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The scientific program will be devoted to new developments in nuclear physics, with an emphasis on the latest data and theoretical results from the following subject areas:
Talks will be arranged in both plenary and parallel sessions and there will be a poster session on Tuesday.
Plenary talks are 25'+5'
Parallel talks are 15'+5'
All slides should be in 4:3 aspect ratio
Posters should be of typical size (e.g. A0 format, 841 x 1189 mm) but there will be room for larger sizes. They will need to be light enough to tape to a wall using masking tape.
Event ID: 39861
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 and strong coupling. In this formulation, the transport coefficients of far-from-equilibrium fluid dynamics depend not only on the microscopic properties of the system but also on the nonlinear properties of the underlying state of the fluid itself. In contrast to previous works, no additional assumptions about the symmetries of the flow are necessary. An example of this proposal is constructed using Israel-Stewart theory and, in this case, the novel resummed transport coefficients decrease with increasing Knudsen number according to formulas that can be readily investigated in current numerical simulations of the quark-gluon plasma, which can be especially relevant to small collision systems.
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 determined from the solutions to these kinetic equations. In the case of a static homogeneous background we show that the long time tails obtained from hydro-kinetic equations reproduce the one-loop results derived from statistical field theory. We use these results to establish bounds on transport coefficients. We generalize the stochastic equation to a scale invariant background flow undergoing Bjorken expansion. We compute the leading fractional power
To better understand the dynamics of initial stages in heavy-ion collisions, we perform classical-statistical simulations of SU(2) gauge theory in 2+1 dimensions. We find that highly occupied non-Abelian plasmas approach the same 2+1D self-similar state at late times of their far-from-equilibrium evolution, irrespective of details of their initial conditions, and we determine the scaling exponents. We extract the spectral function non-perturbatively and show that for larger momenta than the mass scale p >> m, one sees a pronounced peak in the frequency domain, while at low momenta p < m, quasi-particle assumptions become invalid. The hard-thermal loop (HTL) formalism is not applicable to 2+1D gauge theories at low momenta p <= m, and indeed, our results are inconsistent with its predictions. This challenges our detailed understanding of plasma instabilities at initial stages that is mostly based on HTL calculations of highly anisotropic gluonic matter.
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 constant, the scalar field and the particle mass respectively. Our analytical studies are corroborated by numerical simulations of the spatial and momentum structure of overoccupied scalar fields in (2+1)-dimensions. Universal scaling of infrared modes, vortex-antivortex superfluid dynamics and the off-equilibrium formation of a Bose-Einstein condensate are observed. Our results for the universal scaling exponents are in agreement with those extracted in the numerical simulations of the GP equation. As in these simulations, we observe coarsening phase kinetics in the Bose superfluid with strongly anomalous scaling exponents relative to that of vertex resummed kinetic theory. Our relativistic field theory framework further allows one to study more closely the coupling between superfluid and normal fluid modes, specifically the turbulent momentum and spatial structure of the coupling between a quasi-particle cascade to the infrared and an energy cascade to the ultraviolet. We outline possible applications of the formalism to the dynamics of vortex-antivortex formation and to the off-equilibrium dynamics of the strongly interacting matter formed in heavy-ion collisions.
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 collisions. In this talk I will present first results for the flow of baryon number in holographic collisions away from the infinite coupling limit, which also means we study the collisions at a larger shear viscosity over entropy density ratio than
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 collisional kernel is given by the leading order
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 collisions is a powerful test of the binary scaling of hard processes as well as a reference for hot-matter effects on other probes.
The measurement of electroweak-boson production in p--Pb and Pb--Pb collisions at the LHC provides constraints on the nPDFs of (anti)quarks in phase-space regions which are poorly constrained from previous experiments. At forward rapidity (
In this contribution, focus will be given to the most recent ALICE electroweak-boson measurements. Exploiting the data collected by ALICE in 2015 and 2018, centrality and rapidity-differential measurements of the Z-boson production yield in Pb--Pb collisions at
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.
