demonstrate that larger deformations result in enhanced incoherent vector meson production cross sections. Further, different multipole deformation parameters affect different regions of transverse momentum transfer. Employing JIMWLK evolution to study the Bjorken-$x$ dependence of our results, we find that the ratio of incoherent to coherent cross sections decreases with decreasing $x$, largely independently of the quadrupole deformation of the target. Comparing results for the same process using ${\rm {^{20}Ne}}$ targets with ${\rm {^{16}O}}$ targets, we find that differences in deformation are clearly visible in the incoherent cross section. These findings show that certain observables at the Electron-Ion Collider are very sensitive to nuclear structure. Consequently, deformations need to be taken into account when interpreting experimental results. More importantly, this also means that $\vert t\vert$-differential diffractive vector meson production could become a powerful tool, enabling the most direct measurements of nuclear structure at different length scales, ranging from nuclear deformation at low $\vert t\vert$ to nucleon- and subnucleon-size scales at higher $\vert t\vert$.

We present (3+1)D dynamical simulations of asymmetric nuclear collisions at the Relativistic Heavy Ion Collider (RHIC). Employing a dynamical initial state model coupled to (3+1)D viscous relativistic hydrodynamics, we explore the rapidity dependence of anisotropic flow in the RHIC small system scan at 200 GeV center of mass energy. We calibrate parameters to describe central $^3$He+Au collisions and make extrapolations to d+Au and p+Au collisions. Our calculations demonstrate that approximately 50% of the $v_3(p_T)$ difference between the measurements by the STAR and PHENIX Collaborations can be explained by the use of reference flow vectors from different rapidity regions. This emphasizes the importance of longitudinal flow decorrelation for anisotropic flow measurements in asymmetric nuclear collisions, and the need for (3+1)D simulations. We also present results for the beam energy dependence of particle spectra and anisotropic flow in d+Au collisions., Comment: Include the STAR new data, and include the statistical error and systematic error

We present full (3+1)D dynamical simulations to study collective behavior in ultra-peripheral nucleus-nucleus collisions (UPC) at the Large Hadron Collider (LHC) with the 3DGlauber+MUSIC+UrQMD framework. By extrapolating from asymmetric p+Pb collisions, we simulate a quasi-real photon $\gamma^*$ interacting with the Pb nucleus in an ultra-peripheral collision at the LHC, assuming strong final-state effects. We study the elliptic flow hierarchy between p+Pb and $\gamma^*$+Pb collisions, which is dominated by the difference in longitudinal flow decorrelations. Our theoretical framework provides a quantitative tool to study collectivity in small asymmetric collision systems at current and future collider experiments., Comment: 4 pages, 2 figures, Conference Proceedings for Strangeness in Quark Matter 2022

The transverse momentum $j_{\rm T}$-dependent jet fragmentation functions have been investigated in proton+proton (p $+$ p) and proton+lead (p $+$ Pb) collisions at $\sqrt{s_{\rm NN}} = 5.02~{\rm TeV}$ with a multiphase transport model containing both a simple quark coalescence mechanism and a new hybrid hadronization mechanism with coalescence and fragmentation processes. Hadronized by the new hadronization mechanism, the AMPT model achieves a quantitative description of the $j_{\rm T}$-dependent jet fragmentation functions measured by ALICE. Besides, no obvious jet-medium interaction and cold nuclear matter effects on the $j_{\rm T}$-dependent jet fragmentation functions in p $+$ Pb collisions were observed. We found the $j_{\rm T}$-dependent jet fragmentation functions are dominated by the quark coalescence contribution for the new hadronization mechanism, which can be decomposed into narrow and wide parts. The root mean square value of the wide part depends on the jet radius $R$ and jet transverse momentum $p_{\rm{T, jet}}$, which is sensitive to different hadronization mechanisms and their components. Therefore, the $j_{\rm T}$-dependent jet fragmentation functions are proposed as a sensitive probe to study the non-perturbative hadronization effect of jets in small colliding systems., Comment: 12 pages, 12 figures, final published version

