After briefly reviewing recent developments in the field, we show how far-from-equilibrium hydrodynamics may be systematically defined, for arbitrary flow profiles, in terms of a generalized tensorial expansion with transport coefficients that contain an all order resummation in gradients. We discuss how this approach naturally relates to *hydrodynamic attractor* solutions found both at weak...

Electroweak bosons are created in the hard scattering processes at the initial stage of heavy-ion collisions and they are insensitive to the presence of the strongly-interacting medium. This makes them clean probes of the initial-state effects in heavy-ion collisions, such as the nuclear modification of the Parton Distribution Functions (nPDFs). Furthermore, their measurement in heavy-ion...

Electroweak bosons provide a unique opportunity to extract the information about the beginning of the temporal evolution of the heavy-ion collision system and understand how the cold nuclear matter effects influence the observables that are measured in heavy-ion collisions. $Z$ and $W$ bosons decaying in leptonic channels are unaffected by the presence of the quark-gluon plasma and carry the...

We investigate the impact of hydrodynamic fluctuations on correlation functions of a relativistic fluid with a conserved U(1) charge. The kinetic equations for the two-point functions of pressure, momentum and heat energy densities are derived within the framework of stochastic hydrodynamics. The leading non-analytic contributions to the energy-momentum tensor as well as the U(1) current are...

We map the infrared dynamics of a relativistic single component (N=1) interacting scalar field theory to that of nonrelativistic complex scalar fields. The Gross-Pitaevskii (GP) equation, describing the real time dynamics of single component ultracold Bose gases, is obtained at first nontrivial order in an expansion proportional to the powers of λϕ^2/m^2 where λ, ϕ and m are the coupling...

Quarkonia, bound states of either a charm and anti-charm quark pair (e.g. $\rm{J}/\psi$, $\psi$(2S)), or a beauty and anti-beauty charm pair ($\Upsilon$(1S), (2S) and (3S)), are considered a prominent tool to study the properties of the Quark-Gluon Plasma (QGP) formed in high-energy heavy-ion collisions such as those delivered by the LHC. However, their production is also sensitive to so...

In holographic heavy ion collisions it is possible to follow both the energy density and a globally conserved (baryon) number density throughout the evolution, dual to a metric and Maxwell field in the dual bulk theory, respectively. At infinite coupling, past work has shown that after the collision the baryon number ends up around mid-rapidity, which is different from high energy heavy ion...

In this work, we implement an effective kinetic theory based scattering kernel in the anisotropic hydrodynamics (aHydro) formalism. We compare the realistic kernel results to those obtained from aHydro with the Anderson-Witting scattering kernel (RTA). For the purpose of this study, we consider a conformal system undergoing transversally-homogenous and boost-invariant Bjorken expansion. The...

In this talk we present the measurement of the muon pair continuum in p+p and p+Au collisions at a center of mass energy of 200 GeV. Our novel analysis technique enables the isolation of correlated pairs from semi-leptonic decays of charm and bottom hadrons and from the Drell-Yan process. The measured azimuthal correlations of muon pairs from heavy flavor decays are used to constrain the...

A key ingredient to model heavy ion collisions dynamically is the initial spatial distribution of protons and neutrons inside the nucleus. Traditionally in most theoretical calculations there is no difference between them and their positions are sampled with the Woods-Saxon distribution. However, this assumption has been invalidated by experimental measurements [1]: The diffusiveness of the...

Non-equilibrium Green's functions provide an efficient tool to describe the evolution of the energy-momentum tensor during the early time pre-equilibrium stage, and provide a meaningful to address the question when and to what extent a hydrodynamic description of the system becomes applicable. We present a calculation of the Green's functions describing the evolution of energy density...

The elliptic and triangular flow coefficients, $v_{2}$ and $v_{3}$, are expected to be driven by the initial anisotropy coefficients of the same order, $\epsilon_{2}$ and $\epsilon_{3}$, respectively. However, the higher order flow coefficients, $v_{n}$ (n $>$ 3), are comprised of linear contributions driven by $\epsilon_{n}$, as well as mode-coupled contributions derived from the lower order...