In the 2015 heavy-ion data-taking period at the LHC, the ATLAS experiment obtained 0.49/nb of the Pb+Pb data and 25/pb of the proton-proton data at the centre of mass energy of 5.02 TeV. The fully analysed data presented in this talk addresses the nuclear modification of the parton distribution functions PDF at a new level of precision. Comparison between the lead-lead and proton-proton systems gives an opportunity to subject the Glauber model used by all heavy ion experiments to a stringent test performed over a wide range of collision centralities.
Nuclear parton distribution functions (nPDFs) of quarks and antiquarks affect the production electroweak bosons in proton-lead (pPb) collision. In this presentation the measurement of Z bosons in pPb collision at center of mass energies of 5.02 TeV and 8.16 TeV with CMS is presented. The rapidity dependence is particularly sensitive to nPDFs, but further information can be gained by studying the mass dependence of DY production, measured for the first time in pPb collisions at 8.16 TeV, down to 15 GeV. In addition, differential measurements in the dimuon pt or
Quarkonia, bound states of either a charm and anti-charm quark pair (e.g.
Recently, proton-proton (pp) and proton-lead (p--Pb) collisions with high charged-particle multiplicities have been found to exhibit phenomena similar to those attributed to the QGP formation. Measuring quarkonia in such collisions could contribute to a better understanding of the underlying physics processes leading to these observations and in any case provide a more detailed understanding of their production mechanism.
ALICE has measured quarkonium production in both pp collisions for collision energies
Heavy quarks (charm and beauty) are effective probes to test perturbative QCD-based calculations in pp collisions and to study cold nuclear matter (CNM) effects such as gluon saturation, shadowing,
With the ALICE detectors, open heavy flavours are measured via the full reconstruction of hadronic decays of non-strange D mesons,
In this contribution, the production cross sections of D mesons and open heavy-flavour decay electrons measured at mid-rapidity, and open heavy-flavour decay muons measured at forward rapidity in pp collisions at
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 relative contributions of different production mechanisms of ccbar and bbar pairs in p+p collisions. For bottom production, data from p+Au places limits on possible cold nuclear modifications. Measuring the in Drell-Yan cross-section in p+p and p+A collisions constrains nuclear parton distribution functions and furthers our understanding of initial state effects.
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 neutron distribution is larger than the proton one, resulting in a larger amount of neutrons distributed on the outer layers of the nucleus.
We implement the neutron skin together with nucleon-nucleon correlations, in the initial nuclear distribution of the SMASH transport model [2]. With this new state-of-the-art nuclear parametrization [3] we look at different collision systems (Pb+Pb, Zr+Zr, Ru+Ru) at RHIC energies i.e.
[1] Phys. Rev. Lett. 112, 242502
[2] Phys. Rev. C 94, 054905
[3] arXiv:1811.10078v1
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 perturbations in the transverse plane, based on the Boltzmann equation in relaxation time approximation. We discuss the approach towards viscous hydrodynamics along with the emergence of various scaling phenomena for conformal systems. By comparing our results obtained in the relaxation time approximation to previous calculations in QCD kinetic theory, we further address the question which macroscopic features of the energy momentum tensor are sensitive to the underlying microscopic dynamics.
The elliptic and triangular flow coefficients,
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 Baryon number, B, electric charge, Q, and strangeness, S, into the hydrodynamic description in order to have relevant theoretical predictions. This requires knowledge of an equation of state that contains thermodynamic information on the associated chemical potentials for B, Q, and S. In this work, we use the most up-to-date equation of state which includes all of the necessary thermodynamic information to make relevant predictions about the effect of transport coefficients on system dynamics. In particular, we will explore how a large bulk viscosity near the critical point could lead to effects such as the possibility of a cavitating system, as well as the slowing down of dynamics leading to a longer lifetime of the fluid.
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 ultra-relativistic heavy-ion collision experiments. In this talk, the question of how much we can learn about the early-time momentum anisotropies by studying the yield and flow of electromagnetic probes will be addressed. In particular, we compare the sensitivity of hadronic and electromagnetic probes to the initial momentum anisotropy used in hydrodynamic calculations.