We determine the likelihood distribution for the model parameters describing the event-by-event fluctuating proton geometry at small $x$ by performing a Bayesian analysis within the Color Glass Condensate framework. The exclusive $\mathrm{J}/\psi$ production data from HERA is found to constrain the model parameters well, and we demonstrate that complementary constraints can be obtained from simulations of Pb+Pb collisions at the LHC., Comment: 6 pages, contribution to the proceedings of the Quark Matter 2022 conference

We present the first full (3+1)D dynamical simulations of ultra-peripheral Pb+Pb collisions at the Large Hadron Collider. Extrapolating from p+Pb collisions, we explore whether a quasi-real photon $\gamma^*$ interacting with the lead nucleus in an ultra-peripheral collision can create a many-body system exhibiting fluid behavior. Assuming strong final-state interactions, we provide model results for charged hadron multiplicity, identified particle mean transverse momenta, and charged hadron anisotropic flow coefficients, and compare them with experimental data from the ALICE and ATLAS collaborations. The elliptic flow hierarchy between p+Pb and $\gamma^*$+Pb collisions is dominated by the difference in longitudinal flow decorrelations and reproduces the experimental data well. We have demonstrated that our theoretical framework provides a quantitative tool to study particle production and collectivity for all system sizes, ranging from central heavy-ion collisions to small asymmetric collision systems at the Relativistic Heavy-Ion Collider and the Large Hadron Collider and even at the future Electron-Ion Collider.

Using Bayesian inference, we determine probabilistic constraints on the parameters describing the fluctuating structure of protons at high energy. We employ the color glass condensate framework supplemented with a model for the spatial structure of the proton, along with experimental data from the ZEUS and H1 Collaborations on coherent and incoherent diffractive $\mathrm{J}/\psi$ production in e+p collisions at HERA. This data is found to constrain most model parameters well. This work sets the stage for future global analyses, including experimental data from e+p, p+p, and p+A collisions, to constrain the fluctuating structure of nucleons along with properties of the final state., Comment: 12 pages, 2 figures. 1000 parameterizations sampled from the determined posterior distributions are included in the source package

Using the AMPT + MUSIC+UrQMD hybrid model, we study the global and local spin polarizations of $\Lambda$ hyperons as functions of the freeze-out temperature of the spin degree of freedom in the hadronic phase of Au+Au collisions at $\sqrt{s_{NN}}=19.6$ GeV. Including contributions from both the thermal vorticity and thermal shear of the hadronic matter, we find that, with the spin freeze-out temperature dropping from the hadronization temperature of 160 MeV to 110 MeV at the kinetic freeze-out, both the global and local spin polarizations of $\Lambda$ hyperons due to the thermal vorticity decrease by a factor of two, while those due to the thermal shear decrease quickly and become negligibly small at 140 MeV. Our results suggest the importance of understanding the dynamical evolution of the spin degree of freedom in the hadronic stage in relativistic heavy-ion collisions., Comment: 5 pages, 3 figures, references updated

Transverse momentum ($p_{T}$) generation in relativistic heavy ion collisions is sensitive to the initial geometry and the final-state bulk evolution. We demonstrate with hydrodynamic calculations that the mean $p_T$ ratio ($R_{\langle p_{T}\rangle}$) between the highly similar isobar $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions is insensitive to the bulk evolution and remains sensitive to the small difference in the initial nuclear structure (neutron skin and deformation) between the Ru and Zr nuclei.We further find that nuclear deformation can produce an anticorrelation between $R_{\langle p_{T}\rangle}$ and eccentricity (or elliptic flow) in central collisions. These findings suggest that the $R_{\langle p_{T}\rangle}$ between the isobar systems can be used to measure the neutron skin thickness and deformation parameters, which can in turn constrain the nuclear symmetry energy slope parameter., Comment: 6 pages, 5 figures