Relativistic viscous hydrodynamics has been an essential tool in studying the evolution of the Quark Gluon Plasma (QGP) produced in heavy-ion collisions as well as in searching for the critical point expected to be present for more baryon dense systems. With the coming runs of the Beam Energy Scan II at the Relativistic Heavy Ion Collider (RHIC), it will be necessary to implement conserved...

Various microscopic models suggest that local rest frame momentum anisotropies can be large during the early stages of evolution of the quark-gluon plasma (QGP). In recent years, the framework of relativistic anisotropic hydrodynamics (aHydro) has been developed in order to incorporate momentum anisotropic distributions of the QGP constituents into the phenomenological studies of...

We study the heavy-quark momentum diffusion coefficient in gluon plasmas in a self-similar regime using real-time lattice techniques. We observe that the time-evolution of the momentum diffusion coefficient is consistent with a t^(-5/7) power law, as predicted by HTL perturbation theory and self-similarity. Using HTL with our recently acquired data on the spectral function of over-occupied...

Anisotropic flow is well understood as a hydrodynamic response to spatial anisotropies in the system density at early times. This response function can be written explicitly as a systematic expansion in terms of length scales, such that the leading contribution is the familiar eccentricity $\varepsilon_n$ that represents global structure. These relations have allowed for direct connections...

We investigate the importance of different features of the initial geometry to anisotropic flow fluctuations in heavy-ion collisions. To that end, we explore the hydrodynamic response of differential flow harmonics $v_n(p_T)$ to generalized eccentricities $\epsilon_{n,m}$ of the initial density profile within a realistic hydrodynamic model. Special attention is paid to two-particle angular...

One of the primary goals of flow studies in heavy-ion collisions during recent years is a better understanding of the transport properties of the quark-gluon plasma (QGP), such as the temperature dependence of the shear viscosity to entropy ratio, $\eta/s(T)$. Flow observables, such as the higher order harmonics (n>3) and their non-linear responses to the initial state anisotropy have a strong...

In proton-nucleus collisions, the top quark is a novel and theoretically precise probe of the nuclear gluon density at high virtualities $Q^2\approx m_{\mathrm{top}}$ and in the less explored high Bjorken-$x$ region. The first observation of the inclusive $\mathrm{t\bar{t}}$ production has been performed using 174$\pm$6 $\mathrm{nb}^{-1}$ of data in pPb collisions at $\sqrt{\smash...

The sPHENIX detector at RHIC, together with the accelerator's unique

capabilities, will enable a spectrum of new or improved measurements

enhancing our understanding of the initial state for nuclear

collisions. Specifically, sPHENIX measurements in spin polarized

proton-proton and proton-nucleus collisions will reveal more about how

partons behave in a nuclear environment, explore spin-spin...

In relativistic kinetic theory, the one-particle distribution function is approximated by an asymptotic perturbative power series in Knudsen number which is divergent. For the Bjorken flow, we expand the distribution function in terms of its moments and study their nonlinear evolution equations. The resulting coupled dynamical system can be solved for each moment consistently using a...

Ever since the discovery of the quark-gluon plasma (QGP) the location of the critical point in the QCD phase diagram - the end point of the supposed first-order transition between hadronic matter and the QGP - has been a principal research goal for heavy-ion collision experiments at RHIC. We use the gauge/gravity duality to study a four-dimensional, strongly-coupled gauge theory with a...

An ongoing question in the field is if the collectivity originating in small systems arises from:

- Flow scenario: initial conditions coupled to relativistic hydrodynamics leading to independent particle emissions from the fluid hyper-surface.

or

- Non-flow scenario: genuine 2,4 etc particle correlations from, e.g. a saturation framework.

We note that, in general, the experimentally...