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 gluodynamics, we find that the main contribution to the diffusion coefficient arises from the longitudinal Landau damping in the spectral function and study further features of the signal. Finding consistent results between lattice simulations and HTL results is an important step forward in understanding the evolution of the diffusion coefficient at initial stages.
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
However, the initial conditions for hydrodynamics consist of an entire tensor
I will present a framework for including the effects of the full hydrodynamic initial conditions, along with numerical tests from full hydrodynamic simulations to demonstrate its efficacy. In addition, I will present an extension to include rapidity dependence.
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
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,
In this talk, we present the measurements of the symmetry-plane correlations and the non-linear coefficients up to the eighth harmonic order in Pb-Pb collisions at
In proton-nucleus collisions, the top quark is a novel and theoretically precise probe of the nuclear gluon density at high virtualities
The Large Hadron-electron Collider (LHeC) is a proposed upgrade of the
LHC at CERN. An ERL will provide electrons to collide with the HL-LHC,
HE-LHC and the FCC-hh proton beams to achieve centre-of-mass energies
1.3-3.5 TeV and luminosities
enlarge the kinematic plane by more than one order of magnitude
towards smaller
such configurations offer unprecedented possibilities to enlarge our
knowledge on parton densities through a complete unfolding of all
flavours, both in a single experimental setup and combined with data
from hadron colliders where precise factorisation tests can be
performed. In this talk we review the most recent developments on the
determination of proton PDFs and the measurement of
the LHeC and the FCC-eh.
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 and
spin-momentum correlations in the nucleon, and provide data to
investigate effects of non-universality. A potential upgrade to
sPHENIX with forward instrumentation could significantly enhance these
physics capabilities. The cold QCD nuclear physics program for the
proposed sPHENIX midrapidity detector as well as the enhanced program
enabled with forward upgrades will be presented.
Computing observables in high-energy collisions requires a functional average over the configurations of small-x gluons in the wave functions of the colliding hadrons. We discuss a method for performing biased averages, for example due to a multiplicity or centrality bias, where the gluon distributions of the hadrons are modified from their unbiased average. We consider specifically potential effects due to a bias on the correlator of two Wilson lines, i.e. the dipole scattering amplitude, and on azimuthal angular correlations of gluons at high transverse momentum (the "glasma graphs").
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 multi-parameter transseries which makes the constitutive relations inherit the same structure. A new non-perturbative dynamical renormalization scheme is born out of this formalism that goes beyond the linear response theory. As a result, the transport coefficients get dynamically renormalized at every order in the time-dependent perturbative expansion by receiving non-perturbative corrections present in the transseries. The renormalized transport coefficients feature a transition to their equilibrium fixed point, which is a neat diagnostics of transient non-Newtonian behavior. Furthermore, we show that the first dissipative correction to the distribution function is not only determined by the known effective shear viscous term but also a new high energy non-hydrodynamic mode. Finally, we briefly discuss some possible phenomenological applications of the proposed non-hydrodynamic transport theory.
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 first-order, second-order and crossover thermal phase transition. In the dual gauge theory we calculate the formation, evolution and saturation of the spinodal instability. We uncover a new surprising example of the applicability of hydrodynamics to systems with large gradients (JHEP 1706 (2017) 129 + upcoming work).
We discover with out-of-equilibrium shockwave collisions that in theories near a critical point a long-lived, quasi-static state may be formed. moreover, we show the Mueller-Israel-Stewart-type formulation of hydrodynamics to fail to describe pressures (Phys.Rev.Lett. 121 (2018), no.26, 261601) near a critical point. We provide the necessary correction terms and demonstrate that large second-order spatial derivatives need to be accounted for.