Two particle correlations have been used extensively to study hydrodynamic flow patterns in heavy-ion collisions. In small collision systems, such as p+p and p+A, where particle multiplicities are much smaller than in A+A collisions, non-flow effects from jet correlations, momentum conservation, particle decays, etc. can be significant, even when imposing a large pseudorapidity gap between the...

Centrality fluctuations is one of the main uncertainties for interpreting the centrality dependence of many experimental observables. The centrality fluctuation is constrained by selection based on particle multiplicity in a reference subevent, and contributes to observables measured in another subevent. Due to the asymmetry between forward- and backward-going participating nucleons, the...

We present the first computation of the NLO photon+dijet impact factor in e+A DIS at small $x$. When combined with the recent derivation of JIMWLK small $x$ evolution to NLL$x$ accuracy, this result provides us with a prediction of the photon+dijet cross-section in e+A DIS to

O($\alpha_S^3 \ln(1/x)$) accuracy. The comparison of this result with photon+dijet measurements at a future EIC...

The proposed high-luminosity high-energy Electron Ion Collider (EIC) will provide one of the cleanest environments to precisely determine the nuclear parton distribution functions (nPDFs) in a wide x-$Q^{2}$ phase space. Heavy flavor production at the EIC can access up to the confinement boundary, which allows us to directly study nPDFs, quark/gluon fragmentation processes, and energy loss...

I discuss conformal properties of TMD operators and present the

result of the conformal rapidity evolution of TMD operators in the Sudakov region

The applicability of hydrodynamical models in the extreme conditions produced in heavy ion collisions has not yet been properly understood theoretically. This happens mostly because the derivation of hydrodynamics from microscopic theory often relies on the assumption that the system is sufficiently close to equilibrium -- something difficult to justify in the rapidly expanding systems created...

The next-to-leading order (NLO) Balitsky-Kovchegov (BK) equation describing the high-energy evolution of the scattering between a dilute projectile and a dense target suffers from instabilities unless it is supplemented by a proper resummation of the radiative corrections enhanced by large transverse logarithms. Earlier studies have shown that if one expresses the evolution in terms of the...

The factorization breaking of collective flow in transverse momentum or in pseudorapidity is equivalent to a small decorrelation of flow in different phasespace regions. ATLAS has measured, besides the usual factorization breaking (including both flow magnitude and angle decorrelation), the flow angle decorrelation in pseudorapidity. The latter accounts for about half of the total...

Measurements of dijet production and photo-nuclear interactions in heavy-ion collisions probe several nuclear mechanisms. In particular, dijet measurements in pPb collisions have been shown to be one of the most important tools for constraining the gluon nuclear parton distribution functions (PDFs) at large Bjorken-x. Dijet production in pp and pPb collisions at a nucleon-nucleon...

In this talk, first results on diffraction measurements in pPb collisions will be presented. This measurement utilizes the larger rapidity acceptance of the CMS detector using forward calorimeters such as the forward hadronic calorimeters HF, CASTOR and ZDC. This measurement provides important information for models related to the initial state in pPb collisions, and can also be used to tune...

The measurements of the flow phenomena in Xe+Xe and Pb+Pb collisions provide an excellent opportunity to study the interplay of viscous effects -- which diminish the azimuthal anisotropies more in Xe+Xe compared to Pb+Pb -- and initial geometry fluctuations which have an opposite effect. With the recently developed techniques, used for suppression of non-flow correlations in small systems,...

We study the longitudinal decorrelations of elliptic, triangular and quadrangular flows in heavy-ion collisions at the LHC and RHIC energies. The event-by-event CLVisc (3+1)-dimensional hydrodynamics model, combined with the fully fluctuating AMPT initial conditions, is utilized to simulate the space-time evolution of the strongly-coupled quark-gluon plasma. Detailed analysis is performed for...

Principal Component Analysis (PCA) is a mathematical tool that can capture the most important information in data. As one of the unsupervised algorithms of machine learning, PCA is good at discovering modes or hidden patterns in huge amount of data. It has seen successful applications of PCA in computer vision, data science and physics. Compared with deep learning algorithms, the advantage of...

We present a first-principles description of the primordial state of relativistic nucleus-nucleus collisions, whose density fluctuations and anisotropy we evaluate in the color glass condensate (CGC) framework of high-energy QCD. Relating the primordial anisotropy of the system in our approach to the measured final-state anisotropic flow through a simple linear mapping, we achieve an excellent...

The IP-Jazma model was constructed to elucidate which features of calculations in

the color glass condensate framework are attributable to simple geometry and scaling, and which are manifestations of more complex physics. In this talk we detail comparisons with CGC calculations in the dilute-dense limit, in the dense-dense limit (via IP-Glasma), and more phenomenological models such as...

Jets and photons have been studied to constrain the initial and final stages of collisions between two large nuclei at the Large Hadron Collider.

Measurements of photon and jet production $p$+Pb collisions are potentially sensitive to novel effects such as gluon saturation, the onset of non-linear QCD, and the energy loss of partons in the nuclear matter. In A+A collisions jets are modified...

ATLAS measurements of azimuthal anisotropy and suppression of muons from heavy flavor decays in Pb+Pb collisions are presented. The measurements are extended to smaller systems of $p$+Pb and $pp$ collisions, where no significant modification of the heavy flavor production are observed.In the smaller systems, a template fit method is used to subtract non-flow contributions using simultaneous...

We propose an approach to extract the spatial anisotropy of QGP formed in ultrarelativistic heavy-ion collisions from measured high-pt observables $R_{AA}$ and $v_2$. We show, through analytical arguments, numerical calculations, and comparison with experimental data, that $v_2/(1-R_{AA})$ reaches a well-defined saturation value at high $p_\perp$, which is in turn proportional to the initial...

This talk presents ATLAS measurements of azimuthal anisotropies in $pp$ and $p$+Pb collisions, performed via two-, four- and six-particle correlations, with modifications to ensure suppression of correlations arising from jets and dijets. In $pp$ collisions, the strength of the correlations quantified by the anisotropy parameter $v_2$ does not show any dependence on the charged-particle...

Measurements of anisotropic flow in heavy-ion collisions are an important tool to investigate the nature of the created collectively expanding medium called the Quark-Gluon Plasma (QGP). Recently, striking similarities have been observed in numerous measurements in high multiplicity proton-proton and proton-lead collisions, where no such medium was expected.

In this...

The ALICE Collaboration studied extensively heavy-flavour production at mid- and forward rapidities in small systems at the LHC. The data provide precise tests for pQCD calculations based on the factorization approach and set constraints to Cold Nuclear-Matter effects that can modify heavy-flavour production in p-Pb collisions with respect to pp collisions. At...

To what extent are fluid-dynamic or particle-like excitations at the origin of the flow phenomena observed in pp, pA and AA collisions? And how does the interplay between these two sources of collectivity change as a function of system size and energy density? Here, we address this question in a simple transport theory that interpolates between free-streaming and viscous fluid dynamics. We...

The second- and third-order azimuthal anisotropy Fourier harmonics are studied in pPb collisions at $\sqrt{s_{_\text{NN}}}=8.16~\mathrm{TeV}$ over a wide range of event multiplicities. Multiparticle correlations are used to isolate global properties stemming from the collision overlap geometry. The second-order, ``elliptic'' harmonic moment is obtained with high precision through four-, six-,...

Our understanding of QCD under extreme conditions has advanced

tremendously following the discovery of the Quark Gluon Plasma and its

detailed characterisation in heavy ion collisions at RHIC and the LHC.

The sPHENIX experiment at RHIC will provide precision measurements of

jet, upsilon and open heavy flavor probes, complementing analogous

measurements at the LHC. The physics program enabled...