Recently collected data by the ATLAS experiment at the LHC offer opportunities to explore dynamic properties of quark-gluon plasma. A new tool to study these properties is the modified Pearson's correlation coefficient,
An ongoing question in the field is if the collectivity originating in small systems arises from:
or
We note that, in general, the experimentally measured
Using the Color-Glass Condensate (CGC) formalism in the (semi)dilute-(semi)dilute regime for
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 particles. A number of techniques to subtract the non-flow contribution have been developed by experiments at the LHC for use in p+p and p+Pb collisions. Recently, experiments at RHIC have explored the possibility of adopting these techniques for small collision systems at lower energies. In this talk, we systematically test these techniques using the Monte Carlo generators PYTHIA and HIJING, which do not include any collective flow, and AMPT, which does. We find that it is crucial to examine the results of such tests at the LHC and RHIC both as a function of multiplicity and particle
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 number of sources for particle production is a function of
We present the first computation of the NLO photon+dijet impact factor in e+A DIS at small
O(
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-
I discuss conformal properties of TMD operators and present the
result of the conformal rapidity evolution of TMD operators in the Sudakov region
The observed azimuthal modulations of long-range correlations in pseudorapidity in small systems like pp or p-Pb collisions show strikingly similar features to those seen in heavy ion collisions. Many theoretical approaches to interpreting this effect have been developed. However, it is still unclear whether these long-range correlations are due to final or initial state effects.
To further investigate these effects, we studied long-range correlations as a function of transverse momentum in very high multiplicity pp collisions at
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 rapidity of the dilute projectile, the dominant, anti-collinear, contributions can be resummed to all orders. However, in applications to physics, the results must be re-expressed in terms of the rapidity of the dense target (which corresponds to Bjorken x). We show that although they lead to stable evolution equations, resummations expressed in the rapidity of the projectile show a strong, unwanted, scheme dependence when translated in the rapidity of the target. We circumvent this problem by working directly with the rapidity of the dense target [1]. This avoids the large anti-collinear contributions but introduces new, collinear, instabilities, which are however milder since disfavoured by the typical BK evolution. We propose several prescriptions for resumming these new double logarithms and find only little scheme dependence. The resummed equations are non-local in rapidity and can be extended to full NLO accuracy. We present the first applications of these resummed equations to deep inelastic scattering at HERA.
[1] B. Ducloué et al, e-Print: arXiv:1902.06637 [hep-ph]
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 centre-of-mass energy of 5.02 TeV is reported with the data samples collected with the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet pseudorapidity distributions are measured as a function of dijet average transverse momentum in order to study the nuclear modifications of PDFs at various factorization scales. The final results from pp and pPb data samples are compared with next-to-leading-order perturbative QCD predictions obtained from both nucleon and nuclear PDFs. A significant modification of dijet pseudorapidity distributions in pPb collisions with respect to the measured pp reference is observed which indicates that the gluon PDF in lead ions is modified and the results are incompatible with predictions with DSSZ PDF without gluon EMC effects. Photo-nuclear jets are also measured in pp and pPb collision systems. The yield and angular correlation of low-pT jets at forward rapidity,
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 Monte Carlo event generators of cosmic ray physics. In addition, recent results on exclusive vector meson photoproduction of Rho0, J/psi and Upsilon in both pPb and PbPb collisions will be presented. The measured integrated and differential cross sections as a function of rapidity and transverse momentum will be compared to theoretical models.
In quantum mechanics, Einstein, Podolsky, and Rosen (EPR) formulated an apparent paradox of quantum theory in 1935. They considered two quantum mechanical systems were first brought to interaction, then later separated to large distance. A measurement of a physical observable in one system would have an immediate effect on the conjugate observable in the other system, even when they are causally disconnected. Therefore, EPR concluded that there is an inconsistency in the quantum theory. In the parton model formulated by Bjorken, Feynman, and Gribov, the partons inside of a nucleon are viewed as ``quasi-free" particles when they are boosted into the infinite momentum frame, where the parton probed by the virtual photon is causally disconnected from the rest of the nucleon. Since the parton and the rest of the nucleon have to form a color-singlet state due to confinement, we encounter the EPR paradox at sub-nucleonic states for the first time. In this work we propose a resolution of this apparent paradox via quantum entanglement. We test this idea by measuring the entanglement entropy of the system using data from proton-proton collisions at the Large Hadron Collider, and our results provide a strong direct indication of quantum entanglement at sub-nucleonic scales.
Intense electromagnetic fields are created in the quark-gluon plasma by the external ultra-relativistic valence charges. The time-evolution and the strength of this field are strongly affected by the electrical conductivity of the plasma. Yet, it has recently been observed that the effect of the magnetic field on the plasma flow is small. We compute the effect of plasma flow on magnetic field and demonstrate that it is less than 10\%. These observations indicate that the plasma hydrodynamics and the dynamics of electromagnetic field decouple. Thus, it is a very good approximation, on the one hand, to study QGP in the background electromagnetic field generated by external sources and, on the other hand, to investigate the dynamics of magnetic field in the background plasma. We also argue that the wake induced by the magnetic field in plasma is negligible.
We study relaxation dynamics of chiral transport phenomena and spin polarization in Quark-Gluon Plasma in both weakly and strongly coupled regimes. These relaxation dynamics determine the important dynamical time scale for achieving equilibrium spin-polarization of quasi-particles in the presence of magnetic field and fluid vorticity, which are time-dependent in heavy-ion collisions. This is also important in the time-dependence of the Chiral Vortical Effect. Our results should be crucial in a reliable quantitative study of
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 in heavy ion collisions. In this talk we propose a more general derivation of relativistic hydrodynamics from kinetic theory, in which the fluid is assumed to be close to an isotropic nonequilibrium state instead of an equilibrium one. We demonstrate that, for a wide variety of nonequilibrium states, a hydrodynamic theory that is identical to the traditional hydrodynamic equations applied to heavy ion collisions is obtained. The only difference appears in the form of the transport coefficients that enter the equations of motion. Simulations of the Boltzmann equation equation in 0+1D Bjorken flow in the ultrarelativistic limit are performed to demonstrate this effect, showing that the same evolution for the energy-momentum tensor is obtained even when the momentum distribution function of partons is very different from an equilibrium one.
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 decorrelation. These observations are confirmed in hydrodynamic calculations for the flow decorrelation, both in pseudorapidity [1] and in transverse momentum [2]. The general relation between flow angle and flow magnitude decorrelation can be understood within a simple model with a random component of the flow vector [3].
Our work makes also predictions for additional observables, that could be tested experimentally.
[1] P. Bozek, W. Broniowski, Phys. Rev. C 97 (2018) 034913.
[2] P. Bozek, Phys. Rev. C98 (2018) 064906.
[3] P. Bozek, H. Mehrabpour, in preparation
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, applied to 0.49 nb
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 the longitudinal decorrelations of flow vectors, flow magnitudes and flow orientations. We find strong correlations between final-state longitudinal decorrelations of anisotropic flows and initial-state longitudinal structures and collision geometry: the decorrelation of elliptic flow shows a non-monotonic centrality dependence due to initial elliptic geometry, while the longitudinal flow decorrelations are typically larger in lower energy and less central collisions where the mean lengths of the string structure are shorter in the initial states.
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 PCA lies in its simple and elegant mathematical formulation, which is understandable and traceable. In this talk, we implement PCA to analyze collective flow in Relativistic Heavy-Ion Collisions.
In the first part [1], we demonstrate the ability of PCA to automatically discover flow without any guidance from human beings. PCA is applied to particle yields distribution as a function of transverse plane angle
In the second part [2], as another application of PCA, we study factorization breaking in two-particle correlation
[1] Z. Liu, W. Zhao and H. Song, in preparation.
[2] Z. Liu, A. Behera, H. Song and J. Jia, in preparation.
[3] CMS Collaboration, Phys.Rev. C.96.064902
[4] A. Mazeliauskas and D. Teaney, Phys.Rev. C91 (2015) no.4, 044902
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 description of both RHIC and LHC data.
Our description does not make any explicit reference to the usual, ad hoc fluctuations due to the random positions of the incoming nucleons: Primordial initial-state fluctuations are generated solely by McLerran-Venugopalan correlators of color charges. The good agreement found with the data implies, then, that QCD interactions alone can provide the system with enough density fluctuations to explain the measured triangular flow, and elliptic flow fluctuations.