In order to investigate the origin of collectivity in small systems, the PHENIX experiment has collected data of p+Au, d+Au and $^3$He+Au collisions at 200 GeV, giving a unique set of initial geometries. In this talk we present a complete set of elliptic and triangular flow measurements, which taken together provide unprecedented model discrimination between initial-state momentum correlation...

The STAR Collaboration plans to design, construct, and install a suite of new detectors in the forward rapidity region (2.5 < $\eta$ < 4) over the next two years, enabling a program of novel measurements in pp, pA, and AA collisions. This extension of STAR’s kinematic reach will allow detailed studies of cold QCD physics at both very high and very low partonic momentum fraction, i.e. when the...

Measurements of ``small,'' p+A or d+A, systems at the LHC and RHIC have suggested possible collective flow and, for high event activity collisions, jet modification that may scale with Bjorken x. They also provide input to related questions of the initial state of the proton prior to and throughout its collision with the opposing heavy ion nucleus. This talk presents preliminary measurements...

Among the main LHC experiments, LHCb is the only detector that can run both in collider and fixed-target mode. Internal gas targets of helium, neon and argon have been used so far to collect samples corresponding to integrated luminosities up to 0.1 pb-1. An upgraded target, allowing for a wider choice of target gas species and increasing the gas density by up to two orders of magnitude, is...

Initial state geometry has proved to be decisively important for quantitative descriptions of collective behavior in large collision systems, such as PbPb and AuAu. One of the most remarkable lessons from LHC has been the discovery of collective behavior in small collision systems, but here the notion of spatial structure is not as obvious as in nuclear collisions. In Monte Carlo event...

We present a quantitative assessment of the impact a future Electron-Ion Collider would

have in the determination of parton distribution functions in the proton and parton-to-hadron

fragmentation functions through semi-inclusive deep-inelastic electron-proton scattering data.

Specifically, we estimate the kinematic regions for which the forthcoming data are

expected to have the most...

The 2015 U.S. Nuclear Physics Long-Range Plan recommended the realization of an electron-ion collider (EIC) as the next large construction project in the United States. A U.S.-based EIC has also recently been endorsed by the U.S. National Academy of Sciences.

With the design of an EIC, advancements in theory and further development of phenomenological tools, we are now preparing for the next...

Hosted by the Center for Frontiers in Nuclear Science at Miss Mamie's Spoonbread Too, 366 W 110th St, New York, NY 10025 (10 minute walk from Columbia)

We investigate the importance of different features of the initial geometry to anisotropic flow fluctuations in heavy-ion collisions. To that end, we explore the hydrodynamic response of differential flow harmonics vn(pT) to generalized eccentricities ϵn,m of the initial density profile within a realistic hydrodynamic model. Special attention is paid to two-particle angular correlations,...

Hydro simulations are compared with recent experimental data by CMS, on a Principle Component Analysis. The trends for the scaled leading and sub-leading components for n=2,3 agree with data. In contrast, for n=0 there is a qualitative disagreement: the leading component increases with $p_T$ while it is constant in data. Using a toy model where the principal components can be computed...

I discuss conformal properties of TMD operators and present the result of the conformal rapidity evolution of TMD operators in the Sudakov region.

Recent measurements of the $\Upsilon(1S)$, $\Upsilon(2S), and $\Upsilon(3S)$ mesons in pp, pPb and PbPb collisions at 5.02 TeV are presented. The analysis was performed as a function of rapidity and transverse momentum. In addition, the dependence on the event activity and collision centrality is studied in pPb and PbPb collisions, respectively. New results of the upsilon production in pPb...

Heavy quarks, owing to their large masses, are predominantly created in the initial hard scatterings in heavy-ion collisions. Therefore, they can play a crucial role in probing the initial-time dynamics in these collisions. Hydrodynamic model calculations suggest that the rapidity-odd directed flow ($v_{1}(y)$) of particles produced at mid-rapidity can originate from a tilt in the reaction...