This suggests a fundamental paradigm shift in our understanding of fluctuations in heavy-ion collisions: At ultrarelativistic energies, the standard Monte Carlo Glauber picture of nuclear collisions, which until now has been understood as the dominant source of fluctuations, can be abandoned.
Based on:
https://arxiv.org/abs/1902.07168
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 Trento. Our result indicate that many results attributed in the literature to complex QCD phenomena are in fact dominated by simple geometric effects.
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
This talk presents ATLAS measurements of azimuthal anisotropies in
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 talk, we will present the latest ALICE measurements of flow coefficients, and their magnitude correlations using Symmetric Cumulants for charged particles in 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 discuss how this transport theory accounts for the centrality dependence of
based on A. Kurkela, U.A. Wiedemann and B. Wu, arXiv:1803.02072 arXiv:1805.04081 and work in preparation.
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
The recent finding of collective behavior of particles emitted in small system collisions calls for reexamination of such systems to determine whether or effects beyond the initial state nuclear effects play a significant role.
High
PHENIX has measured mid to high
We propose an approach to extract the spatial anisotropy of QGP formed in ultrarelativistic heavy-ion collisions from measured high-pt observables
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 mid-rapidity the study of the angular correlation of heavy-flavour particles with charged particles produced in the event allows us to further characterize charm and beauty production and fragmentation processes in pp collisions and investigate their possible modifications due to nuclear effects in p-Pb and Pb-Pb collisions. In p-Pb collisions these studies can also set constraints on the dependence of Cold Nuclear-Matter effects on the collision geometry and on the density of final-state particles. In addition, the study of the angular correlation pattern in p-Pb collisions as a function of the event multiplicity allows studying the features of long-range correlations similar to the one found in heavy-ion collisions whose origin is still debated. Finally, the measurement of heavy-flavour jets, besides constituting the necessary baseline for similar studies in the Pb-Pb collision system, gives more direct access to the initial parton kinematics and can provide further constraints on pQCD based models.
In this contribution, the latest ALICE results from pp and p-Pb collisions collected during the LHC Run 2 will be presented. In particular, measurements of the angular correlation of D mesons and heavy-flavour decay electrons with charged particles in pp and p-Pb collisions will be shown. The measurement of heavy-flavour decay leptons elliptic flow in p-Pb collisions at high multiplicity at mid-and forward rapidities will also be presented together with the
I will present the first calculation of all
The second- and third-order azimuthal anisotropy Fourier harmonics are studied in pPb collisions at elliptic'' harmonic moment is obtained with high precision through four-, six-, and eight-particle correlations and, for the first time, the third-order,triangular'' harmonic moment is studied using four-particle correlations. A sample of peripheral PbPb collisions at
In order to investigate the origin of collectivity in small systems, the PHENIX experiment has collected data of p+Au, d+Au and
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 of correlations between mid-rapidity charged tracks and high-rapidity event activity measured by scintillator tiles in
Simulations of relativistic heavy-ion collisions based on viscous hydrodynamics provide an accurate description of the bulk observables measured at RHIC and LHC beam energies, including identified particle yields, mean
It was thus surprising when the multiparticle correlations measured in high-multiplicity proton-lead collisions were found to be similar in magnitude to those observed in lead-lead collisions. The observation suggests that hydrodynamic behavior could be manifest in small droplets of quark-gluon plasma (QGP), and that flow might develop at length scales smaller than a proton.
In this work, we assume the existence of hydrodynamic flow in small collision systems and evaluate the likelihood of our assertion using Bayesian inference. Specifically, we model the dynamics of proton-lead and lead-lead collisions at 5.02 TeV using QGP initial conditions with parametric nucleon substructure, a pre-equilibrium free-streaming stage, event-by-event viscous hydrodynamics with shear and bulk coupling, and a microscopic hadronic afterburner to simulate the dynamics of the collision below the QGP transition temperature.
The model is evaluated on a scaffolding of parameter points, and emulators are trained to interpolate the model predictions at intermediate regions of parameter space. Markov chain Monte Carlo importance sampling is then used to explore the Bayesian posterior probability distribution as a function of the model input parameters.
We use the resulting posterior distribution to sample preferred regions of parameter space and evaluate the performance of the model with optimally chosen parameter values This semi-exhaustive model validation enables us to to comment on the implied viability of hydrodynamics in small collision systems subject to the approximations of the chosen framework. We also present marginalized posterior distributions for each model input parameter, e.g. nucleon substructure degrees of freedom, which demonstrate the constraining power of global statistical analysis and reveal new insight into nuclear matter at extreme temperatures and densities.
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 generators, ad hoc phenomenological schemes are usually employed with clear room for improvement. In this talk we present progress on including a transverse space structure of pp collisions based on the Mueller dipole formulation of QCD, into the Pythia8 event generator. This formalism has the advantage that parameters can be estimated from inclusive quantities in ep and pp collisions, such that the spatial structure becomes a true prediction of the model. Besides the importance for collective behavior, in particular in pp, but also in fluctuation dominated pA and peripheral AA collisions, the dipole picture also serves as an important starting point for including electron-ion initial states in the model for heavy-ion collisions in Pythia8, the Angantyr framework, a perspective which also will be discussed.
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 by these
measurements will advance understanding of QCD dynamics through all
phases of the collision, connecting the initial stage in which one
expects large temperature and parton density differences between
collisions at RHIC and LHC energies, to subsequent stages in which the
properties of scale sensitive probes can be further modified. We will
describe the current status of the sPHENIX detector and its physics
program, with an emphasis on the physics program enabled by the
experiment's large coverage, high rate capability and precision
vertexing.
The TMD parton distributions can have azimuthal asymmetry in the transverse plane for the transversely polarized nucleon. This is called the Sivers effect and is phenomenologically important for the description of single spin asymmetries. I will present our recent calculation of the gluon Sivers function at small-x obtained by using the known connection between the Sivers function and the odderon.
The STAR Collaboration plans to design, construct, and install a suite of new detectors in the forward rapidity region (2.5 <
[1] “The STAR Forward Calorimeter System and Forward Tracking System,” https://drupal.star.bnl.gov/STAR/starnotes/public/sn0648
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 going to be installed for the LHC Run 3. This offers a unique opportunity for measurements of great interest going from QCD to astroparticle in unexplored kinematic regions. Results and prospects on open and hidden charm productions will be presented, which can provide crucial constraints on cold nuclear matter effects and nPDF at large x.
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 significant impact in the precision of these distributions,
computing the respective correlation and sensitivity coefficients. Using a reweighting
technique for the sets of simulated data with their realistic uncertainties for two different
center-of-mass energies, we analyse the resulting new sets of parton distribution functions and
fragmentation functions, which have significantly reduced uncertainties.
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 step in subnuclear tomographic imaging. The collider's large range of center-of-mass energy, in combination with very high luminosity and polarization of both the lepton and the hadron beams, will open a unique opportunity for very high precision measurements of both cross sections and spin-asymmetries. This will allow us for a detailed investigation of the partonic substructure of hadrons in multi-dimensions, as well as addressing the role of orbital angular momentum with respect to the nucleon spin.
Generalized parton distributions (GPDs) describe the multi-dimensional partonic structure of a nucleon in coordinate space, providing new information about the internal dynamics of quarks and gluons. Extraction of GPDs from hard exclusive processes and all related probes, is a pillar of the EIC science program.
This talk will highlight key measurements, experimental challenges, and finally discuss the EIC's expected impact over the current knowledge of the partonic multidimensional structure of hadrons in space coordinates.
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)
Recently collected data by the ATLAS experiment at the LHC offer opportunities to explore dynamic properties of quark-gluon plasma. A new tool to study these properties is the modified Pearson's correlation coefficient,
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, characterized in detail by the principal-component analysis (PCA). We address the relevance of non-linear response, as well as the stability of the results against the inclusion of extra eccentricities. Additionally, we study new effects from multiplicity fluctuations, which could lead to redundancies in the experimental PCA data.